The auditory analyzer perceives air vibrations and transforms the mechanical energy of these vibrations into impulses, which are perceived in the cerebral cortex as sound sensations.

The perceptive part of the auditory analyzer includes the outer, middle and inner ear (Fig. 11.8.). The outer ear is represented by the auricle (sound catcher) and the outer ear canal, the length of which is 21-27 mm and the diameter is 6-8 mm. The outer and middle ears are separated by the eardrum - a membrane that is poorly pliable and weakly stretchable.

The middle ear consists of a chain of interconnected bones: the malleus, the incus and the stapes. The handle of the malleus is attached to the tympanic membrane, the base of the stapes is attached to the oval window. This is a kind of amplifier that amplifies vibrations 20 times. The middle ear also has two small muscles that attach to the bones. Contraction of these muscles leads to a decrease in vibrations. The pressure in the middle ear is equalized by the Eustachian tube, which opens into the oral cavity.

The inner ear is connected to the middle ear by the oval window, to which the stapes is attached. In the inner ear there is a receptor apparatus of two analyzers - perceptive and auditory (Fig. 11.9.). The hearing receptor apparatus is represented by the cochlea. The cochlea, 35 mm long and having 2.5 whorls, consists of a bony and membranous part. The bone part is divided by two membranes: the main and vestibular (Reisner) into three canals (upper - vestibular, lower - tympanic, middle - tympanic). The middle part is called the cochlear passage (membranous). At the apex, the upper and lower canals are connected by a helicotrema. The upper and lower canals of the cochlea are filled with perilymph, the middle ones with endolymph. Perilymph resembles plasma in ionic composition, endolymph resembles intracellular fluid (100 times more K ions and 10 times more Na ions).

The main membrane consists of weakly stretched elastic fibers, so it can vibrate. On the main membrane - in the middle channel - there are sound-perceiving receptors - the organ of Corti (4 rows of hair cells - 1 internal (3.5 thousand cells) and 3 external - 25-30 thousand cells). Above is the tectoreal membrane.

Mechanisms sound vibrations . Sound waves passing through the external auditory canal vibrate the eardrum, which causes the bones and membrane of the oval window to move. The perilymph oscillates and the oscillations fade towards the apex. Vibrations of the perilymph are transmitted to the vestibular membrane, and the latter begins to vibrate the endolymph and the main membrane.

The following is recorded in the cochlea: 1) Total potential (between the organ of Corti and the middle canal - 150 mV). It is not associated with the conduction of sound vibrations. It is due to the level of redox processes. 2) Action potential of the auditory nerve. In physiology, a third - microphone - effect is also known, which consists of the following: if electrodes are inserted into the cochlea and connected to a microphone, having previously amplified it, and various words are pronounced in the cat’s ear, the microphone reproduces the same words. The microphonic effect is generated by the surface of the hair cells, since deformation of the hairs leads to the appearance of a potential difference. However, this effect exceeds the energy of the sound vibrations that caused it. Hence the microphone potential is a complex transformation of mechanical energy into electrical energy, and is associated with metabolic processes in hair cells. The location of the microphonic potential is the region of the hair roots of the hair cells. Sound vibrations acting on the inner ear impose a microphonic effect on the endocochlear potential.

The total potential differs from the microphone potential in that it reflects not the shape of the sound wave, but its envelope and occurs when high-frequency sounds act on the ear (Fig. 11.10.).

The action potential of the auditory nerve is generated as a result of electrical excitation occurring in the hair cells in the form of a microphone effect and a sum potential.

There are synapses between hair cells and nerve endings, and both chemical and electrical transmission mechanisms take place.

Mechanism for transmitting sound of different frequencies. For a long time, the resonator system dominated in physiology. Helmholtz theory: Strings of different lengths are stretched on the main membrane; like a harp, they have different vibration frequencies. When exposed to sound, that part of the membrane that is tuned to resonance at a given frequency begins to vibrate. Vibrations of the tensioned threads irritate the corresponding receptors. However, this theory is criticized because the strings are not tensioned and their vibrations include too many membrane fibers at any given moment.

Deserves attention Bekes theory. There is a resonance phenomenon in the cochlea, however, the resonating substrate is not the fibers of the main membrane, but a column of liquid of a certain length. According to Bekeshe, the higher the frequency of sound, the shorter the length of the oscillating column of liquid. Under the influence of low-frequency sounds, the length of the oscillating column of liquid increases, capturing most of the main membrane, and not individual fibers vibrate, but a significant part of them. Each pitch corresponds to a certain number of receptors.

Currently, the most common theory of perception of sound of different frequencies is “theory of place”, according to which the participation of perceiving cells in the analysis of auditory signals is not excluded. It is assumed that hair cells located in different parts of the main membrane have different lability, which affects sound perception, i.e. we are talking about tuning hair cells to sounds of different frequencies.

Damage in various parts of the main membrane leads to a weakening of electrical phenomena that occur when irritated by sounds of different frequencies.

According to the resonance theory, different parts of the main plate respond by vibrating their fibers to sounds of different pitches. The strength of sound depends on the magnitude of the vibrations of the sound waves that are perceived eardrum. The stronger the sound, the greater the vibration of the sound waves and, accordingly, the eardrum. The pitch of the sound depends on the frequency of vibration of the sound waves. The frequency of vibrations per unit time will be greater. perceived by the organ of hearing in the form of higher tones (fine, high-pitched sounds of the voice) Lower frequency vibrations of sound waves are perceived by the organ of hearing in the form of low tones (bass, rough sounds and voices).

Perception of pitch, sound intensity, and sound source location begins when sound waves enter the outer ear, where they vibrate the eardrum. Vibrations of the tympanic membrane through the system of auditory ossicles of the middle ear are transmitted to the membrane of the oval window, which causes vibrations of the perilymph of the vestibular (upper) scala. These vibrations are transmitted through the helicotrema to the perilymph of the scala tympani (lower) and reach the round window, displacing its membrane towards the cavity of the middle ear. Vibrations of the perilymph are also transmitted to the endolymph of the membranous (middle) canal, which causes the main membrane, consisting of individual fibers stretched like piano strings, to vibrate. When exposed to sound, the membrane fibers begin to vibrate along with the receptor cells of the organ of Corti located on them. In this case, the hairs of the receptor cells come into contact with the tectorial membrane, and the cilia of the hair cells are deformed. First, a receptor potential appears, and then an action potential (nerve impulse), which is then carried along auditory nerve and is transmitted to other parts of the auditory analyzer.

Hearing organ consists of three sections - outer, middle and inner ear. The outer and middle ears are auxiliary sensory structures that conduct sound to the auditory receptors in the cochlea (inner ear). The inner ear contains two types of receptors - auditory (in the cochlea) and vestibular (in the structures of the vestibular apparatus).

The sensation of sound occurs when compression waves caused by vibrations of air molecules in the longitudinal direction strike the auditory organs. Waves from alternating sections
compression (high density) and rarefaction (low density) of air molecules spread from a sound source (for example, a tuning fork or string) like ripples on the surface of water. Sound is characterized by two main parameters - strength and height.

The pitch of a sound is determined by its frequency, or the number of waves in one second. Frequency is measured in Hertz (Hz). 1 Hz corresponds to one complete oscillation per second. The higher the frequency of a sound, the higher the sound. The human ear distinguishes sounds ranging from 20 to 20,000 Hz. The greatest sensitivity of the ear occurs in the range of 1000 - 4000 Hz.

The strength of sound is proportional to the amplitude of the sound wave and is measured in logarithmic units - decibels. One decibel is equal to 10 lg I/ls, where ls is the threshold sound intensity. The standard threshold force is taken to be 0.0002 dyn/cm2 - a value very close to the limit of human audibility.

Outer and middle ear

The auricle serves as a speaker, directing sound into the auditory canal. In order to get to the eardrum that separates the outer ear from the middle ear, sound waves must pass through this channel. The vibrations of the eardrum are transmitted through the air-filled cavity of the middle ear along a chain of three small auditory ossicles: the malleus, the incus and the stapes. The malleus connects to the eardrum, and the stapes connects to the membrane of the oval window of the cochlea of ​​the inner ear. Thus, vibrations of the tympanic membrane are transmitted through the middle ear to the oval window through a chain of malleus, incus and stapes.

The middle ear plays the role of a matching device, ensuring the transmission of sound from a low-density environment (air) to a more dense one (fluid of the inner ear). The energy required to impart oscillatory movements to any membrane depends on the density of the medium surrounding this membrane. Vibrations in the fluid of the inner ear require 130 times more energy than in air.

When sound waves are transmitted from the eardrum to the oval window along the chain of auditory ossicles, the sound pressure increases 30 times. This is due, first of all, to the large difference in the area of ​​the tympanic membrane (0.55 cm2) and the oval window (0.032 cm2). Sound from the large tympanic membrane is transmitted through the auditory ossicles to the small oval window. As a result, the sound pressure per unit area of ​​the oval window compared to the eardrum increases.

The vibrations of the auditory ossicles are reduced (damped) by the contraction of two muscles of the middle ear: the tensor tympani muscle and the stapes muscle. These muscles attach to the malleus and stapes, respectively. Their reduction leads to increased rigidity in the chain of auditory ossicles and a decrease in the ability of these ossicles to conduct sound vibrations in the cochlea. A loud sound causes a reflex contraction of the muscles of the middle ear. Thanks to this reflex auditory receptors snails are protected from the damaging effects of loud sounds.

Inner ear

The cochlea is formed by three spiral canals filled with fluid - the scala vestibularis (vestibular scale), the scala mediali and the scala tympani. The scala vestibular and scala tympani are connected at the distal end of the cochlea through the helicotrema opening, and the scala middle is located between them. The middle scala is separated from the scala vestibular by a thin Reisner membrane, and from the scala tympani by the main (basilar) membrane.

The cochlea is filled with two types of fluid: the scala tympani and scala vestibular contain perilymph, and the scala media contains endolymph. The composition of these fluids is different: the perilymph has a lot of sodium, but little potassium, the endolymph has little sodium, but a lot of potassium. Because of these differences in ionic composition, an endocochlear potential of about +80 mV occurs between the endolymph of the scala media and the perilymph of the scala tympani and vestibular. Since the resting potential of hair cells is approximately -80 mV, a potential difference of 160 mV is created between the endolymph and the receptor cells, which is important for maintaining hair cell excitability.

At the proximal end of the scala vestibuli there is an oval window. With low-frequency vibrations of the membrane of the oval window, pressure waves arise in the perilymph of the scala vestibularis. Fluid vibrations generated by these waves are transmitted along the scala vestibularis and then through the helicotrema to the scala tympani, at the proximal end of which there is a round window. As a result of the propagation of pressure waves into the scala tympani, vibrations of the perilymph are transmitted to the round window. When the round window, which plays the role of a damping device, moves, the energy of the pressure waves is absorbed.

Organ of Corti

The auditory receptors are hair cells. These cells are associated with the main membrane; in the human cochlea there are about 20 thousand of them. The endings of the cochlear nerve form synapses with the basal surface of each hair cell, forming the vestibulocochlear nerve (VIII point). The auditory nerve is formed by fibers of the cochlear nerve. The hair cells, the endings of the cochlear nerve, the integumentary and basilar membranes form the organ of Corti.

Excitation of receptors

As sound waves propagate in the cochlea, the covering membrane shifts, and its vibrations lead to excitation of the hair cells. This is accompanied by a change in ionic permeability and depolarization. The resulting receptor potential excites the endings of the cochlear nerve.

Pitch discrimination

The vibrations of the main membrane depend on the pitch (frequency) of the sound. The elasticity of this membrane gradually increases with distance from the oval window. At the proximal end of the cochlea (in the area of ​​the oval window), the main membrane is narrower (0.04 mm) and stiffer, and closer to the helicotrema it is wider and more elastic. Therefore, the oscillatory properties of the main membrane gradually change along the length of the cochlea: the proximal sections are more susceptible to high-frequency sounds, and the distal sections respond only to low sounds.

According to the spatial theory of pitch discrimination, the main membrane acts as a sound frequency analyzer. The pitch of the sound determines which part of the main membrane will respond to this sound with vibrations of the greatest amplitude. The lower the sound, the greater the distance from the oval window to the area with the maximum amplitude of vibrations. As a result, the frequency to which any hair cell is most sensitive is determined by its location; cells that respond predominantly to high tones are localized on a narrow, tightly stretched basilar membrane near the oval window; the receptors that perceive low sounds are located on wider and less tightly stretched distal sections of the main membrane.

Information about the height of low sounds is also encoded by the parameters of discharges in the fibers of the cochlear nerve; According to the “volley theory”, the frequency of nerve impulses corresponds to the frequency of sound vibrations. The frequency of action potentials in cochlear nerve fibers that respond to sounds below 2000 Hz is close to the frequency of these sounds; because in a fiber excited by a tone of 200 Hz, 200 impulses occur in 1 s.

Central auditory pathways

The fibers of the cochlear nerve go as part of the vestibulo-cochlear nerve to the medulla oblongata and end in its cochlear nucleus. From this nucleus, impulses are transmitted to the auditory cortex through a chain of interneurons of the auditory system located in the medulla oblongata (cochlear nuclei and superior olivary nuclei), in the midbrain (inferior colliculus) and thalamus (medial geniculate body). The "final destination" of the auditory canals is the dorsolateral edge of the temporal lobe, where the primary auditory area is located. This band-like area is surrounded by the associative auditory zone.

The auditory cortex is responsible for recognizing complex sounds. Here their frequency and strength are correlated. In the associative auditory area, the meaning of heard sounds is interpreted. Neurons of the underlying sections - the middle part of the olive, the inferior colliculus and the medial geniculate body - also carry out the attraction and processing of information about the sound and localization of sound.

Vestibular system

The labyrinth of the inner ear, containing auditory and balance receptors, is located within the temporal bone and is formed by planes. The degree of displacement of the cupula and, therefore, the frequency of impulses in the vestibular nerve innervating the hair cells depends on the magnitude of the acceleration.

Central vestibular pathways

The hair cells of the vestibular apparatus are innervated by fibers of the vestibular nerve. These fibers go as part of the vestibulocochlear nerve to the medulla oblongata, where they end in the vestibular nuclei. The processes of the neurons of these nuclei go to the cerebellum, reticular formation and spinal cord- motor centers that control body position during movements thanks to information from the vestibular apparatus, proprioceptors of the neck and organs of vision.

Receipt of vestibular signals to visual centers is of paramount importance for the important oculomotor reflex - nystagmus. Thanks to nystagmus, the gaze is fixed on a stationary object when moving the head. As the head rotates, the eyes slowly turn in the opposite direction, and therefore the gaze is fixed at a certain point. If the angle of rotation of the head is greater than that to which the eyes can turn, then they quickly move in the direction of rotation and the gaze is fixed on a new point. This rapid movement is nystagmus. When turning the head, the eyes alternately make slow movements in the direction of the turn and fast ones in the opposite mood.

The function of the hearing organ is based on two fundamentally different processes - mechanoacoustic, defined as a mechanism sound conduction, and neuronal, defined as the mechanism sound perception. The first is based on a number of acoustic patterns, the second - on the processes of reception and transformation of the mechanical energy of sound vibrations into bioelectric impulses and their transmission along nerve conductors to the auditory centers and cortical auditory nuclei. The organ of hearing is called the auditory, or sound, analyzer, whose function is based on the analysis and synthesis of non-verbal and verbal sound information containing natural and artificial sounds in the environment and speech symbols - words reflecting the material world and human mental activity. Hearing as a function of the sound analyzer is the most important factor in the intellectual and social development a person’s personality, for the perception of sound is the basis of his linguistic development and all his conscious activity.

Adequate stimulus of the sound analyzer

An adequate stimulus of a sound analyzer is understood as the energy of the audible range of sound frequencies (from 16 to 20,000 Hz), the carrier of which is sound waves. The speed of propagation of sound waves in dry air is 330 m/s, in water - 1430, in metals - 4000-7000 m/s. The peculiarity of the sound sensation is that it is extrapolated into the external environment in the direction of the sound source, this determines one of the main properties of the sound analyzer - ototopic, i.e. the ability to spatially distinguish the localization of a sound source.

The main characteristics of sound vibrations are their spectral composition And energy. The sound spectrum can be solid, when the energy of sound vibrations is evenly distributed over its constituent frequencies, and ruled, when the sound consists of a collection of discrete (intermittent) frequency components. Subjectively, a sound with a continuous spectrum is perceived as noise without a specific tonal coloring, for example, like the rustling of leaves or the “white” noise of an audiometer. Line spectrum The sounds produced by musical instruments and the human voice have multiple frequencies. Such sounds are dominated by fundamental frequency, which determines pitch(tone), and the set of harmonic components (overtones) determines sound timbre.

The energy characteristic of sound vibrations is the unit of sound intensity, which is defined as energy transferred by a sound wave through a unit surface area per unit time. The sound intensity depends on sound pressure amplitudes, as well as on the properties of the medium itself in which sound propagates. Under sound pressure understand the pressure that occurs when a sound wave passes through a liquid or gaseous medium. Propagating in a medium, a sound wave forms condensations and rarefactions of particles of the medium.

The SI unit of sound pressure is newton per 1 m 2. In some cases (for example, in physiological acoustics and clinical audiometry), the concept is used to characterize sound sound pressure level, expressed in decibels(dB), as the ratio of the magnitude of a given sound pressure R to sensory sound pressure threshold Ro= 2.10 -5 N/m 2. In this case, the number of decibels N= 20lg ( R/Ro). In air, sound pressure within the audible frequency range varies from 10 -5 N/m 2 near the threshold of audibility to 10 3 N/m 2 at the loudest sounds, for example, the noise produced by a jet engine. The subjective characteristic of hearing is associated with sound intensity - sound volume and many other qualitative characteristics of auditory perception.

The carrier of sound energy is a sound wave. Sound waves are understood as cyclical changes in the state of a medium or its disturbances, caused by the elasticity of a given medium, propagating in this medium and carrying with them mechanical energy. The space in which sound waves propagate is called the sound field.

The main characteristics of sound waves are wavelength, period, amplitude and speed of propagation. The concepts of sound radiation and its propagation are associated with sound waves. To emit sound waves, it is necessary to produce some disturbance in the medium in which they propagate due to an external source of energy, i.e., a sound source. The propagation of a sound wave is characterized primarily by the speed of sound, which, in turn, is determined by the elasticity of the medium, i.e., the degree of its compressibility, and density.

Sound waves propagating in a medium have the property attenuation, i.e., a decrease in amplitude. The degree of sound attenuation depends on its frequency and the elasticity of the medium in which it propagates. The lower the frequency, the lower the degree of attenuation, the further the sound travels. The absorption of sound by a medium increases noticeably with increasing frequency. Therefore, ultrasound, especially high-frequency ultrasound, and hypersound propagate over very short distances, limited to a few centimeters.

The laws of propagation of sound energy are inherent in the mechanism sound conduction in the organ of hearing. However, in order for sound to begin to spread along the chain of auditory ossicles, it is necessary that the eardrum begin to vibrate. The fluctuations of the latter arise as a result of its ability resonate, i.e., absorb the energy of sound waves incident on it.

Resonance is an acoustic phenomenon, as a result of which sound waves incident on any body cause forced oscillations of this body with the frequency of incoming waves. The closer natural frequency vibrations of the irradiated object to the frequency of the incident waves, the more sound energy this object absorbs, the higher the amplitude of its forced vibrations becomes, as a result of which this object itself begins to emit its own sound with a frequency equal to the frequency of the incident sound. The eardrum, due to its acoustic properties, has the ability to resonate across a wide range of sound frequencies with almost the same amplitude. This type of resonance is called blunt resonance.

Physiology of the sound conducting system

The anatomical elements of the sound conducting system are the auricle, external auditory canal, tympanic membrane, chain of auditory ossicles, muscles of the tympanic cavity, structures of the vestibule and cochlea (perilymph, endolymph, Reisner's, integumentary and basilar membranes, hairs of sensory cells, secondary tympanic membrane (cochlear window membrane) ). Figure 1 shows a general diagram of the sound transmission system.

Rice. 1. General diagram of the sound transmission system. The arrows show the direction of the sound wave: 1 - external auditory canal; 2 - supratympanic space; 3 - anvil; 4 - stirrup; 5 - head of the hammer; 6, 10 - scala vestibule; 7, 9 - cochlear duct; 8 - cochlear part of the vestibulocochlear nerve; 11 - scala tympani; 12 - auditory tube; 13 - window of the cochlea, covered by the secondary tympanic membrane; 14 - window of the vestibule, with the foot plate of the stapes

Each of these elements is characterized by specific functions, which together provide the process of primary processing of the sound signal - from its “absorption” by the eardrum to decomposition into frequencies by the structures of the cochlea and preparing it for reception. Removal of any of these elements from the process of sound transmission or damage to any of them leads to disruption of the transmission of sound energy, manifested by the phenomenon conductive hearing loss.

Auricle human has retained in a reduced form some useful acoustic functions. Thus, the sound intensity at the level of the external opening of the auditory canal is 3-5 dB higher than in a free sound field. The ears play a certain role in the implementation of the function ototopics And binaural hearing Ears They also play a protective role. Due to the special configuration and relief, when air flows over them, diverging vortex flows are formed, preventing air and dust particles from entering the ear canal.

Functional meaning external auditory canal should be considered in two aspects - clinical-physiological and physiological-acoustic. The first is determined by the fact that in the skin of the membranous part of the external auditory canal there are hair follicles, sebaceous and sweat glands, as well as special glands that produce earwax. These formations play a trophic and protective role, preventing penetration into the external auditory canal foreign bodies, insects, dust particles. Earwax, as a rule, is released in small quantities and is a natural lubricant for the walls of the external auditory canal. Being sticky in a “fresh” state, it promotes the adhesion of dust particles to the walls of the membranous-cartilaginous part of the external auditory canal. Drying, it fragments during the act of chewing under the influence of movements in the temporomandibular joint and together with exfoliating particles of the stratum corneum skin and foreign inclusions adhered to it are released out. Earwax has a bactericidal property, as a result of which no microorganisms are found on the skin of the external auditory canal and the eardrum. The length and curvature of the external auditory canal help protect the eardrum from direct injury from a foreign body.

The functional (physiological-acoustic) aspect is characterized by the role played by external auditory canal in conducting sound to the eardrum. This process is influenced not by the diameter of the existing or resulting narrowing of the ear canal, but by the length of this narrowing. Thus, with long narrow scar strictures, hearing loss at different frequencies can reach 10-15 dB.

Eardrum is a receiver-resonator of sound vibrations, which, as noted above, has the property of resonating in a wide range of frequencies without significant energy losses. Vibrations of the eardrum are transmitted to the handle of the malleus, then to the incus and stirrup. Vibrations of the foot plate of the stapes are transmitted to the perilymph of the scala vestibularis, which causes vibrations of the main and integumentary membranes of the cochlea. Their vibrations are transmitted to the hair apparatus of auditory receptor cells, in which mechanical energy is transformed into nerve impulses. Vibrations of the perilymph in the scala vestibularis are transmitted through the apex of the cochlea to the perilymph of the scala tympani and then vibrate the secondary tympanic membrane of the cochlear window, the mobility of which ensures the oscillatory process in the cochlea and protects the receptor cells from excessive mechanical stress during loud sounds.

Auditory ossicles combined into a complex lever system that provides increase in strength sound vibrations, necessary to overcome the resting inertia of the perilymph and endolymph of the cochlea and the frictional force of the perilymph in the ducts of the cochlea. The role of the auditory ossicles is also that they, by directly transmitting sound energy to the liquid media of the cochlea, prevent the reflection of the sound wave from the perilymph in the area of ​​the vestibular window.

The mobility of the auditory ossicles is ensured by three joints, two of which ( incus-hammer And anvil-stirrup) are arranged in a typical way. The third joint (the foot plate of the stapes in the window of the vestibule) is only a joint in function; in fact, it is a complex “flap” that performs a dual role: a) ensuring the mobility of the stapes necessary for transmitting sound energy to the structures of the cochlea; b) sealing of the ear labyrinth in the area of ​​the vestibular (oval) window. The element providing these functions is ring connective tissue ligament.

Muscles of the tympanic cavity(the tensor tympani muscle and the stapedius muscle) perform a dual function - protective against strong sounds and adaptive when it is necessary to adapt the sound-conducting system to weak sounds. They are innervated by motor and sympathetic nerves, which in some diseases (myasthenia, multiple sclerosis, various kinds of autonomic disorders) often affects the condition of these muscles and may manifest itself in hearing impairment that is not always identifiable.

It is known that the muscles of the tympanic cavity reflexively contract in response to sound stimulation. This reflex comes from receptors in the cochlea. If you apply sound to one ear, a friendly contraction of the muscles of the tympanic cavity occurs in the other ear. This reaction is called acoustic reflex and is used in some hearing research techniques.

There are three types of sound transmission: air, tissue and tube (i.e., through the auditory tube). Air type- this is natural sound conduction, caused by the flow of sound to the hair cells of the spiral organ from the air through the auricle, eardrum and the rest of the sound conduction system. Fabric, or bone, sound conduction is realized as a result of the penetration of sound energy to the moving sound-conducting elements of the cochlea through the tissues of the head. An example of the implementation of bone sound conduction is the tuning fork hearing test technique, in which the handle of a sounding tuning fork is pressed against the mastoid process, crown or other part of the head.

Distinguish compression And inertia mechanism tissue sound conduction. With the compression type, compression and discharge of the liquid media of the cochlea occurs, which causes irritation of the hair cells. With the inertial type, the elements of the sound conducting system, due to the inertial forces developed by their mass, lag behind the rest of the tissues of the skull in their vibrations, resulting in oscillatory movements in the liquid media of the cochlea.

The functions of intracochlear sound conduction include not only the further transmission of sound energy to the hair cells, but also primary spectral analysis sound frequencies, and their distribution among the corresponding sensory elements located on the basilar membrane. With this distribution, a peculiar acoustic-topical principle"cable" transmission nerve signal to the higher auditory centers, allowing for higher analysis and synthesis of information contained in sound messages.

Auditory reception

Auditory reception is understood as the transformation of the mechanical energy of sound vibrations into electrophysiological nerve impulses, which are a coded expression of an adequate stimulus of the sound analyzer. The receptors of the spiral organ and other elements of the cochlea serve as a generator of biocurrents called cochlear potentials. There are several types of these potentials: resting currents, action currents, microphone potential, summation potential.

Quiescent currents are registered in the absence of a sound signal and are divided into intracellular And endolymphatic potentials. Intracellular potential is recorded in nerve fibers, in hair and supporting cells, in the structures of the basilar and Reissner (reticular) membranes. Endolymphatic potential is recorded in the endolymph of the cochlear duct.

Action currents- these are interfered peaks of bioelectric impulses generated only by the fibers of the auditory nerve in response to sound exposure. The information contained in the action currents is in direct spatial dependence on the location of the neurons stimulated on the main membrane (the theories of hearing by Helmholtz, Bekesy, Davis, etc.). The auditory nerve fibers are grouped into channels, that is, based on their frequency throughput. Each channel is capable of transmitting only a signal of a certain frequency; Thus, if the cochlea is currently affected by low sounds, then only “low-frequency” fibers participate in the process of information transmission, and high-frequency fibers are at rest at this time, i.e., only spontaneous activity is recorded in them. When the cochlea is irritated by a prolonged monophonic sound, the frequency of discharges in individual fibers decreases, which is associated with the phenomenon of adaptation or fatigue.

Snail microphone effect is the result of a response to sound stimulation of only the outer hair cells. Action ototoxic substances And hypoxia lead to suppression or disappearance of the cochlea's microphone effect. However, there is also an anaerobic component in the metabolism of these cells, since the microphonic effect persists for several hours after the death of the animal.

Summation potential owes its origin to the response to sound of the inner hair cells. In the normal homeostatic state of the cochlea, the summation potential recorded in the cochlear duct retains its optimal negative sign, however, slight hypoxia, the action of quinine, streptomycin and a number of other factors that disrupt the homeostasis of the internal environments of the cochlea, disrupt the ratio of the magnitudes and signs of the cochlear potentials, at which the summation potential becomes positive.

By the end of the 50s. XX century it was found that in response to sound exposure, certain biopotentials arise in various structures of the cochlea, which give rise to the complex process of sound perception; in this case, action potentials (action currents) arise in the receptor cells of the spiral organ. Clinically, it seems very important fact the high sensitivity of these cells to oxygen deficiency, changes in the level of carbon dioxide and sugar in the liquid media of the cochlea, and disturbances in ionic balance. These changes can lead to parabiotic reversible or irreversible pathomorphological changes in the receptor apparatus of the cochlea and to corresponding disorders auditory function.

Otoacoustic emissions. The receptor cells of the spiral organ, in addition to their main function, have another amazing property. At rest or under the influence of sound, they come into a state of high-frequency vibration, resulting in the formation of kinetic energy that propagates as a wave process through the tissues of the inner and middle ear and is absorbed by the eardrum. The latter, under the influence of this energy, begins to emit, like a loudspeaker diffuser, a very weak sound in the range of 500-4000 Hz. Otoacoustic emission is not a process of synaptic (nervous) origin, but the result of mechanical vibrations of the hair cells of the spiral organ.

Psychophysiology of hearing

The psychophysiology of hearing considers two main groups of problems: a) measurement threshold of sensation, which is understood as the minimum limit of sensitivity of the human sensory system; b) construction psychophysical scales, reflecting the mathematical dependence or relationship in the “stimulus/response” system for various quantitative values ​​of its components.

There are two forms of sensation threshold - lower absolute threshold of sensation And upper absolute threshold of sensation. The first is understood the minimum magnitude of the stimulus that causes a response, at which for the first time a conscious sensation of a given modality (quality) of the stimulus arises(in our case - sound). By the second we mean the magnitude of the stimulus at which the sensation of a given modality of the stimulus disappears or changes qualitatively. For example, a powerful sound causes a distorted perception of its tonality or is even extrapolated into the area of ​​pain (“pain threshold”).

The magnitude of the sensation threshold depends on the degree of hearing adaptation at which it is measured. When adapting to silence, the threshold decreases; when adapting to a certain noise, it increases.

Subthreshold stimuli those whose magnitude does not cause adequate sensation and does not form sensory perception are called. However, according to some data, subthreshold stimuli, when applied for a sufficiently long time (minutes and hours), can cause “spontaneous reactions” such as causeless memories, impulsive decisions, sudden insights.

Associated with the threshold of sensation are the so-called discrimination thresholds: differential intensity (strength) threshold (DPI or DPS) and differential quality or frequency threshold (DFC). Both of these thresholds are measured as at sequential, and with simultaneous presentation of incentives. When stimuli are presented sequentially, the discrimination threshold can be set if the compared sound intensities and tonality differ by at least 10%. Simultaneous discrimination thresholds, as a rule, are established at the threshold detection of a useful (testing) sound against the background of interference (noise, speech, heteromodal). The method of determining simultaneous discrimination thresholds is used to study the noise immunity of an audio analyzer.

The psychophysics of hearing also considers thresholds of space, locations And time. The interaction of the sensations of space and time gives an integral sense of movement. The sense of movement is based on the interaction of the visual, vestibular and sound analyzers. The location threshold is determined by the spatiotemporal discreteness of the excited receptor elements. Thus, on the basement membrane, a sound of 1000 Hz is displayed approximately in the region of its middle part, and a sound of 1002 Hz is shifted towards the main helix so much that between the sections of these frequencies there is one unexcited cell for which “there was no” corresponding frequency. Therefore, theoretically, the sound location threshold is identical to the frequency discrimination threshold and is 0.2% in the frequency dimension. This mechanism provides an ototopic threshold extrapolated into space in the horizontal plane of 2-3-5°; in the vertical plane this threshold is several times higher.

The psychophysical laws of sound perception form the psychophysiological functions of the sound analyzer. The psychophysiological functions of any sensory organ are understood as the process of the emergence of a sensation specific to a given receptor system when an adequate stimulus acts on it. Psychophysiological methods are based on recording a person’s subjective response to a particular stimulus.

Subjective reactions The hearing organs are divided into two large groups - spontaneous And caused by. The former are close in quality to the sensations caused by real sound, although they arise “inside” the system, most often when the sound analyzer is tired, intoxicated, various local and common diseases. The evoked sensations are caused primarily by the action of an adequate stimulus within given physiological limits. However, they can be provoked by external pathogenic factors (acoustic or mechanical trauma to the ear or auditory centers), then these sensations are inherently close to spontaneous.

Sounds are divided into informational And indifferent. Often the latter serve as an obstacle to the former, therefore, in the auditory system there is, on the one hand, a mechanism for selecting useful information, and on the other, a mechanism for suppressing interference. Together they provide one of the most important physiological functions of the sound analyzer - noise immunity.

IN clinical studies Only a small part of psychophysiological methods for studying auditory function are used, which are based on only three: a) perception of intensity(strength) of sound, reflected in subjective sensation volume and in the differentiation of sounds by strength; b) frequency perception sound, reflected in the subjective feeling of tone and timbre of sound, as well as in the differentiation of sounds by tonality; V) perception of spatial localization sound source, reflected in the function of spatial hearing (ototopics). All of these functions interact in the natural habitat of humans (and animals), changing and optimizing the process of perception of sound information.

Psychophysiological indicators of hearing function, like any other sense organ, are based on one of the most important functions of complex biological systems - adaptation.

Adaptation is a biological mechanism by which the body or its individual systems adapt to the energy level of external or internal stimuli acting on them for adequate functioning in the process of their life activity. The process of adaptation of the hearing organ can be implemented in two directions: increased sensitivity to weak sounds or their absence and decreased sensitivity to excessively strong sounds. Increasing the sensitivity of the hearing organ in silence is called physiological adaptation. The restoration of sensitivity after its decrease, which occurs under the influence of long-acting noise, is called reverse adaptation. The time during which the sensitivity of the hearing organ returns to its original, higher level is called reverse adaptation time(BOA).

The depth of adaptation of the hearing organ to sound exposure depends on the intensity, frequency and duration of the sound, as well as on the time of adaptation testing and the ratio of the frequencies of the influencing and testing sounds. The degree of auditory adaptation is assessed by the magnitude of hearing loss above threshold and by BOA.

Masking is a psychophysiological phenomenon based on the interaction of testing and masking sounds. The essence of masking is that when two sounds of different frequencies are simultaneously perceived, the more intense (louder) sound will mask the weaker one. Two theories compete to explain this phenomenon. One of them gives preference to the neuronal mechanism of the auditory centers, finding confirmation that when exposed to noise in one ear, an increase in the sensitivity threshold in the other ear is observed. Another point of view is based on the peculiarities of the biomechanical processes occurring on the basilar membrane, namely during monoaural masking, when the testing and masking sounds are presented in one ear, lower sounds mask higher sounds. This phenomenon is explained by the fact that a “traveling wave” propagating along the basilar membrane from low sounds to the top of the cochlea absorbs similar waves generated from higher frequencies in the lower parts of the basilar membrane, and thus deprives the latter of its ability to resonate at high frequencies. Probably both of these mechanisms take place. The considered physiological functions of the hearing organ underlie all existing methods his research.

Spatial sound perception

Spatial perception of sound ( ototopics according to V.I. Voyachek) is one of the psychophysiological functions of the hearing organ, thanks to which animals and humans have the ability to determine the direction and spatial position of the sound source. The basis of this function is two-ear (binaural) hearing. Persons with one ear turned off are not able to navigate in space by sound and determine the direction of the sound source. In the clinic, ototopics is important in the differential diagnosis of peripheral and central lesions of the organ of hearing. When the cerebral hemispheres are damaged, various ototopic disorders occur. In the horizontal plane, the ototopic function is performed with greater accuracy than in the vertical plane, which confirms the theory about the leading role of binaural hearing in this function.

Hearing theories

The above psychophysiological properties of the sound analyzer are, to one degree or another, explained by a number of theories of hearing developed in the late 19th - early 20th centuries.

Helmholtz's resonance theory explains the emergence of tonal hearing by the phenomenon of resonating the so-called strings of the main membrane at different frequencies: short fibers of the main membrane located in the lower helix of the cochlea resonate to high sounds, fibers located in the middle helix of the cochlea resonate to medium frequencies, and to low frequencies in the upper helix , where the longest and most relaxed fibers are located.

Bekesy traveling wave theory is based on hydrostatic processes in the cochlea, which, with each oscillation of the foot plate of the stapes, causes deformation of the main membrane in the form of a wave running towards the apex of the cochlea. At low frequencies, the traveling wave reaches a section of the main membrane located at the apex of the cochlea, where the long “strings” are located; at high frequencies, the waves cause the main membrane to bend in the main helix, where the short “strings” are located.

Theory of P. P. Lazarev explains the spatial perception of individual frequencies along the main membrane by the unequal sensitivity of the hair cells of the spiral organ to different frequencies. This theory was confirmed in the works of K. S. Ravdonik and D. I. Nasonov, according to which living cells of the body, regardless of their affiliation, react with biochemical changes to sound irradiation.

Theories about the role of the main membrane in the spatial discrimination of sound frequencies have been confirmed in studies with conditioned reflexes in the laboratory of I. P. Pavlov. In these studies, a conditioned food reflex was developed to different frequencies, which disappeared after the destruction of different parts of the main membrane responsible for the perception of certain sounds. V.F. Undritz studied the biocurrents of the snail, which disappeared when various sections of the main membrane were destroyed.

Otorhinolaryngology. IN AND. Babiyak, M.I. Govorun, Ya.A. Nakatis, A.N. Pashchinin

ROSZHELDOR

Siberian State University

communication routes.

Department: “Life Safety”.

Discipline: “Human Physiology”.

Course work.

Topic: “Physiology of hearing.”

Option number 9.

Completed by: student Reviewed by: associate professor

gr. BTP-311 Rublev M. G.

Ostashev V. A.

Novosibirsk 2006

Introduction.

Our world is filled with sounds, the most diverse.

we hear all this, all these sounds are perceived by our ear. In the ear the sound turns into “machine gun fire”

nerve impulses that are transmitted along the auditory nerve to the brain.

Sound, or sound wave, is alternating rarefaction and condensation of air, spreading in all directions from a vibrating body. We hear such air vibrations with a frequency of 20 to 20,000 per second.

20,000 vibrations per second is the highest sound of the smallest instrument in the orchestra - the piccolo flute, and 24 vibrations is the sound of the lowest string - the double bass.

The idea that sound “flies into one ear and out the other” is absurd. Both ears do the same job, but do not communicate with each other.

For example: the ringing of a clock “flew” into your ear. He faces an instant, but rather complex journey to the receptors, that is, to those cells in which a sound signal is born under the action of sound waves. Having flown into the ear, the ringing will hit the eardrum.

The membrane at the end of the auditory canal is stretched relatively tightly and closes the passage tightly. The ringing, striking the eardrum, causes it to vibrate and vibrate. The stronger the sound, the more the membrane vibrates.

The human ear is a unique hearing device in terms of sensitivity.

The goals and objectives of this course work are to familiarize a person with the sense organs - hearing.

Talk about the structure and functions of the ear, as well as how to preserve hearing and how to deal with diseases of the hearing organ.

Also about various harmful factors at work that can damage hearing, and about measures to protect against such factors, since various diseases of the hearing organ can lead to more serious consequences - hearing loss and illness of the entire human body.

I. The importance of knowledge of hearing physiology for safety engineers.

Physiology is a science that studies the functions of the whole organism, individual systems and sensory organs. One of the sense organs is hearing. A safety engineer is required to know the physiology of hearing, since at his enterprise, as part of his duty, he comes into contact with the professional selection of persons, determining their suitability for this or that type of work, for this or that profession.

Based on data on the structure and function of the upper respiratory tract and ear, the question is decided in what type of production a person can work in and in which not.

Let's look at examples of several specialties.

Good hearing is necessary for people to control the operation of clock mechanisms, when testing motors and various equipment. Also, good hearing is necessary for doctors and drivers of various types of transport - land, rail, air, water.

The work of signalmen completely depends on the state of the auditory function. Radiotelegraph operators servicing radio communication and hydroacoustics devices involved in listening to underwater sounds or noise detection.

In addition to hearing sensitivity, they must also have a high perception of tone frequency differences. Radiotelegraph operators must have rhythmic hearing and memory for rhythm. Good rhythmic sensitivity is considered to be the error-free discrimination of all signals or no more than three errors. Unsatisfactory – if less than half of the signals are distinguished.

During the professional selection of pilots, parachutists, sailors, and submariners, it is very important to determine the barofunction of the ear and paranasal sinuses.

Barofunction is the ability to respond to pressure fluctuations external environment. And also have binaural hearing, that is, have spatial hearing and determine the position of the sound source in space. This property is based on the presence of two symmetrical halves of the auditory analyzer.

For fruitful and accident-free work, according to PTE and PTB, all persons in the above-mentioned specialties must undergo a medical commission to determine their ability to work in a given area, as well as for occupational safety and health.

II . Anatomy of the hearing organs.

The hearing organs are divided into three sections:

1. Outer ear. The external ear contains the external auditory canal and the pinna with muscles and ligaments.

2. Middle ear. The middle ear contains the eardrum, mastoid appendages and the auditory tube.

3. Inner ear. The inner ear contains the membranous labyrinth, which is located in the bony labyrinth inside the pyramid of the temporal bone.

Outer ear.

The auricle is an elastic cartilage of complex shape, covered with skin. Its concave surface faces forward, the lower part - the lobule of the auricle - the lobe, is devoid of cartilage and filled with fat. On the concave surface there is an antihelix, in front of it there is a depression - the concha of the ear, at the bottom of which there is an external auditory opening limited in front by the tragus. The external auditory canal consists of cartilaginous and bone sections.

The eardrum separates the outer ear from the middle ear. It is a plate consisting of two layers of fibers. The outer fibers are arranged radially, and the inner fibers are circular.

In the center of the eardrum there is a depression - the navel - the place where one of the auditory ossicles - the malleus - is attached to the eardrum. The tympanic membrane is inserted into the groove of the tympanic part of the temporal bone. The membrane is divided into an upper (smaller) free, unstretched part and a lower (larger) tense part. The membrane is located obliquely relative to the axis of the auditory canal.

Middle ear.

The tympanic cavity is air-filled, located at the base of the pyramid of the temporal bone, the mucous membrane is lined with single-layer squamous epithelium, which turns into cubic or cylindrical.

The cavity contains three auditory ossicles, tendons of the muscles that stretch the tympanic membrane and the stapes. The chorda tympani, a branch of the intermediate nerve, also passes here. The tympanic cavity passes into the auditory tube, which opens in the nasal part of the pharynx with the pharyngeal opening of the auditory tube.

The cavity has six walls:

1. The upper - tegmental wall separates the tympanic cavity from the cranial cavity.

2. The lower - jugular wall separates the tympanic cavity from the jugular vein.

3. Median - labyrinthine wall separates the tympanic cavity from the bony labyrinth of the inner ear. It has a window of the vestibule and a window of the cochlea, leading to the sections of the bony labyrinth. The window of the vestibule is closed by the base of the stapes, the window of the cochlea is closed by the secondary tympanic membrane. Above the window of the vestibule, the wall of the facial nerve protrudes into the cavity.

4. Literal - the membranous wall is formed by the tympanic membrane and the surrounding parts of the temporal bone.

5. The anterior - carotid wall separates the tympanic cavity from the canal of the internal carotid artery, and the tympanic opening of the auditory tube opens on it.

6. In the area of ​​the posterior mastoid wall there is an entrance to the mastoid cave; below it there is a pyramidal eminence, inside which the stapedius muscle begins.

The auditory ossicles are the stirrup, incus and malleus.

They are named so due to their shape - the smallest in the human body, they form a chain connecting the eardrum with the window of the vestibule leading to the inner ear. The ossicles transmit sound vibrations from the eardrum to the window of the vestibule. The handle of the hammer is fused to the eardrum. The head of the malleus and the body of the incus are connected to each other by a joint and strengthened by ligaments. The long process of the incus articulates with the head of the stapes, the base of which enters the window of the vestibule, connecting to its edge through the annular ligament of the stapes. The bones are covered with a mucous membrane.

The tendon of the tensor tympani muscle is attached to the handle of the malleus, and the stapedius muscle is attached to the stapes near its head. These muscles regulate the movement of the bones.

The auditory tube (Eustachian tube), about 3.5 cm long, performs a very important function - it helps to equalize the air pressure inside the tympanic cavity in relation to the external environment.

Inner ear.

The inner ear is located in the temporal bone. In the bone labyrinth, lined from the inside with periosteum, lies the membranous labyrinth, repeating the shape of the bone labyrinth. Between both labyrinths there is a gap filled with perilymph. The walls of the bone labyrinth are formed by compact bone tissue. It is located between the tympanic cavity and the internal auditory canal and consists of the vestibule, three semicircular canals and the cochlea.

The bony vestibule is an oval cavity communicating with the semicircular canals; on its wall there is a window of the vestibule, at the beginning of the cochlea there is a window of the cochlea.

The three bony semicircular canals lie in three mutually perpendicular planes. Each semicircular canal has two legs, one of which expands before entering the vestibule, forming an ampulla. The adjacent pedicles of the anterior and posterior canals are connected to form a common bony pedicle, so the three canals open into the vestibule with five openings. The bony cochlea forms 2.5 turns around a horizontally lying rod - a spindle, around which a bone spiral plate is twisted like a screw, pierced by thin canaliculi, where the fibers of the cochlear part of the vestibulocochlear nerve pass. At the base of the plate there is a spiral canal in which lies the spiral node - the organ of Corti. It consists of many fibers stretched like strings.

The ear is the organ of hearing and balance. Its components ensure the reception of sounds and the maintenance of balance.

Hearing irritant – mechanical energy in the form of sound vibrations, which are alternating condensations and rarefactions of air, propagating in all directions from the sound source at a speed of about 330 m/sec. Sound can travel through air, water and solids. The speed of propagation depends on the elasticity and density of the medium.

The auditory analyzer consists of:

1. Peripheral department– it includes the outer, middle and inner ear (Fig. 25);

2. Subcortical department– consists of the striatum of the pons (4th ventricle of the brain), the inferior colliculi of the midbrain, the medial (middle) geniculate body, and the thalamus.

3. Auditory zone cerebral cortex, located in the temporal region.

Outer ear. Function - capturing sounds and conducting them to the eardrum. It consists of the auricle, built of cartilaginous tissue, and the external auditory canal, which extends to the middle ear and is rich in glands that secrete earwax, which accumulates in the outer ear and from which dust and dirt are removed. The external auditory canal is up to 2.5 cm long and about 1 cm 3 wide. At the border between the outer and middle ear, the eardrum is stretched. Its thickness in humans is about

The auricle collects sound waves. Due to the fact that the size of the auricle is 3 times larger than the eardrum, the sound pressure on the latter is 3 times greater than on the auricle. The eardrum has elasticity, so it resists the pressure wave, which contributes to the rapid attenuation of its vibrations, and it perfectly transmits sound pressure, almost without distorting the shape of the sound wave.

Middle ear represented by a tympanic cavity of irregular shape and a capacity of 0.75 cm 3, located inside the temporal bone. It communicates with the nasopharynx using the auditory (Eustachian) tube and has a chain of articulated small bones - the malleus, incus and stapes, which transmit accurately and amplified vibrations of the eardrum to the thin oval plate in the inner ear.

The ossicular system increases the pressure of the sound wave when transmitted from the eardrum to the membrane of the oval window approximately 60-70 times. This amplification of sound occurs as a result of the fact that the surface of the eardrum (70 mm2) is 22-25 times larger than the surface of the stapes (3.2 mm2) attached to the oval window, therefore the sound increases by 22-25 times. Since the lever apparatus of the ossicles reduces the amplitude of sound waves by approximately 2.5 times, the same increase in the shock waves of sound waves on the oval window occurs, and the overall sound amplification is obtained by multiplying 22-25 by 2.5. The outer and middle ears conduct sound pressure, reducing the vibrations of the sound wave. Thanks to eustachian tube equal pressure is maintained on both sides of the eardrum. This pressure is equalized during swallowing movements.

The only way for air to enter and exit the middle ear is through Eustachian tube- a canal that goes to the back of the nasal cavity and communicates with the nasopharynx. Thanks to this channel, the air pressure in the middle ear is equalized with atmospheric pressure, and thus the air pressure on the eardrum is equalized. When flying on an airplane, your ears become blocked when climbing or descending. This is due to a sharp change in atmospheric pressure, which causes the eardrum to sag. Then a yawn or simple swallowing of saliva leads to the opening of the valve located in the Eustachian tube, and the pressure in the middle ear is equalized with atmospheric pressure; at the same time, the eardrum returns to its normal position and the ears “open”.

Antipyretics for children are prescribed by a pediatrician. But there are situations emergency care for fever, when the child needs to be given medicine immediately. Then the parents take responsibility and use antipyretic drugs.

What is allowed to be given to infants? How can you lower the temperature in older children? What medications are the safest? The process of obtaining sound information includes the perception, transmission and interpretation of sound. The ear catches and transforms auditory waves

There is a lot in the ear that is not visible to the eye. What we observe is only part of the outer ear - a fleshy-cartilaginous outgrowth, in other words, the auricle. The outer ear consists of the concha and the ear canal, ending at the eardrum, which provides communication between the outer and middle ear, where the hearing mechanism is located.

Auricle directs sound waves into the ear canal, similar to how the ancient Eustachian trumpet directed sound into the pinna. The channel amplifies sound waves and directs them to eardrum. Sound waves hitting the eardrum cause vibrations that are transmitted through three small auditory bones: the malleus, the incus and the stapes. They vibrate in turn, transmitting sound waves through the middle ear. The innermost of these bones, the stapes, is the smallest bone in the body.

Stapes, vibrating, strikes a membrane called the oval window. Sound waves travel through it to the inner ear.

What happens in the inner ear?

There is a sensory part of the auditory process. Inner ear consists of two main parts: the labyrinth and the snail. The part, which starts at the oval window and curves like a real cochlea, acts as a translator, turning sound vibrations into electrical impulses that can be transmitted to the brain.

How does a snail work?

Snail filled with liquid, in which the basilar (main) membrane seems to be suspended, resembling a rubber band, attached at its ends to the walls. The membrane is covered with thousands of tiny hairs. At the base of these hairs are small nerve cells. When the vibrations of the stapes touch the oval window, the fluid and hairs begin to move. The movement of the hairs stimulates nerve cells, which send a message, in the form of an electrical impulse, to the brain through the auditory, or acoustic, nerve.

Labyrinth is a group of three interconnected semicircular canals that control the sense of balance. Each channel is filled with liquid and located at right angles to the other two. So, no matter how you move your head, one or more channels record that movement and transmit the information to the brain.

If you have ever had a cold in your ear or blown your nose too much, so that your ear “clicks”, then a guess arises: the ear is somehow connected with the throat and nose. And that's true. Eustachian tube directly connects the middle ear to the oral cavity. Its role is to allow air into the middle ear, balancing the pressure on both sides of the eardrum.

Impairments and disorders in any part of the ear can impair hearing if they affect the passage and interpretation of sound vibrations.

How does the ear work?

Let's trace the path of the sound wave. It enters the ear through the pinna and is directed through the auditory canal. If the concha is deformed or the canal is blocked, the path of sound to the eardrum is hampered and hearing ability is reduced. If the sound wave successfully reaches the eardrum, but it is damaged, the sound may not reach the auditory ossicles.

Any disorder that prevents the ossicles from vibrating will prevent sound from reaching the inner ear. In the inner ear, sound waves cause fluid to pulsate, moving tiny hairs in the cochlea. Damage to the hairs or the nerve cells to which they are connected will prevent the sound vibrations from being converted into electrical vibrations. But when the sound has successfully turned into an electrical impulse, it still has to reach the brain. It is clear that damage to the auditory nerve or brain will affect the ability to hear.

Why do such disorders and damage occur?

There are many reasons, we will discuss them later. But the most common culprits are foreign objects in the ear, infections, ear diseases, other diseases that cause complications in the ears, head injuries, ototoxic (i.e. poisonous to the ear) substances, changes in atmospheric pressure, noise, age-related degeneration. All of this causes two main types of hearing loss.

Topic 15. PHYSIOLOGY OF THE AUDITORY SYSTEM.

Auditory system- one of the most important distant sensory systems of a person in connection with the emergence of speech as a means of communication. Her function consists in the formation of a person’s auditory sensations in response to the action of acoustic (sound) signals, which are air vibrations with different frequencies and strengths. A person hears sounds that are in the range from 20 to 20,000 Hz. It is known that many animals have a much wider range of audible sounds. For example, dolphins “hear” sounds with a frequency of up to 170,000 Hz. But the human auditory system is designed primarily to hear the speech of another person, and in this respect its excellence cannot be even closely compared with the auditory systems of other mammals.

The human auditory analyzer consists of

1) peripheral part(outer, middle and inner ear);

2) auditory nerve;

3) central sections (cochlear nuclei and superior olive nuclei, posterior colliculus, internal geniculate body, auditory cortex).

In the outer, middle and inner ear the processes necessary for auditory perception occur. preparatory processes, the meaning of which is to optimize the parameters of transmitted sound vibrations while maintaining the nature of the signals. In the inner ear, the energy of sound waves is converted into receptor potentials hair cells.

Outer ear includes the auricle and external auditory canal. The topography of the auricle plays a significant role in the perception of sounds. If, for example, this relief is destroyed by filling it with wax, a person is noticeably less able to determine the direction of the sound source. The average human external auditory canal is about 9 cm long. There is evidence that a tube of this length and similar diameter has a resonance at a frequency of about 1 kHz, in other words, sounds of this frequency are slightly amplified. The middle ear is separated from the outer ear by the tympanic membrane, which has the shape of a cone with the apex facing the tympanic cavity.

Rice. Auditory sensory system

Middle ear filled with air. It contains three bones: malleus, incus and stapes, which sequentially transmit vibrations of the eardrum to the inner ear. The hammer is woven into the eardrum with a handle; its other side is connected to the anvil, which transmits vibrations to the stapes. Due to the peculiarities of the geometry of the auditory ossicles, vibrations of the eardrum of reduced amplitude but increased strength are transmitted to the stapes. In addition, the surface of the stapes is 22 times smaller than the eardrum, which increases its pressure on the oval window membrane by the same amount. As a result of this, even weak sound waves acting on the eardrum can overcome the resistance of the membrane of the oval window of the vestibule and lead to vibrations of the fluid in the cochlea. Favorable conditions for vibrations of the eardrum are also created by Eustachian tube, connecting the middle ear with the nasopharynx, which serves to equalize the pressure in it with atmospheric pressure.

In the wall separating the middle ear from the inner ear, in addition to the oval one, there is also a round window of the cochlea, also closed by a membrane. Fluctuations of the cochlear fluid, which arose at the oval window of the vestibule and passed along the passages of the cochlea, reach, without damping, the round window of the cochlea. In its absence, due to the incompressibility of the liquid, its vibrations would be impossible.

There are also two small muscles in the middle ear - one attached to the handle of the malleus and the other to the stapes. Contraction of these muscles prevents the ossicles from vibrating too much due to loud noises. This is the so-called acoustic reflex. The main function of the acoustic reflex is to protect the cochlea from damaging stimulation..

Inner ear. There is a complex shaped cavity in the pyramid of the temporal bone (bone labyrinth), the components of which are the vestibule, cochlea and semicircular canals. It includes two receptor apparatus: vestibular and auditory. The auditory part of the labyrinth is the cochlea, which is a spiral of two and a half curls twisted around a hollow bone spindle. Inside the bone labyrinth, as if in a case, there is a membranous labyrinth, the shape corresponding to the bone labyrinth. The vestibular system will be discussed in the next topic.

Let's describe the auditory organ. The bony canal of the cochlea is divided by two membranes - the main, or basilar, And Reisner's or vestibular - into three separate canals, or scalae: tympanic, vestibular and middle (membranous cochlear canal). The canals of the inner ear are filled with liquids, the ionic composition of which is specific in each canal. The middle scala is filled with endolymph with a high content of potassium ions. The other two staircases are filled with perilymph, the composition of which does not differ from tissue fluid. The vestibular and tympanic scalae at the top of the cochlea are connected through a small opening - the helicotrema; the middle scala ends blindly.

Located on the basilar membrane organ of corti, consisting of several rows of hair receptor cells supported by supporting epithelium. About 3,500 hair cells form the inner row (inner hair cells), and approximately 12-20 thousand outer hair cells form three, and in the region of the apex of the cochlea, five longitudinal rows. On the surface of the hair cells facing inward, there are sensitive hairs covered with a plasma membrane - stereocilia. Hairs are connected to the cytoskeleton, their mechanical deformation leads to the opening of membrane ion channels and the emergence of a receptor potential in hair cells. Above the organ of Corti there is a jelly-like cover (tectorial) membrane, formed by glycoprotein and collagen fibers and attached to the inner wall of the labyrinth. Tips of stereocilia outer hair cells are immersed in the substance of the integumentary plate.

The middle scala, filled with endolymph, is positively charged (up to +80 mV) relative to the other two scalae. If we take into account that the resting potential of individual hair cells is about -80 mV, then in general the potential difference ( endocochlear potential) in the area of ​​the middle scala - the organ of Corti can be about 160 mV. The endocochlear potential plays an important role in the excitation of hair cells. It is assumed that hair cells are polarized by this potential up to critical level. Under these conditions, minimal mechanical influences can cause excitation of the receptor.

Neurophysiological processes in the organ of Corti. The sound wave acts on the eardrum, and then through the ossicular system the sound pressure is transmitted to the oval window and affects the perilymph of the scala vestibule. Since the fluid is incompressible, the movement of perilymph can be transmitted through the helicotrema to the scala tympani, and from there through the round window back to the middle ear cavity. Perilymph can also move in a shorter way: Reisner's membrane bends, and through the middle scala the pressure is transferred to the main membrane, then to the scala tympani and through the round window into the cavity of the middle ear. Exactly at the latter case auditory receptors are stimulated. Vibrations of the main membrane lead to displacement of the hair cells relative to the integumentary membrane. When the stereocilia of hair cells are deformed, a receptor potential arises in them, which leads to the release of a mediator glutamate. By acting on the postsynaptic membrane of the afferent ending of the auditory nerve, the mediator causes the generation of an excitatory postsynaptic potential in it and then the generation of impulses propagating to the nerve centers.

The Hungarian scientist G. Bekesi (1951) proposed "travelling wave theory" allowing us to understand how a sound wave of a certain frequency excites hair cells located in a certain place in the main membrane. This theory received universal recognition. The main membrane expands from the base of the cochlea to its apex approximately 10 times (in humans, from 0.04 to 0.5 mm). It is assumed that the main membrane is fixed only along one edge, the rest of it slides freely, which corresponds to the morphological data. Bekesy's theory explains the mechanism of sound wave analysis as follows: high-frequency vibrations travel only a short distance across the membrane, while long waves travel far. Then the initial part of the main membrane serves as a high-frequency filter, and long waves travel all the way to the helicotrema. Maximum movements for different frequencies occur at different points of the main membrane: the lower the tone, the closer its maximum is to the apex of the cochlea. Thus, the pitch of a sound is encoded by a location on the main membrane. This is the structural and functional organization of the receptor surface of the main membrane. is defined as tonotopic.

Rice. Tonotopic diagram of the cochlea

Physiology of pathways and centers of the auditory system. 1st order neurons (bipolar neurons) are located in the spiral ganglion, which is located parallel to the organ of Corti and follows the curls of the cochlea. One branch of the bipolar neuron forms a synapse on the auditory receptor, and the other goes to the brain, forming the auditory nerve. The auditory nerve fibers leave the internal auditory canal and reach the brain in the area of ​​the so-called cerebellopontine angle or lateral angle of the rhomboid fossa(this is the anatomical boundary between the medulla oblongata and the pons).

Neurons of the 2nd order form a complex of auditory nuclei in the medulla oblongata(ventral and dorsal). Each of them has a tonotopic organization. Thus, the frequency projection of the organ of Corti is generally repeated in an orderly manner in the auditory nuclei. The axons of the neurons of the auditory nuclei ascend into the overlying structures of the auditory analyzer both ipsi- and contralaterally.

The next level of the auditory system is at the level of the bridge and is represented by the nuclei of the superior olive (medial and lateral) and the nucleus of the trapezius body. At this level, binaural (from both ears) analysis of sound signals is already carried out. The projections of the auditory pathways to the indicated pontine nuclei are also organized tonotopically. Most neurons of the superior olive nuclei are excited binaural. With binaural hearing, the human sensory system detects sound sources that are away from the midline because sound waves hit the ear closest to that source first. Two categories of binaural neurons have been discovered. Some are excited by sound signals from both ears (BB-type), others are excited by one ear, but inhibited by the other (BT-type). The existence of such neurons provides a comparative analysis of sound signals arising on the left or right side of a person, which is necessary for his spatial orientation. Some neurons of the superior olive nuclei are most active when the timing of signals from the right and left ears diverges, while other neurons respond most strongly to different signal intensities.

Trapezoid nucleus receives predominantly a contralateral projection from the auditory nuclei complex, and in accordance with this, neurons respond predominantly to sound stimulation of the contralateral ear. Tonotopy is also found in this nucleus.

The axons of the cells of the auditory nuclei of the bridge are part of lateral loop. The main part of its fibers (mainly from the olive) switches in the inferior colliculus, the other part goes to the thalamus and ends on the neurons of the internal (medial) geniculate body, as well as in the superior colliculus.

Inferior colliculus, located on the dorsal surface of the midbrain, is the most important center for the analysis of sound signals. At this level, apparently, the analysis of sound signals necessary for indicative reactions to sound ends. The axons of the cells of the posterior colliculus are directed as part of its handle to the medial geniculate body. However, some of the axons go to the opposite hill, forming the intercalicular commissure.

Medial geniculate body, belonging to the thalamus, is the last switching nucleus of the auditory system on the way to the cortex. Its neurons are located tonotopically and form a projection into the auditory cortex. Some neurons in the medial geniculate body are activated in response to the onset or end of a signal, while others respond only to its frequency or amplitude modulations. The internal geniculate body contains neurons that can gradually increase activity when the same signal is repeated repeatedly.

Auditory cortex represents the highest center of the auditory system and is located in temporal lobe. In humans, it includes fields 41, 42 and partially 43. In each of the zones there is tonotopy, that is, a complete representation of the receptor apparatus of the organ of Corti. The spatial representation of frequencies in the auditory areas is combined with the columnar organization of the auditory cortex, especially pronounced in the primary auditory cortex (field 41). IN primary auditory cortex cortical columns are located tonotopically for separate processing of information about sounds of different frequencies in the auditory range. They also contain neurons that selectively respond to sounds of varying duration, to repeated sounds, to noise with a wide frequency range, etc. In the auditory cortex, information about the pitch and its intensity, and about the time intervals between individual sounds, is combined.

Following the stage of registration and combination of elementary features sound stimulus which is carried out simple neurons, are included in information processing complex neurons, selectively responding only to a narrow range of frequency or amplitude modulations of sound. This specialization of neurons allows the auditory system to create holistic auditory images, with combinations of elementary components of the auditory stimulus that are characteristic only for them. Such combinations can be recorded by memory engrams, which later makes it possible to compare new acoustic stimuli with previous ones. Certain complex neurons in the auditory cortex fire most strongly in response to human speech sounds.

Frequency-threshold characteristics of neurons of the auditory system. As described above, all levels of the mammalian auditory system have a tonotopic principle of organization. Another important characteristic of the neurons of the auditory system is the ability to selectively respond to a specific pitch of sound.

All animals have a correspondence between the frequency range of sounds produced and the audiogram, which characterizes the sounds heard. The frequency selectivity of neurons in the auditory system is described by a frequency-threshold curve (FTC), which reflects the dependence of the neuron response threshold on the frequency of the tonal stimulus. The frequency at which the excitation threshold of a given neuron is minimal is called the characteristic frequency. The FPC of auditory nerve fibers has a V-shape with one minimum, which corresponds to the characteristic frequency of a given neuron. The TPC of the auditory nerve has a noticeably sharper tuning compared to the amplitude-frequency curves of the main membranes). It is assumed that the exacerbation of the frequency-threshold curve involves efferent influences already at the level of auditory receptors (hair receptors are secondary sensory and receive efferent fibers).

Sound intensity coding. The intensity of the sound is encoded by the firing rate and the number of neurons fired. Therefore they believe that Impulse flux density is a neurophysiological correlate of loudness. The increase in the number of excited neurons under the influence of increasingly loud sounds is due to the fact that the neurons of the auditory system differ from each other in response thresholds. When the stimulus is weak, only a small number of the most sensitive neurons are involved in the reaction, and when the sound intensifies, an increasing number of additional neurons with higher reaction thresholds are involved in the reaction. In addition, the thresholds for excitation of internal and external receptor cells are not the same: excitation of internal hair cells occurs at a greater sound intensity, therefore, depending on its intensity, the ratio of the number of excited internal and external hair cells changes depending on its intensity.

In the central parts of the auditory system, neurons have been found that have a certain selectivity to sound intensity, i.e. responding to a fairly narrow range of sound intensity. Neurons with such a reaction first appear at the level of the auditory nuclei. At higher levels of the auditory system their number increases. The range of intensities they emit narrows, reaching minimum values ​​in cortical neurons. It is assumed that this specialization of neurons reflects the sequential analysis of sound intensity in the auditory system.

Subjectively perceived sound volume depends not only on the sound pressure level, but also on the frequency of the sound stimulus. The sensitivity of the auditory system is maximum for stimuli with frequencies from 500 to 4000 Hz; at other frequencies it decreases.

Binaural hearing. Humans and animals have spatial hearing, i.e. the ability to determine the position of a sound source in space. This property is based on the presence binaural hearing, or listening with two ears. The acuity of binaural hearing in humans is very high: the position of the sound source is determined with an accuracy of 1 angular degree. The basis for this is the ability of neurons in the auditory system to evaluate interaural (inter-ear) differences in the time of arrival of sound to the right and left ear and the intensity of sound in each ear. If the sound source is located away from the midline of the head, the sound wave arrives at one ear slightly earlier and has greater strength than at the other ear. Assessing the distance of a sound source from the body is associated with a weakening of the sound and a change in its timbre.

When the right and left ears are stimulated separately via headphones, a delay between sounds of as little as 11 µs or a 1 dB difference in the intensity of the two sounds results in an apparent shift in the localization of the sound source from the midline towards an earlier or stronger sound. The auditory centers contain neurons that are acutely tuned to a specific range of interaural differences in time and intensity. Cells have also been found that respond only to a certain direction of movement of a sound source in space.

Sound can be represented as oscillatory movements of elastic bodies propagating in various media in the form of waves. To perceive sound signaling, a receptor organ has been formed that is even more complex than the vestibular one. It was formed together with the vestibular apparatus, and therefore there are many similar structures in their structure. The bony and membranous canals in humans form 2.5 turns. The auditory sensory system for humans is second only to vision in terms of importance and volume of information received from the external environment.

Receptors of the auditory analyzer belong to secondly sensitive. Receptor hair cells(they have an abbreviated kinocilium) form a spiral organ (cortis), which is located in the helix of the inner ear, in its convoluted strand on the main membrane, the length of which is about 3.5 cm. It consists of 20,000-30,000 fibers (Fig. 159 ). Starting from the oval foramen, the length of the fibers gradually increases (about 12 times), while their thickness gradually decreases (about 100 times).

The formation of the spiral organ is completed by the tectorial membrane (covering membrane), located above the hair cells. There are two types of receptor cells located on the main membrane: internal- in one row, and external- at 3-4. On their membrane, returned to the side of the integumentary membrane, the inner cells have 30 - 40 relatively short (4-5 μm) hairs, and the outer cells have 65 - 120 thinner and longer ones. There is no functional equality between individual receptor cells. This is also evidenced by the morphological characteristics: a relatively small (about 3,500) number of internal cells provides 90% of the afferents of the cochlear (cochlear) nerve; while only 10% of neurons arise from the 12,000-20,000 outer cells. In addition, basal cells and

Rice. 159. 1 - adjustment ladder; 2 - drum ladders; WITH- main membrane; 4 - spiral organ; 5 - medium stairs; 6 - vascular strip; 7 - integumentary membrane; 8 - Reisner's membrane

especially the middle, helix and whorl have more nerve endings than the apical helix.

The space of the spiral strait is filled endolymph. Above the vestibular and main membranes in the space of the corresponding channels contains perilymph. It is combined not only with the perilymph of the vestibular canal, but also with the subarachnoid space of the brain. Its composition is quite similar to that of cerebrospinal fluid.

Mechanism for transmitting sound vibrations

Before reaching the inner ear, sound vibrations pass through the outer and middle ears. The outer ear serves primarily to capture sound vibrations and maintain constant humidity and temperature of the eardrum (Fig. 160).

The cavity of the middle ear begins behind the eardrum and is closed at the other end by the membrane of the foramen ovale. The air-filled cavity of the middle ear is connected to the cavity of the nasopharynx using auditory (Eustachian) tube, serves to equalize pressure on both sides of the eardrum.

The eardrum, perceiving sound vibrations, transmits them to the system located in the middle ear ankles(hammer, incus and stapes). The bones not only send vibrations to the oval membrane, but also amplify the vibrations of the sound wave. This occurs due to the fact that the vibrations are first transmitted to a longer lever formed by the handle of the hammer and the process of the hammer. This is also facilitated by the difference in stirrup surfaces (about 3.2 o МҐ6 m2) and eardrum (7 * 10"6). The last circumstance approximately 22 times (70:3.2) increases the pressure of the sound wave on the drum

Rice. 160.: 1 - air transmission; 2 - mechanical transmission; 3 - liquid transmission; 4 - electric transmission

retina. But as the vibration of the eardrum increases, the amplitude of the wave decreases.

The above and subsequent sound transmission structures create an extremely high sensitivity of the auditory analyzer: sound is perceived even if the pressure on the eardrum is more than 0.0001 mg1cm2. In addition, the curl membrane moves a distance less than the diameter of the hydrogen atom.

The role of the muscles of the middle ear.

The muscles located in the cavity of the middle ear (m. tensor timpani and m. stapedius), influencing the tension of the eardrum and limiting the amplitude of movement of the stapes, participate in reflex adaptation auditory organ to sound intensity.

Powerful sound can lead to undesirable consequences both for the hearing system (up to damage to the eardrum and hairs of receptor cells, disruption of microcirculation in the helix) and for the central nervous system. Therefore, to prevent these consequences, the tension of the eardrum reflexively decreases. As a result, on the one hand, the possibility of its traumatic rupture, and on the other hand, the intensity of vibration of the bones and the structures of the inner ear located behind them decreases. Reflex muscle reaction observed within 10 ms from the onset of the powerful sound, which turns out to be 30-40 dB during the sound. This reflex closes at the level stem parts of the brain. In some cases, the air wave is so powerful and fast (for example, during an explosion) that the protective mechanism does not have time to work and various hearing damage occurs.

The mechanism of perception of sound vibrations by receptor cells of the inner ear

Vibrations of the membrane of the oval window are first transmitted to the peri-lymph of the vestibular scales, and then through the vestibular membrane to the endolymph (Fig. 161). At the apex of the cochlea, between the superior and inferior membranous canals, there is a connecting opening - helicotrema, through which the vibration is transmitted perilymph of scala tympani. In the wall separating the middle ear from the inner ear, in addition to the oval one, there is also round hole with its membrane.

The occurrence of a wave leads to the movement of the basilar and integumentary membranes, after which the hairs of the receptor cells that touch the integumentary membrane are deformed, causing the emergence of RP. Although the hairs of the inner hair cells touch the integumentary membrane, they also bend under the influence of displacements of the endolymph in the space between it and the tips of the hair cells.

Rice. 161.

Afferents of the cochlear nerve are associated with receptor cells, the transmission of impulses to which is mediated by a mediator. The main sensory cells of the organ of Corti, which determine the generation of APs in the auditory nerves, are the inner hair cells. The outer hair cells are innervated by cholinergic efferent nerve fibers. These cells become shorter in case of depolarization and elongate in case of hyperpolarization. They hyperpolarize under the influence of acetylcholine, which releases efferent nerve fibers. The function of these cells is to increase the amplitude and sharpen the vibration peaks of the basilar membrane.

Even in silence, the auditory nerve fibers conduct up to 100 impulses per second (background impulses). Deformation of the hairs leads to an increase in the permeability of cells to Na+, as a result of which the frequency of impulses in the nerve fibers extending from these receptors increases.

Pitch discrimination

The main characteristics of a sound wave are the frequency and amplitude of vibrations, as well as the exposure time.

The human ear is capable of perceiving sound when air vibrates in the range from 16 to 20,000 Hz. However, the greatest sensitivity is between 1000 and 4000 Hz, which is the range of the human voice. It is here that the sensitivity of hearing is similar to the level of Brownian noise - 2 * 10"5. Within the area of ​​auditory perception, a person can experience about 300,000 sounds of different strength and height.

It is assumed that there are two mechanisms for distinguishing pitches. A sound wave is a vibration of air molecules that travels in the form of a longitudinal pressure wave. Transmitted to the periendolimph, this wave that runs between the place of origin and attenuation has a section where the oscillations are characterized by maximum amplitude (Fig. 162).

The location of this amplitude maximum depends on the vibration frequency: in the case of high frequencies it is closer to the oval membrane, and in the case of lower frequencies it is closer to the helicotreme(membrane opening). As a consequence, the amplitude maximum for each audible frequency is located at a specific point in the endolymphatic channel. Thus, the amplitude maximum for an oscillation frequency of 4000 per 1 s is at a distance of 10 mm from the oval foramen, and 1000 per 1 s is 23 mm. At the top (in helicotremy) there is an amplitude maximum for a frequency of 200 per 1 second.

The so-called spatial (principle of place) theory of encoding the height of the primal tone in the recipe itself is based on these phenomena.

Rice. 162. A- propagation of a sound wave by a curl; b frequency maximum depending on wavelength: AND- 700 Hz; 2 - 3,000 Hz

Tory. The amplitude maximum begins to appear at frequencies above 200 per 1 sec. The highest sensitivity of the human ear in the range of the human voice (from 1000 to 4000 Hz) is also reflected by the morphological features of the corresponding part of the helix: in the basal and middle helixes the highest density of afferent nerve endings is observed.

At the receptor level, the discrimination of sound information is just beginning; its final processing occurs in the nerve centers. In addition, in the frequency range of the human voice at the level of nerve centers there may be a summation of the excitation of several neurons, since each of them individually is not capable of reliably playing with its discharges sound frequencies above several hundred hertz.

Discrimination of sound intensity

More intense sounds are perceived by the human ear as louder. This process begins in the receptor itself, which structurally constitutes an integral organ. The main cells where RP curls originate are considered to be the inner hair cells. External cells probably increase this excitation slightly by transmitting their RP to internal ones.

Within the limits of the highest sensitivity for distinguishing sound intensity (1000-4000 Hz), a person hears a sound that has negligible energy (up to 1-12 erg1s * cm). At the same time, the sensitivity of the ear to sound vibrations in the second wave range is much lower, and within the range of audibility (closer to 20 or 20,000 Hz) the threshold sound energy should be no lower than 1 erg1s - cm2.

Too loud a sound may cause feeling of pain. The volume level when a person begins to feel pain is 130-140 dB above the threshold of audibility. If in your ear long time sound, especially loud sound, gradually develops the phenomenon of adaptation. A decrease in sensitivity is achieved primarily due to the contraction of the tension muscle and the stapes muscle, which change the intensity of the vibrations of the bones. In addition, many departments of auditory information processing, including receptor cells, are reached by efferent nerves, which can change their sensitivity and thereby participate in adaptation.

Central mechanisms for processing sound information

The fibers of the cochlear nerve (Fig. 163) reach the cochlear nuclei. After switching on the cells of the cochlear nuclei, APs arrive to the next cluster of nuclei: olivary complexes, lateral lemniscus. Next, the fibers are sent to the lower tubercles of the chotirigorbi body and the medial geniculate bodies - the main relay sections of the auditory system of the thalamus. Then they enter the thalamus, and only after the sound

Rice. 163. 1 - spiral organ; 2 - anterior core curls; 3 - posterior nucleus of the whorl; 4 - olive; 5 - additional core; 6 - side loop; 7 - lower tubercles of the chotirigorbicus plate; 8 - medial geniculate body; 9 - temporal cortex

the pathways enter the primary auditory cortex of the cerebral hemispheres, located in the temporal lobe. Next to it are located neurons belonging to the secondary auditory cortex.

The information contained in the sound stimulus, having passed through all the indicated switching nuclei, is repeatedly (at least 5 - 6 times) “registered” in the form of neural excitation. In this case, at each stage its corresponding analysis occurs, moreover, often with the connection of sensory signals from other, “non-auditory” parts of the central nervous system. As a result, reflex responses characteristic of the corresponding part of the central nervous system may arise. But recognition of sound, its meaningful awareness, occurs only if the impulses reach the cerebral cortex.

During the action of complex sounds that actually exist in nature, a peculiar mosaic of neurons appears in the nerve centers, which are excited simultaneously, and this mosaic map associated with the arrival of the corresponding sound is memorized.

Conscious assessment of the various properties of sound by a person is possible only with appropriate preliminary training. These processes occur most fully and efficiently only in cortical sections. Cortical neurons are activated differently: some are activated by the contralateral (opposite) ear, others by ipsilateral stimuli, and others only by simultaneous stimulation of both ears. They are usually excited whole sound groups. Damage to these parts of the central nervous system makes it difficult to perceive speech and spatial localization of the sound source.

Wide connections of the auditory areas of the central nervous system contribute to the interaction of sensory systems and formation of various reflexes. For example, when a sharp sound occurs, an unconscious turn of the head and eyes occurs towards its source and a redistribution of muscle tone (starting position).

Auditory orientation in space.

Quite accurate auditory orientation in space is possible only if binaural hearing. In this case, the fact that one ear is further from the sound source is of great importance. Considering that in the air, sound travels at a speed of 330 m1s, it travels 1 cm in 30 ms, and the slightest deviation of the sound source from the midline (even less than 3°) is already perceived by both ears with a time difference. That is, in this case, the separation factor both in time and in sound intensity matters. The ears, as horns, contribute to the concentration of sounds and also limit the flow of sound signals from the back of the head.

It is impossible to exclude the participation of the shape of the auricle in some individually determined change in sound modulations. In addition, the pinna and external auditory canal, having their own resonant frequency of about 3 kHz, enhance the sound intensity for tones similar to the range of the human voice.

Hearing acuity is measured using audiometer, is based on the arrival of pure tones of various frequencies through headphones and registration of the sensitivity threshold. Decreased sensitivity (deafness) may be associated with a violation of the state of the transmitting media (starting with the external auditory canal and eardrum) or hair cells and neural mechanisms of transmission and perception.

In the study of the physiology of hearing, the most important points are the questions of how sound vibrations reach the sensitive cells of the auditory apparatus and how the process of sound perception occurs.

The hearing organ provides transmission and perception of sound stimuli. As already mentioned, the entire hearing system is usually divided into a sound-conducting and sound-receiving part. The first includes the outer and middle ear, as well as the liquid media of the inner ear. The second part is represented by the nerve formations of the organ of Corti, auditory conductors and centers.

Sound waves, reaching the eardrum through the ear canal, set it in motion. The latter is designed in such a way that it resonates to certain air vibrations and has its own oscillation period (about 800 Hz).

The property of resonance is that the resonating body comes into forced vibration selectively at certain frequencies or even at one frequency.

When sound is transmitted through the ossicular system, the energy of sound vibrations increases. The lever system of the auditory ossicles, reducing the range of vibrations by 2 times, accordingly increases the pressure on the oval window. And since the eardrum is approximately 25 times larger than the surface of the oval window, the sound intensity when reaching the oval window is increased by 2x25 = 50 times. When transmitted from the oval window to the fluid of the labyrinth, the amplitude of vibrations decreases by 20 times, and the pressure of the sound wave increases by the same amount. The total increase in sound pressure in the middle ear system reaches 1000 times (2x25x20).

According to modern ideas, physiological significance muscles of the tympanic cavity is to improve the transmission of sound vibrations into the labyrinth. When the degree of tension of the muscles of the tympanic cavity changes, the degree of tension of the eardrum changes. Relaxing the eardrum improves the perception of rare vibrations, and increasing its tension improves the perception of frequent vibrations. By restructuring under the influence of sound stimulation, the muscles of the middle ear improve the perception of sounds of varying frequency and strength.

According to its action m. tensor tympani and m. stapedius are antagonists. With the contraction of m. tensor tympani the entire ossicular system is displaced inward and the stapes is pressed into the oval window. As a result, the pressure inside the labyrinth increases and the transmission of low and weak sounds deteriorates. Abbreviation m. stapedius produces reverse movement of the mobile formations of the middle ear. This limits the transmission of too strong and high sounds, but facilitates the transmission of low and weak ones.

It is believed that when exposed to very strong sounds, both muscles enter into tetanic contraction and thereby weaken the impact of powerful sounds.

Sound vibrations, passing through the middle ear system, cause the stapes plate to be pressed inward. Further, the vibrations are transmitted through the liquid media of the labyrinth to the organ of Corti. Here the mechanical energy of sound is converted into a physiological process.

IN anatomical structure organ of Corti, reminiscent of the structure of a piano, the entire main membrane throughout the 272 turns of the cochlea contains transverse striations due to a large number of connective tissue strands stretched in the form of strings. It is believed that such a detail of the organ of Corti provides stimulation of the receptors by sounds of different frequencies.

It has been suggested that vibrations of the main membrane on which the organ of Corti is located bring the hairs of the sensitive cells of the organ of Corti into contact with the integumentary membrane and during this contact auditory impulses arise, which are transmitted through conductors to the hearing centers, where the auditory sensation arises.

The process of converting the mechanical energy of sound into nervous energy associated with the excitation of receptor apparatus has not been studied. It was possible to determine the electrical component of this process in more or less detail. It has been established that under the action of an adequate stimulus, local electronegative potentials arise in the sensitive endings of receptor formations, which, having reached a certain strength, are transmitted through conductors to the auditory centers in the form of two-phase electric waves. Impulses entering the cerebral cortex cause excitation of nerve centers associated with electronegative potential. Although electrical phenomena do not reveal the fullness of the physiological processes of excitation, they still reveal some patterns of its development.

Kupffer gives the following explanation for the occurrence of electric current in the cochlea: as a result of sound stimulation, the superficially located colloidal particles of the labyrinthine fluid are charged with positive electricity, and negative electricity appears on the hair cells of the organ of Corti. This potential difference produces a current that is transmitted through the conductors.

According to V.F. Undritz, the mechanical energy of sound pressure in the organ of Corti is converted into electrical energy. Until now we have been talking about true action currents arising in the receptor apparatus and transmitted through the auditory nerve to the centers. Weaver and Bray discovered electrical potentials in the cochlea, which are a reflection of the mechanical vibrations occurring in it. As is known, the authors, by placing electrodes on the auditory nerve of a cat, observed electrical potentials corresponding to the frequency of the stimulated sound. At first it was suggested that the electrical phenomena they discovered were true nerve currents of action. Further analysis showed features of these potentials that are not characteristic of action currents. In the section on the physiology of hearing, it is necessary to mention the phenomena observed in the auditory analyzer during the action of stimuli, namely: adaptation, fatigue, sound masking.

As mentioned above, under the influence of stimuli, a restructuring of the function of the analyzers occurs. The latter is a protective reaction of the body when, with excessively intense sound stimulation or duration of stimulation, following the phenomenon of adaptation, fatigue sets in and a decrease in receptor sensitivity occurs; with mild stimulation, the phenomenon of sensitization occurs.

The adaptation time to sound depends on the frequency of the tone and the duration of its impact on the organ of hearing, ranging from 15 to 100 seconds.

Some researchers believe that the adaptation process is carried out due to processes occurring in the peripheral receptor apparatus. There are also indications of the role muscular apparatus the middle ear, thanks to which the hearing organ adapts to the perception of strong and weak sounds.

According to P.P. Lazarev, adaptation is a function of the organ of Corti. In the latter, under the influence of sound, the sound sensitivity of the substance decays. After the cessation of sound, sensitivity is restored due to another substance located in the supporting cells.

L. E. Commandants, based on personal experiences, came to the conclusion that the adaptation process is not determined by the strength of sound stimulation, but is regulated by processes occurring in the higher parts of the central nervous system.

G.V. Gershuni and G.V. Navyazhsky associate adaptive changes in the organ of hearing with changes in the activity of cortical centers. G.V. Navyazhsky believes that powerful sounds cause inhibition in the cerebral cortex, and suggests for preventive purposes For workers in noisy enterprises, perform “disinhibition” by exposure to low-frequency sounds.

Fatigue is a decrease in the performance of an organ that occurs as a result of prolonged work. It is expressed in a distortion of physiological processes, which is reversible. Sometimes, not functional, but organic changes occur and traumatic damage to the organ occurs due to an adequate irritant.

Masking of some sounds by others is observed during the simultaneous action of several different sounds on the organ of hearing; frequencies. The greatest masking effect in relation to any sound is possessed by sounds close in frequency to the overtones of the masking tone. Low tones have a great masking effect. The phenomena of masking are expressed by an increase in the threshold of audibility of the masked tone under the influence of the masking sound.

ROSZHELDOR

Siberian State University

communication routes.

Department: “Life Safety”.

Discipline: “Human Physiology”.

Course work.

Topic: “Physiology of hearing.”

Option number 9.

Completed by: student Reviewed by: associate professor

gr. BTP-311 Rublev M. G.

Ostashev V. A.

Novosibirsk 2006

Introduction.

Our world is filled with sounds, the most diverse.

we hear all this, all these sounds are perceived by our ear. In the ear the sound turns into “machine gun fire”

nerve impulses that are transmitted along the auditory nerve to the brain.

Sound, or sound wave, is alternating rarefaction and condensation of air, spreading in all directions from a vibrating body. We hear such air vibrations with a frequency of 20 to 20,000 per second.

20,000 vibrations per second is the highest sound of the smallest instrument in the orchestra - the piccolo flute, and 24 vibrations is the sound of the lowest string - the double bass.

The idea that sound “flies into one ear and out the other” is absurd. Both ears do the same job, but do not communicate with each other.

For example: the ringing of a clock “flew” into your ear. He faces an instant, but rather complex journey to the receptors, that is, to those cells in which a sound signal is born under the action of sound waves. Having flown into the ear, the ringing will hit the eardrum.

The membrane at the end of the auditory canal is stretched relatively tightly and closes the passage tightly. The ringing, striking the eardrum, causes it to vibrate and vibrate. The stronger the sound, the more the membrane vibrates.

The human ear is a unique hearing device in terms of sensitivity.

The goals and objectives of this course work are to familiarize a person with the sense organs - hearing.

Talk about the structure and functions of the ear, as well as how to preserve hearing and how to deal with diseases of the hearing organ.

Also about various harmful factors at work that can damage hearing, and about measures to protect against such factors, since various diseases of the hearing organ can lead to more serious consequences - hearing loss and illness of the entire human body.

I. The importance of knowledge of hearing physiology for safety engineers.

Physiology is a science that studies the functions of the whole organism, individual systems and sensory organs. One of the sense organs is hearing. A safety engineer is required to know the physiology of hearing, since at his enterprise, as part of his duty, he comes into contact with the professional selection of persons, determining their suitability for this or that type of work, for this or that profession.

Based on data on the structure and function of the upper respiratory tract and ear, the question is decided in what type of production a person can work in and in which not.

Let's look at examples of several specialties.

Good hearing is necessary for people to control the operation of clock mechanisms, when testing motors and various equipment. Also, good hearing is necessary for doctors and drivers of various types of transport - land, rail, air, water.

The work of signalmen completely depends on the state of the auditory function. Radiotelegraph operators servicing radio communication and hydroacoustics devices involved in listening to underwater sounds or noise detection.

In addition to hearing sensitivity, they must also have a high perception of tone frequency differences. Radiotelegraph operators must have rhythmic hearing and memory for rhythm. Good rhythmic sensitivity is considered to be the error-free discrimination of all signals or no more than three errors. Unsatisfactory – if less than half of the signals are distinguished.

During the professional selection of pilots, parachutists, sailors, and submariners, it is very important to determine the barofunction of the ear and paranasal sinuses.

Barofunction is the ability to respond to fluctuations in external pressure. And also have binaural hearing, that is, have spatial hearing and determine the position of the sound source in space. This property is based on the presence of two symmetrical halves of the auditory analyzer.

For fruitful and accident-free work, according to PTE and PTB, all persons in the above-mentioned specialties must undergo a medical commission to determine their ability to work in a given area, as well as for occupational safety and health.

II . Anatomy of the hearing organs.

The hearing organs are divided into three sections:

1. Outer ear. The external ear contains the external auditory canal and the pinna with muscles and ligaments.

2. Middle ear. The middle ear contains the eardrum, mastoid appendages and the auditory tube.

3. Inner ear. The inner ear contains the membranous labyrinth, which is located in the bony labyrinth inside the pyramid of the temporal bone.

Outer ear.

The auricle is an elastic cartilage of complex shape, covered with skin. Its concave surface faces forward, the lower part - the lobule of the auricle - the lobe, is devoid of cartilage and filled with fat. On the concave surface there is an antihelix, in front of it there is a depression - the concha of the ear, at the bottom of which there is an external auditory opening limited in front by the tragus. The external auditory canal consists of cartilaginous and bone sections.

The eardrum separates the outer ear from the middle ear. It is a plate consisting of two layers of fibers. The outer fibers are arranged radially, and the inner fibers are circular.

In the center of the eardrum there is a depression - the navel - the place where one of the auditory ossicles - the malleus - is attached to the eardrum. The tympanic membrane is inserted into the groove of the tympanic part of the temporal bone. The membrane is divided into an upper (smaller) free, unstretched part and a lower (larger) tense part. The membrane is located obliquely relative to the axis of the auditory canal.

Middle ear.

The tympanic cavity is air-filled, located at the base of the pyramid of the temporal bone, the mucous membrane is lined with single-layer squamous epithelium, which turns into cubic or cylindrical.

The cavity contains three auditory ossicles, tendons of the muscles that stretch the tympanic membrane and the stapes. The chorda tympani, a branch of the intermediate nerve, also passes here. The tympanic cavity passes into the auditory tube, which opens in the nasal part of the pharynx with the pharyngeal opening of the auditory tube.

The cavity has six walls:

1. The upper - tegmental wall separates the tympanic cavity from the cranial cavity.

2. The lower - jugular wall separates the tympanic cavity from the jugular vein.

3. Median - labyrinthine wall separates the tympanic cavity from the bony labyrinth of the inner ear. It has a window of the vestibule and a window of the cochlea, leading to the sections of the bony labyrinth. The window of the vestibule is closed by the base of the stapes, the window of the cochlea is closed by the secondary tympanic membrane. Above the window of the vestibule, the wall of the facial nerve protrudes into the cavity.

4. Literal - the membranous wall is formed by the tympanic membrane and the surrounding parts of the temporal bone.

5. The anterior - carotid wall separates the tympanic cavity from the canal of the internal carotid artery, and the tympanic opening of the auditory tube opens on it.

6. In the area of ​​the posterior mastoid wall there is an entrance to the mastoid cave; below it there is a pyramidal eminence, inside which the stapedius muscle begins.

The auditory ossicles are the stirrup, incus and malleus.

They are named so due to their shape - the smallest in the human body, they form a chain connecting the eardrum with the window of the vestibule leading to the inner ear. The ossicles transmit sound vibrations from the eardrum to the window of the vestibule. The handle of the hammer is fused to the eardrum. The head of the malleus and the body of the incus are connected to each other by a joint and strengthened by ligaments. The long process of the incus articulates with the head of the stapes, the base of which enters the window of the vestibule, connecting to its edge through the annular ligament of the stapes. The bones are covered with a mucous membrane.

The tendon of the tensor tympani muscle is attached to the handle of the malleus, and the stapedius muscle is attached to the stapes near its head. These muscles regulate the movement of the bones.

The auditory tube (Eustachian tube), about 3.5 cm long, performs a very important function - it helps to equalize the air pressure inside the tympanic cavity in relation to the external environment.

Inner ear.

The inner ear is located in the temporal bone. In the bone labyrinth, lined from the inside with periosteum, lies the membranous labyrinth, repeating the shape of the bone labyrinth. Between both labyrinths there is a gap filled with perilymph. The walls of the bone labyrinth are formed by compact bone tissue. It is located between the tympanic cavity and the internal auditory canal and consists of the vestibule, three semicircular canals and the cochlea.

The bony vestibule is an oval cavity communicating with the semicircular canals; on its wall there is a window of the vestibule, at the beginning of the cochlea there is a window of the cochlea.

The three bony semicircular canals lie in three mutually perpendicular planes. Each semicircular canal has two legs, one of which expands before entering the vestibule, forming an ampulla. The adjacent pedicles of the anterior and posterior canals are connected to form a common bony pedicle, so the three canals open into the vestibule with five openings. The bony cochlea forms 2.5 turns around a horizontally lying rod - a spindle, around which a bone spiral plate is twisted like a screw, pierced by thin canaliculi, where the fibers of the cochlear part of the vestibulocochlear nerve pass. At the base of the plate there is a spiral canal in which lies the spiral node - the organ of Corti. It consists of many fibers stretched like strings.

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Sound is vibrations, i.e. periodic mechanical disturbance in elastic media - gaseous, liquid and solid. Such a disturbance, which represents some physical change in the medium (for example, a change in density or pressure, displacement of particles), propagates in it in the form of a sound wave. A sound may be inaudible if its frequency is beyond the sensitivity of the human ear, or if it travels through a medium, such as a solid, that cannot have direct contact with the ear, or if its energy is rapidly dissipated in the medium. Thus, the process of perceiving sound that is usual for us is only one side of acoustics.

Sound waves

Sound wave

Sound waves can serve as an example of an oscillatory process. Any oscillation is associated with a violation of the equilibrium state of the system and is expressed in the deviation of its characteristics from equilibrium values ​​with a subsequent return to the original value. For sound vibrations, this characteristic is the pressure at a point in the medium, and its deviation is the sound pressure.

Consider a long pipe filled with air. A piston that fits tightly to the walls is inserted into it at the left end. If the piston is sharply moved to the right and stopped, the air in the immediate vicinity of it will be compressed for a moment. The compressed air will then expand, pushing the air adjacent to it to the right, and the area of ​​compression initially created near the piston will move through the pipe at a constant speed. This compression wave is the sound wave in the gas.
That is, a sharp displacement of particles of an elastic medium in one place will increase the pressure in this place. Thanks to the elastic bonds of particles, pressure is transmitted to neighboring particles, which, in turn, affect the next ones, and the area of ​​​​increased pressure seems to move in an elastic medium. A region of high pressure is followed by a region of low pressure, and thus a series of alternating regions of compression and rarefaction are formed, propagating in the medium in the form of a wave. Each particle of the elastic medium in this case will perform oscillatory movements.

A sound wave in a gas is characterized by excess pressure, excess density, displacement of particles and their speed. For sound waves, these deviations from equilibrium values ​​are always small. Thus, the excess pressure associated with the wave is much less than the static pressure of the gas. Otherwise, we are dealing with another phenomenon - a shock wave. In a sound wave corresponding to normal speech, the excess pressure is only about one millionth of atmospheric pressure.

The important fact is that the substance is not carried away by the sound wave. A wave is only a temporary disturbance passing through the air, after which the air returns to an equilibrium state.
Wave motion, of course, is not unique to sound: light and radio signals travel in the form of waves, and everyone is familiar with waves on the surface of water.

So the sound is in a broad sense- elastic waves propagating in any elastic medium and creating mechanical vibrations in it; in a narrow sense, the subjective perception of these vibrations by the special sense organs of animals or humans.
Like any wave, sound is characterized by amplitude and frequency spectrum. Typically, a person hears sounds transmitted through the air in the frequency range from 16-20 Hz to 15-20 kHz. Sound below the range of human audibility is called infrasound; higher: up to 1 GHz, - ultrasound, from 1 GHz - hypersound. Among the audible sounds, one should also highlight phonetic, speech sounds and phonemes (which make up oral speech) and musical sounds (which make up music).

Longitudinal and transverse sound waves are distinguished depending on the ratio of the direction of propagation of the wave and the direction of mechanical vibrations of the particles of the propagation medium.
In liquid and gaseous media, where there are no significant fluctuations in density, acoustic waves are longitudinal in nature, that is, the direction of vibration of the particles coincides with the direction of movement of the wave. IN solids, in addition to longitudinal deformations, elastic shear deformations also occur, causing the excitation of transverse (shear) waves; in this case, the particles oscillate perpendicular to the direction of wave propagation. The speed of propagation of longitudinal waves is much greater than the speed of propagation of shear waves.

The air is not uniform for sound everywhere. It is known that air is constantly in motion. The speed of its movement in different layers is not the same. In layers close to the ground, the air comes into contact with its surface, buildings, forests, and therefore its speed here is less than at the top. Due to this, the sound wave does not travel equally fast at the top and bottom. If the movement of air, i.e., the wind, is a companion to sound, then in the upper layers of the air the wind will drive the sound wave more strongly than in the lower layers. When there is a headwind, sound at the top travels slower than at the bottom. This difference in speed affects the shape of the sound wave. As a result of wave distortion, sound does not travel straight. With a tailwind, the line of propagation of the sound wave bends downward, and with a headwind, it bends upward.

Another reason for the uneven propagation of sound in the air. This - different temperature its individual layers.

Unevenly heated layers of air, like the wind, change the direction of sound. During the day, the sound wave bends upward because the speed of sound in the lower, hotter layers is greater than in the upper layers. In the evening, when the earth, and with it the nearby layers of air, quickly cool, the upper layers become warmer than the lower ones, the speed of sound in them is greater, and the line of propagation of sound waves bends downward. Therefore, in the evenings, out of the blue, you can hear better.

Watching clouds, you can often notice how at different heights they move not only at different speeds, but sometimes at different speeds. different directions. This means that the wind at different heights from the ground may have different speeds and directions. The shape of the sound wave in such layers will also change from layer to layer. Let, for example, the sound come against the wind. In this case, the sound propagation line should bend and go upward. But if a layer of slow-moving air gets in its way, it will change its direction again and may return to the ground again. It is then that in the space from the place where the wave rises in height to the place where it returns to the ground, a “zone of silence” appears.

Organs of sound perception

Hearing - ability biological organisms perceive sounds with the hearing organs; a special function of the hearing aid excited by sound vibrations environment, for example air or water. One of the biological five senses, also called acoustic perception.

The human ear perceives sound waves with a length of approximately 20 m to 1.6 cm, which corresponds to 16 - 20,000 Hz (oscillations per second) when vibrations are transmitted through the air, and up to 220 kHz when sound is transmitted through the bones of the skull. These waves have important biological significance, for example, sound waves in the range of 300-4000 Hz correspond to the human voice. Sounds above 20,000 Hz are of little practical importance as they decelerate quickly; vibrations below 60 Hz are perceived through the vibration sense. The range of frequencies that a person is able to hear is called the auditory or sound range; higher frequencies are called ultrasound, and lower frequencies are called infrasound.
The ability to distinguish sound frequencies greatly depends on the individual: his age, gender, susceptibility to hearing diseases, training and hearing fatigue. Individuals are capable of perceiving sound up to 22 kHz, and possibly higher.
A person can distinguish several sounds at the same time due to the fact that there can be several standing waves in the cochlea at the same time.

The ear is a complex vestibular-auditory organ that performs two functions: it perceives sound impulses and is responsible for the position of the body in space and the ability to maintain balance. This is a paired organ that is located in the temporal bones of the skull, limited externally by the auricles.

The organ of hearing and balance is represented by three sections: the outer, middle and inner ear, each of which performs its own specific functions.

The outer ear consists of the pinna and the external auditory canal. The auricle is a complex-shaped elastic cartilage covered with skin; its lower part, called the lobe, is a skin fold that consists of skin and adipose tissue.
The auricle in living organisms works as a receiver of sound waves, which are then transmitted to inner part hearing aid. The value of the auricle in humans is much smaller than in animals, so in humans it is practically motionless. But many animals, by moving their ears, are able to determine the location of the source of sound much more accurately than humans.

The folds of the human auricle introduce small frequency distortions into the sound entering the ear canal, depending on the horizontal and vertical localization of the sound. Thus, the brain receives additional information to clarify the location of the sound source. This effect is sometimes used in acoustics, including to create the sensation of surround sound when using headphones or hearing aids.
The function of the auricle is to catch sounds; its continuation is the cartilage of the external auditory canal, the length of which is on average 25-30 mm. The cartilaginous part of the auditory canal passes into the bone, and the entire external auditory canal is lined with skin containing sebaceous and sulfur glands, which are modified sweat glands. This passage ends blindly: it is separated from the middle ear by the eardrum. Sound waves captured by the auricle hit the eardrum and cause it to vibrate.

In turn, vibrations from the eardrum are transmitted to the middle ear.

Middle ear
The main part of the middle ear is the tympanic cavity - a small space with a volume of about 1 cm³ located in the temporal bone. There are three auditory bones here: the malleus, the incus and the stirrup - they transmit sound vibrations from the outer ear to the inner ear, simultaneously amplifying them.

The auditory ossicles, as the smallest fragments of the human skeleton, represent a chain that transmits vibrations. The handle of the malleus is closely fused with the eardrum, the head of the malleus is connected to the incus, and that, in turn, with its long process, is connected to the stapes. The base of the stapes closes the window of the vestibule, thus connecting to the inner ear.
The middle ear cavity is connected to the nasopharynx through the Eustachian tube, through which the average air pressure inside and outside the eardrum is equalized. When external pressure changes, the ears sometimes become blocked, which is usually resolved by yawning reflexively. Experience shows that ear congestion is solved even more effectively by swallowing movements or by blowing into a pinched nose at this moment.

Inner ear
Of the three sections of the organ of hearing and balance, the most complex is the inner ear, which, due to its intricate shape, is called the labyrinth. The bony labyrinth consists of the vestibule, cochlea and semicircular canals, but only the cochlea, filled with lymphatic fluids, is directly related to hearing. Inside the cochlea there is a membranous canal, also filled with liquid, on the lower wall of which there is a receptor apparatus of the auditory analyzer, covered with hair cells. Hair cells detect vibrations of the fluid filling the canal. Each hair cell is tuned to a specific sound frequency, with cells tuned to low frequencies located at the top of the cochlea, and high frequencies tuned to cells at the bottom of the cochlea. When hair cells die from age or for other reasons, a person loses the ability to perceive sounds of the corresponding frequencies.

Limits of Perception

The human ear nominally hears sounds in the range of 16 to 20,000 Hz. The upper limit tends to decrease with age. Most adults cannot hear sounds above 16 kHz. The ear itself does not respond to frequencies below 20 Hz, but they can be sensed through the sense of touch.

The range of loudness of perceived sounds is enormous. But the eardrum in the ear is only sensitive to changes in pressure. Sound pressure level is usually measured in decibels (dB). The lower threshold of audibility is defined as 0 dB (20 micropascals), and the definition of the upper limit of audibility refers rather to the threshold of discomfort and then to hearing impairment, contusion, etc. This limit depends on how long we listen to the sound. The ear can tolerate short-term increases in volume up to 120 dB without consequences, but long-term exposure to sounds above 80 dB can cause hearing loss.

More careful studies of the lower limit of hearing have shown that the minimum threshold at which sound remains audible depends on frequency. This graph is called the absolute hearing threshold. On average, it has a region of greatest sensitivity in the range from 1 kHz to 5 kHz, although sensitivity decreases with age in the range above 2 kHz.
There is also a way to perceive sound without the participation of the eardrum - the so-called microwave auditory effect, when modulated radiation in the microwave range (from 1 to 300 GHz) affects the tissue around the cochlea, causing a person to perceive various sounds.
Sometimes a person can hear sounds in the low-frequency region, although in reality there were no sounds of this frequency. This happens because the vibrations of the basilar membrane in the ear are not linear and vibrations can occur in it with a difference frequency between two higher frequencies.

Synesthesia

One of the most unusual psychoneurological phenomena, in which the type of stimulus and the type of sensations that a person experiences do not coincide. Synaesthetic perception is expressed in the fact that in addition to ordinary qualities, additional, simpler sensations or persistent “elementary” impressions may arise - for example, color, smell, sounds, tastes, qualities of a textured surface, transparency, volume and shape, location in space and other qualities , not received through the senses, but existing only in the form of reactions. Such additional qualities may either arise as isolated sensory impressions or even manifest physically.

There is, for example, auditory synesthesia. This is the ability of some people to "hear" sounds when observing moving objects or flashes, even if they are not accompanied by actual sound phenomena.
It should be borne in mind that synesthesia is rather a psychoneurological feature of a person and is not a mental disorder. This perception of the surrounding world can be felt a common person through the use of certain drugs.

There is no general theory of synesthesia (a scientifically proven, universal idea about it) yet. Currently, there are many hypotheses and a lot of research is being conducted in this area. Original classifications and comparisons have already appeared, and certain strict patterns have emerged. For example, we scientists have already found out that synesthetes have a special nature of attention - as if “preconscious” - to those phenomena that cause synesthesia in them. Synesthetes have a slightly different brain anatomy and a radically different activation of the brain to synaesthetic “stimuli.” And researchers from the University of Oxford (UK) conducted a series of experiments during which they found that the cause of synesthesia may be overexcitable neurons. The only thing that can be said for sure is that such perception is obtained at the level of brain function, and not at the level of primary perception of information.

Conclusion

Pressure waves travel through the outer ear, eardrum, and middle ear ossicles to reach the fluid-filled, cochlear-shaped inner ear. The liquid, oscillating, hits a membrane covered with tiny hairs, cilia. The sinusoidal components of a complex sound cause vibrations in various parts of the membrane. The cilia vibrating together with the membrane excite the nerve fibers associated with them; a series of pulses appear in them, in which the frequency and amplitude of each component of a complex wave are “encoded”; this data is electrochemically transmitted to the brain.

Of the entire spectrum of sounds, the audible range is primarily distinguished: from 20 to 20,000 hertz, infrasound (up to 20 hertz) and ultrasound - from 20,000 hertz and above. A person cannot hear infrasounds and ultrasounds, but this does not mean that they do not affect him. It is known that infrasounds, especially below 10 hertz, can influence the human psyche and cause depressive states. Ultrasounds can cause astheno-vegetative syndromes, etc.
The audible part of the sound range is divided into low-frequency sounds - up to 500 hertz, mid-frequency - 500-10,000 hertz and high-frequency - over 10,000 hertz.

This division is very important, since the human ear is not equally sensitive to different sounds. The ear is most sensitive to a relatively narrow range of mid-frequency sounds from 1000 to 5000 hertz. To lower and higher frequency sounds, sensitivity drops sharply. This leads to the fact that a person is able to hear sounds with an energy of about 0 decibels in the mid-frequency range and not hear low-frequency sounds of 20-40-60 decibels. That is, sounds with the same energy in the mid-frequency range can be perceived as loud, but in the low-frequency range as quiet or not be heard at all.

This feature of sound was not formed by nature by chance. The sounds necessary for its existence: speech, sounds of nature, are mainly in the mid-frequency range.
The perception of sounds is significantly impaired if other sounds, noises similar in frequency or harmonic composition, are heard at the same time. This means, on the one hand, the human ear does not perceive low-frequency sounds well, and, on the other hand, if there is extraneous noise in the room, then the perception of such sounds can be further disrupted and distorted.

Consists of the outer, middle and inner ear. The middle and inner ear are located inside the temporal bone.

Outer ear consists of the auricle (collects sounds) and the external auditory canal, which ends in the eardrum.

Middle ear- This is a chamber filled with air. It contains the auditory ossicles (hammer, incus and stapes), which transmit vibrations from the eardrum to the membrane of the oval window - they amplify the vibrations 50 times. The middle ear is connected to the nasopharynx via the Eustachian tube, through which the pressure in the middle ear is equalized with atmospheric pressure.

In the inner ear there is a cochlea - a fluid-filled bone canal twisted in 2.5 turns, blocked by a longitudinal septum. On the septum there is an organ of Corti containing hair cells - these are auditory receptors that convert sound vibrations into nerve impulses.

Ear work: When the stapes presses on the membrane of the oval window, the column of fluid in the cochlea moves, and the membrane of the round window protrudes into the middle ear. The movement of the fluid causes the hairs to touch the integumentary plate, causing the hair cells to become excited.

Vestibular apparatus: in the inner ear, in addition to the cochlea, there are semicircular canals and vestibular sacs. Hair cells in the semicircular canals sense fluid movement and respond to acceleration; hair cells in the sacs sense the movement of the otolith pebble attached to them and determine the position of the head in space.

Establish a correspondence between the structures of the ear and the sections in which they are located: 1) outer ear, 2) middle ear, 3) inner ear. Write the numbers 1, 2 and 3 in the correct order.
A) auricle
B) oval window
B) snail
D) stirrup
D) Eustachian tube
E) hammer

Establish a correspondence between the function of the hearing organ and the section that performs this function: 1) middle ear, 2) inner ear
A) conversion of sound vibrations into electrical ones
B) amplification of sound waves due to vibrations of the auditory ossicles
B) equalization of pressure on the eardrum
D) conducting sound vibrations due to the movement of liquid
D) irritation of auditory receptors

1. Establish the sequence of sound wave transmission to the auditory receptors. Write down the corresponding sequence of numbers.
1) vibrations of the auditory ossicles
2) vibrations of fluid in the cochlea
3) vibrations of the eardrum
4) irritation of auditory receptors

2. Establish the correct sequence of passage of a sound wave in the human hearing organ. Write down the corresponding sequence of numbers.
1) eardrum
2) oval window
3) stirrup
4) anvil
5) hammer
6) hair cells

3. Establish the sequence in which sound vibrations are transmitted to the receptors of the hearing organ. Write down the corresponding sequence of numbers.
1) Outer ear
2) Membrane of the oval window
3) Auditory ossicles
4) Eardrum
5) Fluid in the cochlea
6) Hearing receptors

1. Select three correctly labeled captions for the drawing “Structure of the Ear.”
1) external auditory canal
2) eardrum
3) auditory nerve
4) stirrup
5) semicircular canal
6) snail

2. Select three correctly labeled captions for the drawing “Structure of the Ear.” Write down the numbers under which they are indicated.
1) ear canal
2) eardrum
3) auditory ossicles
4) auditory tube
5) semicircular canals
6) auditory nerve

4. Select three correctly labeled captions for the drawing “Structure of the Ear.”
1) auditory ossicles
2) facial nerve
3) eardrum
4) auricle
5) middle ear
6) vestibular apparatus

1. Set the sequence of sound transmission in the hearing analyzer. Write down the corresponding sequence of numbers.
1) vibration of the auditory ossicles
2) fluid vibrations in the cochlea
3) generation of a nerve impulse

5) transmission of nerve impulses along the auditory nerve to the temporal lobe of the cerebral cortex
6) vibration of the oval window membrane
7) vibration of hair cells

2. Establish the sequence of processes occurring in the auditory analyzer. Write down the corresponding sequence of numbers.
1) transmission of vibrations to the membrane of the oval window
2) capturing the sound wave
3) irritation of receptor cells with hairs
4) vibration of the eardrum
5) movement of fluid in the cochlea
6) vibration of the auditory ossicles
7) the occurrence of a nerve impulse and its transmission along the auditory nerve to the brain

3. Establish the sequence of processes of passage of a sound wave in the organ of hearing and a nerve impulse in the auditory analyzer. Write down the corresponding sequence of numbers.
1) movement of fluid in the cochlea
2) transmission of sound waves through the malleus, incus and stapes
3) transmission of nerve impulses along the auditory nerve
4) vibration of the eardrum
5) conduction of sound waves through the external auditory canal

4. Establish the path of the sound wave of a car siren that a person will hear, and the nerve impulse that occurs when it sounds. Write down the corresponding sequence of numbers.
1) snail receptors
2) auditory nerve
3) auditory ossicles
4) eardrum
5) auditory cortex

Choose the one that suits you best correct option. The auditory analyzer receptors are located
1) in the inner ear
2) in the middle ear
3) on the eardrum
4) in the auricle

Choose one, the most correct option. The sound signal is converted into nerve impulses in
1) snail
2) semicircular canals
3) eardrum
4) auditory ossicles

Choose one, the most correct option. In the human body, an infection from the nasopharynx enters the middle ear cavity through
1) oval window
2) larynx
3) auditory tube
4) inner ear

Establish a correspondence between the parts of the human ear and their structure: 1) outer ear, 2) middle ear, 3) inner ear. Write the numbers 1, 2, 3 in the order corresponding to the letters.
A) includes the auricle and external auditory canal
B) includes the cochlea, which contains the initial section of the sound-receiving apparatus
B) includes three auditory ossicles
D) includes the vestibule with three semicircular canals, in which the balance apparatus is located
D) a cavity filled with air communicates through the auditory tube with the pharyngeal cavity
E) the inner end is covered by the eardrum

1. Establish a correspondence between structures and analyzers: 1) Visual, 2) Auditory. Write numbers 1 and 2 in the correct order.
A) Snail
B) Anvil
B) Vitreous body
D) Sticks
D) Cones
E) Eustachian tube

2. Establish a correspondence between the characteristics and analyzers of a person: 1) visual, 2) auditory. Write numbers 1 and 2 in the order corresponding to the letters.
A) perceives mechanical vibrations of the environment
B) includes rods and cones
B) the central section is located in the temporal lobe of the cerebral cortex
D) the central department is located in occipital lobe cerebral cortex
D) includes the organ of Corti

Select three correctly labeled captions for the figure “Structure of the vestibular apparatus.” Write down the numbers under which they are indicated.
1) Eustachian tube
2) snail
3) calcareous crystals
4) hair cells
5) nerve fibers
6) inner ear

Choose one, the most correct option. Pressure on the eardrum equal to atmospheric pressure from the middle ear is provided in humans
1) auditory tube
2) auricle
3) membrane of the oval window
4) auditory ossicles

Choose one, the most correct option. Receptors that determine the position of the human body in space are located in
1) membrane of the oval window
2) eustachian tube
3) semicircular canals
4) middle ear

Choose three correct answers out of six and write down the numbers under which they are indicated. The hearing analyzer includes:
1) auditory ossicles
2) receptor cells
3) auditory tube
4) auditory nerve
5) semicircular canals
6) temporal lobe cortex

Choose three correct answers out of six and write down the numbers under which they are indicated. The middle ear in the human hearing organ includes
1) receptor apparatus
2) anvil
3) auditory tube
4) semicircular canals
5) hammer
6) auricle

Choose three correct answers out of six and write down the numbers under which they are indicated. What should be considered true signs of the human hearing organ?
1) The external auditory canal is connected to the nasopharynx.
2) Sensitive hair cells are located on the membrane of the cochlea of ​​the inner ear.
3) The middle ear cavity is filled with air.
4) The middle ear is located in the labyrinth of the frontal bone.
5) The outer ear detects sound vibrations.
6) The membranous labyrinth amplifies sound vibrations.

© D.V. Pozdnyakov, 2009-2019

For our orientation in the world around us, hearing plays the same role as vision. The ear allows us to communicate with each other using sounds; it has a special sensitivity to the sound frequencies of speech. With the help of the ear, a person picks up various sound vibrations in the air. Vibrations that come from an object (sound source) are transmitted through the air, which plays the role of a sound transmitter, and are captured by the ear. The human ear perceives air vibrations with a frequency of 16 to 20,000 Hz. Vibrations with a higher frequency are considered ultrasonic, but the human ear does not perceive them. The ability to distinguish high tones decreases with age. The ability to pick up sound with both ears makes it possible to determine where it is. In the ear, air vibrations are converted into electrical impulses, which are perceived by the brain as sound.

The ear also houses the organ for sensing movement and position of the body in space - vestibular apparatus. The vestibular system plays a large role in a person’s spatial orientation, analyzes and transmits information about accelerations and decelerations of linear and rotational movement, as well as when the position of the head changes in space.

Ear structure

Based external structure the ear is divided into three parts. The first two parts of the ear, the external (outer) and middle, conduct sound. The third part - the inner ear - contains auditory cells, mechanisms for perceiving all three features of sound: pitch, strength and timbre.

Outer ear- the protruding part of the outer ear is called auricle, its basis is made up of semi-rigid supporting tissue - cartilage. The anterior surface of the auricle has a complex structure and variable shape. It consists of cartilage and fibrous tissue, with the exception of the lower part - lobules ( earlobe) formed by fatty tissue. At the base of the auricle there are anterior, superior and posterior auricular muscles, the movements of which are limited.

In addition to the acoustic (sound-collecting) function, the auricle plays a protective role, protecting the auditory canal into the eardrum from harmful effects environment (ingress of water, dust, strong air currents). Both the shape and size of the ears are individual. The length of the auricle in men is 50–82 mm and the width is 32–52 mm; in women the sizes are slightly smaller. The small area of ​​the auricle represents all the sensitivity of the body and internal organs. Therefore, it can be used to obtain biologically important information about the state of any organ. The auricle concentrates sound vibrations and directs them to the external auditory opening.

External auditory canal serves to conduct sound vibrations of air from the auricle to the eardrum. The external auditory canal has a length of 2 to 5 cm. Its outer third is formed by cartilage tissue, and the inner 2/3 is formed by bone. The external auditory canal is arched in the superior-posterior direction, and easily straightens when the auricle is pulled up and back. In the skin of the ear canal there are special glands that secrete a yellowish secretion ( earwax), the function of which is to protect the skin from bacterial infection and foreign particles (insects).

The external auditory canal is separated from the middle ear by the eardrum, which is always retracted inward. This is a thin connective tissue plate covered on the outside stratified epithelium, and from the inside - the mucous membrane. The external auditory canal serves to conduct sound vibrations to the eardrum, which separates the outer ear from the tympanic cavity (middle ear).

Middle ear, or the tympanic cavity, is a small air-filled chamber that is located in the pyramid of the temporal bone and is separated from the external auditory canal by the eardrum. This cavity has bony and membranous (tympanic membrane) walls.

Eardrum is a low-moving membrane with a thickness of 0.1 microns, woven from fibers that go in different directions and are unevenly stretched in different areas. Due to this structure, the eardrum does not have its own period of oscillation, which would lead to amplification of sound signals that coincide with the frequency of its own oscillations. It begins to vibrate under the influence of sound vibrations passing through the external auditory canal. Through the hole on back wall The tympanic membrane communicates with the mastoid cave.

The opening of the auditory (Eustachian) tube is located in the anterior wall of the tympanic cavity and leads to the nasal part of the pharynx. Thanks to this, atmospheric air can enter the tympanic cavity. Normally, the opening of the Eustachian tube is closed. It opens during swallowing movements or yawning, helping to equalize the air pressure on the eardrum from the side of the middle ear cavity and the external auditory opening, thereby protecting it from ruptures leading to hearing impairment.

In the tympanic cavity lie auditory ossicles. They are very small in size and are connected in a chain that extends from the eardrum to inner wall tympanic cavity.

The outermost bone is hammer- its handle is connected to the eardrum. The head of the malleus is connected to the incus, which movably articulates with the head stirrups.

The auditory ossicles received such names because of their shape. The bones are covered with a mucous membrane. Two muscles regulate the movement of the bones. The connection of the bones is such that it increases the pressure of sound waves on the membrane of the oval window by 22 times, which allows weak sound waves to move the liquid in snail.

Inner ear enclosed in the temporal bone and is a system of cavities and canals located in the bone substance of the petrous part of the temporal bone. Together they form the bony labyrinth, within which is the membranous labyrinth. Bone labyrinth represents bone cavities various shapes and consists of the vestibule, three semicircular canals and the cochlea. Membranous labyrinth consists of a complex system of thin membranous formations located in the bony labyrinth.

All cavities of the inner ear are filled with fluid. Inside the membranous labyrinth there is endolymph, and the fluid washing the membranous labyrinth outside is perilymph and is similar in composition to cerebrospinal fluid. Endolymph differs from perilymph (it contains more potassium ions and fewer sodium ions) - it carries a positive charge in relation to perilymph.

Prelude- the central part of the bony labyrinth, which communicates with all its parts. Posterior to the vestibule are three bony semicircular canals: superior, posterior and lateral. The lateral semicircular canal lies horizontally, the other two are at right angles to it. Each channel has an expanded part - an ampoule. It contains a membranous ampulla filled with endolymph. When the endolymph moves during a change in the position of the head in space, the nerve endings are irritated. Excitation is transmitted along nerve fibers to the brain.

Snail is a spiral tube that forms two and a half turns around a cone-shaped bone rod. It is the central part of the hearing organ. Inside the bony canal of the cochlea there is a membranous labyrinth, or cochlear duct, to which the endings of the cochlear part of the eighth cranial nerve Perilymph vibrations are transmitted to the endolymph of the cochlear duct and activate the nerve endings of the auditory part of the eighth cranial nerve.

The vestibulocochlear nerve consists of two parts. The vestibular part conducts nerve impulses from the vestibule and semicircular canals to the vestibular nuclei of the pons and medulla oblongata and further to the cerebellum. The cochlear part transmits information along fibers that follow from the spiral (corti) organ to the auditory nuclei of the brainstem and then - through a series of switchings in the subcortical centers - to the cortex of the upper part of the temporal lobe of the cerebral hemisphere.

Mechanism of perception of sound vibrations

Sounds arise due to air vibrations and are amplified in the auricle. The sound wave is then conducted through the external auditory canal to the eardrum, causing it to vibrate. The vibration of the eardrum is transmitted to the chain of auditory ossicles: the malleus, incus and stapes. The base of the stapes is fixed to the window of the vestibule with the help of an elastic ligament, due to which vibrations are transmitted to the perilymph. In turn, through the membranous wall of the cochlear duct, these vibrations pass to the endolymph, the movement of which causes irritation of the receptor cells of the spiral organ. The resulting nerve impulse follows the fibers of the cochlear part of the vestibulocochlear nerve to the brain.

The translation of sounds perceived by the organ of hearing as pleasant and unpleasant sensations is carried out in the brain. Irregular sound waves produce the sensation of noise, while regular, rhythmic waves are perceived as musical tones. Sounds travel at a speed of 343 km/s at an air temperature of 15–16ºС.

A sound wave is a double oscillation of the medium, in which a phase of increasing and decreasing pressure is distinguished. Sound vibrations enter the external auditory canal, reach the eardrum and cause it to vibrate. In the phase of increasing pressure or thickening, the eardrum, together with the handle of the hammer, moves inward. In this case, the body of the anvil, connected to the head of the hammer, is displaced outward, thanks to the suspensory ligaments, and the long sprout of the anvil is shifted inward, thus displacing the stirrup inward. By pressing into the window of the vestibule, the stapes jerkily leads to a displacement of the perilymph of the vestibule. Further propagation of the wave along the staircase of the vestibule transmits oscillatory movements to the Reissner membrane, which in turn sets in motion the endolymph and, through the main membrane, the perilymph of the scala tympani. As a result of this movement of the perilymph, vibrations of the main and Reissner membranes occur. With each movement of the stapes towards the vestibule, the perilymph ultimately leads to a displacement of the membrane of the vestibule towards the tympanic cavity. In the pressure reduction phase, the transmission system returns to its original position.

The air route for delivering sounds to the inner ear is the main one. Another way of conducting sounds to the spiral organ is bone (tissue) conduction. In this case, a mechanism comes into play in which sound vibrations of the air hit the bones of the skull, spread into them and reach the cochlea. However, the mechanism of bone-tissue sound transmission can be twofold. In one case, a sound wave in the form of two phases, propagating along the bone to the liquid media of the inner ear, in the pressure phase will protrude the membrane of the round window and, to a lesser extent, the base of the stapes (taking into account the practical incompressibility of the liquid). Simultaneously with such a compression mechanism, another - inertial option - can be observed. In this case, when sound is conducted through the bone, the vibration of the sound-conducting system will not coincide with the vibration of the skull bones and, therefore, the main and Reissner membranes will vibrate and excite the spiral organ in the usual way. Vibration of the skull bones can be caused by touching it with a sounding tuning fork or telephone. Thus, the bone transmission route becomes of great importance when sound transmission through air is disrupted.

Auricle. The role of the auricle in the physiology of human hearing is small. It has some significance in ototopics and as collectors of sound waves.

External auditory canal. It is shaped like a tube, making it a good conductor of sounds in depth. The width and shape of the ear canal does not play a special role in sound transmission. At the same time, its mechanical blockage prevents the propagation of sound waves to the eardrum and leads to a noticeable deterioration in hearing. In the auditory canal near the eardrum, a constant level of temperature and humidity is maintained, regardless of fluctuations in temperature and humidity in the external environment, which ensures the stability of the elastic media of the tympanic cavity. Due to the special structure of the outer ear, the pressure of the sound wave in the external auditory canal is twice as high as in the free sound field.

Eardrum and auditory ossicles. The main role of the eardrum and auditory ossicles is to transform sound vibrations of large amplitude and low force into vibrations of the fluids of the inner ear with low amplitude and high force (pressure). Vibrations of the eardrum bring the hammer, incus and stirrup into subordination. In turn, the stirrup transmits vibrations to the perilymph, which causes a displacement of the membranes of the cochlear duct. The movement of the main membrane causes irritation of the sensitive hair cells of the spiral organ, as a result of which nerve impulses arise that follow auditory pathway into the cerebral cortex.

The eardrum vibrates mainly in its lower quadrant with the synchronous movement of the hammer attached to it. Closer to the periphery, its fluctuations decrease. At maximum sound intensity, vibrations of the eardrum can vary from 0.05 to 0.5 mm, with the range of vibrations being larger for low-frequency tones and smaller for high-frequency tones.

The transformation effect is achieved due to the difference in the area of ​​the eardrum and the area of ​​the base of the stapes, the ratio of which is approximately 55:3 (area ratio 18:1), as well as due to the lever system of the auditory ossicles. When converted to dB, the lever action of the auditory ossicular system is 2 dB, and the increase in sound pressure due to the difference in the ratio of the effective areas of the eardrum to the base of the stapes provides a sound amplification of 23 - 24 dB.

According to Bekeshi /I960/, the total acoustic gain of the sound pressure transformer is 25 - 26 dB. This increase in pressure compensates for the natural loss of sound energy that occurs as a result of the reflection of a sound wave during its transition from air to liquid, especially for low and medium frequencies (Wulstein JL, 1972).

In addition to the transformation of sound pressure, the eardrum; also performs the function of sound protection (screening) of the snail window. Normally, sound pressure transmitted through the system of auditory ossicles to the media of the cochlea reaches the window of the vestibule somewhat earlier than it reaches the window of the cochlea through the air. Due to the pressure difference and phase shift, perilymph movement occurs, causing bending of the main membrane and irritation of the receptor apparatus. In this case, the membrane of the cochlear window oscillates synchronously with the base of the stapes, but in the opposite direction. In the absence of the eardrum, this mechanism of sound transmission is disrupted: the next sound wave from the external auditory canal simultaneously in phase reaches the window of the vestibule and the cochlea, as a result of which the effect of the wave cancels out each other. Theoretically, there should be no shift of the perilymph and irritation of the sensitive hair cells. In fact, with a complete defect of the eardrum, when both windows are equally accessible to sound waves, hearing is reduced to 45 - 50. Destruction of the chain of auditory ossicles is accompanied by significant hearing loss (up to 50-60 dB).

The design features of the lever system allow not only to amplify weak sounds, but also to perform a protective function to a certain extent - to weaken the transmission of strong sounds. With weak sounds, the base of the stirrup vibrates mainly around a vertical axis. With strong sounds, slipping occurs in the incus-malleus joint, mainly with low-frequency tones, as a result of which the movement of the long process of the malleus is limited. Along with this, the base of the stirrup begins to vibrate predominantly in the horizontal plane, which also weakens the transmission of sound energy.

In addition to the eardrum and the auditory ossicles, the inner ear is protected from excess sound energy by contracting the muscles of the tympanic cavity. When the stapes muscle contracts, when the acoustic impedance of the middle ear increases sharply, the sensitivity of the inner ear to sounds of mainly low frequencies decreases to 45 dB. Based on this, there is an opinion that the stapedius muscle protects the inner ear from excess energy of low-frequency sounds (Undrits V.F. et al., 1962; Moroz B.S., 1978)

The function of the tensor tympani muscle remains poorly understood. It is believed to have more to do with ventilating the middle ear and maintaining normal pressure in the tympanic cavity than with protecting the inner ear. Both intraauricular muscles also contract when opening the mouth and swallowing. At this moment, the sensitivity of the cochlea to the perception of low sounds decreases.

The sound-conducting system of the middle ear functions optimally when the air pressure in the tympanic cavity and mastoid cells is equal to atmospheric pressure. Normally, the air pressure in the middle ear system is balanced with the pressure of the external environment; this is achieved thanks to the auditory tube, which, opening into the nasopharynx, provides air flow into the tympanic cavity. However, the continuous absorption of air by the mucous membrane of the tympanic cavity creates a slightly negative pressure in it, which requires constant equalization with atmospheric pressure. IN calm state The auditory tube is usually closed. It opens when swallowing or yawning as a result of contraction of the muscles of the soft palate (which stretches and elevates the soft palate). When the auditory tube closes as a result of a pathological process, when air does not enter the tympanic cavity, sharply negative pressure occurs. This leads to a decrease in hearing sensitivity, as well as to the transudation of serous fluid from the mucous membrane of the middle ear. Hearing loss in this case, mainly for tones of low and medium frequencies, reaches 20 - 30 dB. Violation of the ventilation function of the auditory tube also affects the intralabyrinthine pressure of the fluids of the inner ear, which in turn impairs the conduction of low-frequency sounds.

Sound waves, causing movement of the labyrinthine fluid, vibrate the main membrane on which the sensitive hair cells of the spiral organ are located. Irritation of hair cells is accompanied by a nerve impulse entering the spiral ganglion, and then along the auditory nerve to the central parts of the analyzer.

The process of obtaining sound information includes the perception, transmission and interpretation of sound. The ear captures and transforms auditory waves into nerve impulses, which are received and interpreted by the brain.

There is a lot in the ear that is not visible to the eye. What we observe is only part of the outer ear - a fleshy-cartilaginous outgrowth, in other words, the auricle. The outer ear consists of the concha and the ear canal, ending at the eardrum, which provides communication between the outer and middle ear, where the hearing mechanism is located.

Auricle directs sound waves into the ear canal, similar to how the ancient Eustachian trumpet directed sound into the pinna. The channel amplifies sound waves and directs them to eardrum. Sound waves hitting the eardrum cause vibrations that are transmitted through three small auditory bones: the malleus, the incus and the stapes. They vibrate in turn, transmitting sound waves through the middle ear. The innermost of these bones, the stapes, is the smallest bone in the body.

Stapes, vibrating, strikes a membrane called the oval window. Sound waves travel through it to the inner ear.

What happens in the inner ear?

There is a sensory part of the auditory process. Inner ear consists of two main parts: the labyrinth and the snail. The part, which starts at the oval window and curves like a real cochlea, acts as a translator, turning sound vibrations into electrical impulses that can be transmitted to the brain.

How does a snail work?

Snail filled with liquid, in which the basilar (main) membrane seems to be suspended, resembling a rubber band, attached at its ends to the walls. The membrane is covered with thousands of tiny hairs. At the base of these hairs are small nerve cells. When the vibrations of the stapes touch the oval window, the fluid and hairs begin to move. The movement of the hairs stimulates nerve cells, which send a message, in the form of an electrical impulse, to the brain through the auditory, or acoustic, nerve.

Labyrinth is a group of three interconnected semicircular canals that control the sense of balance. Each channel is filled with liquid and located at right angles to the other two. So, no matter how you move your head, one or more channels record that movement and transmit the information to the brain.

If you have ever had a cold in your ear or blown your nose too much, so that your ear “clicks”, then a guess arises: the ear is somehow connected with the throat and nose. And that's true. Eustachian tube directly connects the middle ear to the oral cavity. Its role is to allow air into the middle ear, balancing the pressure on both sides of the eardrum.

Impairments and disorders in any part of the ear can impair hearing if they affect the passage and interpretation of sound vibrations.

How does the ear work?

Let's trace the path of the sound wave. It enters the ear through the pinna and is directed through the auditory canal. If the concha is deformed or the canal is blocked, the path of sound to the eardrum is hampered and hearing ability is reduced. If the sound wave successfully reaches the eardrum, but it is damaged, the sound may not reach the auditory ossicles.

Any disorder that prevents the ossicles from vibrating will prevent sound from reaching the inner ear. In the inner ear, sound waves cause fluid to pulsate, moving tiny hairs in the cochlea. Damage to the hairs or the nerve cells to which they are connected will prevent the sound vibrations from being converted into electrical vibrations. But when the sound has successfully turned into an electrical impulse, it still has to reach the brain. It is clear that damage to the auditory nerve or brain will affect the ability to hear.

Why do such disorders and damage occur?

There are many reasons, we will discuss them later. But the most common culprits are foreign objects in the ear, infections, ear diseases, other diseases that cause complications in the ears, head injuries, ototoxic (i.e. poisonous to the ear) substances, changes in atmospheric pressure, noise, age-related degeneration. All of this causes two main types of hearing loss.

The sense of hearing is one of the most important in human life. Hearing and speech together constitute an important means of communication between people and serve as the basis for relationships between people in society. Hearing loss can lead to disturbances in a person's behavior. Deaf children cannot learn full speech.

With the help of hearing, a person picks up various sounds that signal what is happening in the outside world, the sounds of the nature around us - the rustling of the forest, the singing of birds, the sounds of the sea, as well as various musical works. With the help of hearing, the perception of the world becomes brighter and richer.

The ear and its function. Sound, or sound wave, is an alternating rarefaction and condensation of air, spreading in all directions from the sound source. And the source of sound can be any oscillating body. Sound vibrations are perceived by our hearing organ.

The organ of hearing is very complex and consists of the outer, middle and inner ear. The outer ear consists of the pinna and the auditory canal. The ears of many animals can move. This helps the animal to detect where even the quietest sound is coming from. The human ears also serve to determine the direction of sound, although they are not mobile. The auditory canal connects the outer ear to next department- middle ear.

The auditory canal is blocked at the inner end by a tightly stretched eardrum. A sound wave hitting the eardrum causes it to oscillate and vibrate. The higher the sound, the higher the sound, the greater the frequency of vibration of the eardrum. The stronger the sound, the more the membrane vibrates. But if the sound is very weak, barely audible, then these vibrations are very small. The minimum audibility of a trained ear is almost on the border of those vibrations that are created by the random movement of air molecules. This means that the human ear is a unique hearing device in terms of sensitivity.

Behind the eardrum lies the air-filled cavity of the middle ear. This cavity is connected to the nasopharynx by a narrow passage - the auditory tube. When swallowing, air is exchanged between the pharynx and the middle ear. A change in outside air pressure, for example on an airplane, causes an unpleasant sensation - “stuffy ears”. It is explained by the deflection of the eardrum due to the difference between atmospheric pressure and pressure in the middle ear cavity. When swallowing, the auditory tube opens and the pressure on both sides of the eardrum is equalized.

In the middle ear there are three small bones connected in series: the malleus, the incus and the stirrup. The malleus, connected to the eardrum, transmits its vibrations first to the anvil, and then the increased vibrations are transmitted to the stirrup. In the plate separating the cavity of the middle ear from the cavity of the inner ear, there are two windows covered with thin membranes. One window is oval, with a stirrup “knocking” on it, the other is round.

Behind the middle ear begins the inner ear. It is located deep in the temporal bone of the skull. The inner ear is a system of labyrinths and convoluted canals filled with fluid. There are two organs in the labyrinth: the organ of hearing - the cochlea and the organ of balance - the vestibular apparatus. The cochlea is a spirally twisted bone canal that has two and a half turns in humans. Vibrations of the membrane of the oval window are transmitted to the fluid filling the inner ear. And it, in turn, begins to oscillate with the same frequency. Vibrating, the liquid irritates the auditory receptors located in the cochlea. The cochlear canal is divided in half along its entire length by a membranous septum. Part of this partition consists of a thin membrane - a membrane. On the membrane there are perceptive cells - auditory receptors. Fluctuations in the fluid filling the cochlea irritate individual auditory receptors. They generate impulses that are transmitted along the auditory nerve to the brain. The diagram shows all the sequential processes of converting a sound wave into a nervous signal. Auditory perception. The brain distinguishes between the strength, height and nature of sound, and its location in space. We hear with both ears, and this is of great importance in determining the direction of sound. If sound waves arrive simultaneously in both ears, then we perceive the sound in the middle (front and back). If sound waves arrive a little earlier in one ear than in the other, then we perceive sound either from the right or from the left.