The path of the auditory signal. The process of sound waves passing through the organ of hearing
Peripheral part auditory analyzer In humans, it is morphologically united with the peripheral part of the vestibular analyzer, and morphologists call this structure organelukha and balance (organum vestibulo-cochleare). It has three sections:
- external ear (external auditory canal, auricle with muscles and ligaments);
- middle ear (tympanic cavity, mastoid appendages, auditory tube)
- inner ear(membranous labyrinth located in the bony labyrinth inside the pyramid of the temporal bone).
1. The outer ear concentrates sound vibrations and directs them to the external auditory opening.
2. The auditory canal conducts sound vibrations to the eardrum
3. The eardrum is a membrane that vibrates when exposed to sound.
4. The malleus with its handle is attached to the center of the eardrum with the help of ligaments, and its head is connected to the incus (5), which, in turn, is attached to the stapes (6).
Tiny muscles help transmit sound by regulating the movement of these ossicles.
7. The Eustachian (or auditory) tube connects the middle ear to the nasopharynx. When the ambient air pressure changes, the pressure on both sides of the eardrum is equalized through the auditory tube.
8. Vestibular system. The vestibular system in our ear is part of the body's balance system. Sensory cells provide information about the position and movement of our head.
9. The cochlea is the organ of hearing directly connected to the auditory nerve. The name of the snail is determined by its spirally convoluted shape. This is a bone canal that forms two and a half turns of a spiral and is filled with fluid. The anatomy of the cochlea is very complex, and some of its functions are still unexplored.
The organ of Corti consists of a number of sensory, hair-bearing cells (12) that cover the basilar membrane (13). Sound waves are picked up by hair cells and converted into electrical impulses. These electrical impulses are then transmitted along the auditory nerve (11) to the brain. The auditory nerve consists of thousands of tiny nerve fibers. Each fiber starts from a specific part of the cochlea and transmits a specific sound frequency. Low-frequency sounds are transmitted through fibers emanating from the apex of the cochlea (14), and high-frequency sounds are transmitted through fibers connected to its base. Thus, the function of the inner ear is to convert mechanical vibrations into electrical ones, since the brain can only perceive electrical signals.
Outer ear is a sound-collecting device. The external auditory canal conducts sound vibrations to the eardrum. The eardrum, which separates the outer ear from the tympanic cavity, or middle ear, is a thin (0.1 mm) partition shaped like an inward funnel. The membrane vibrates with action sound vibrations, coming to her through the external auditory canal.
Sound vibrations are picked up by the ears (in animals they can turn towards the sound source) and transmitted through the external auditory canal to the eardrum, which separates the outer ear from the middle ear. Catching sound and the entire process of listening with two ears - so-called binaural hearing - is important for determining the direction of sound. Sound vibrations coming from the side reach the nearest ear a few ten-thousandths of a second (0.0006 s) earlier than the other. This insignificant difference in the time of arrival of sound to both ears is enough to determine its direction.
Middle ear is a sound-conducting device. It is an air cavity that connects through the auditory (Eustachian) tube to the cavity of the nasopharynx. Vibrations from the eardrum through the middle ear are transmitted by 3 auditory ossicles connected to each other - the hammer, incus and stapes, and the latter, through the membrane of the oval window, transmits these vibrations to the fluid located in the inner ear - perilymph.
Due to the geometric features auditory ossicles vibrations of the tympanic membrane 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.
With strong sounds, special muscles reduce the mobility of the eardrum and auditory ossicles, adapting hearing aid to such changes in the stimulus and protecting the inner ear from destruction.
Thanks to the connection of the air cavity of the middle ear with the cavity of the nasopharynx through the auditory tube, it becomes possible to equalize the pressure on both sides of the eardrum, which prevents its rupture during significant changes in pressure in the external environment - when diving under water, climbing to a height, shooting, etc. This is the barofunction of the ear .
There are two muscles in the middle ear: the tensor tympani and the stapedius. The first of them, contracting, increases the tension of the eardrum and thereby limits the amplitude of its vibrations during strong sounds, and the second fixes the stapes and thereby limits its movements. The reflex contraction of these muscles occurs 10 ms after the onset of a strong sound and depends on its amplitude. This automatically protects the inner ear from overload. For instantaneous strong irritations (impacts, explosions, etc.) this defense mechanism does not have time to work, which can lead to hearing impairment (for example, among bombers and artillerymen).
Inner ear is a sound-perceiving apparatus. It is located in the pyramid of the temporal bone and contains the cochlea, which in humans forms 2.5 spiral turns. The cochlear canal is divided by two partitions, the main membrane and the vestibular membrane into 3 narrow passages: upper (scala vestibular), middle (membranous canal) and lower (scala tympani). At the top of the cochlea there is an opening that connects the upper and lower canals into a single one, going from the oval window to the top of the cochlea and then to the round window. Its cavity is filled with fluid - peri-lymph, and the cavity of the middle membranous canal is filled with a fluid of a different composition - endolymph. In the middle channel there is a sound-perceiving apparatus - the organ of Corti, in which there are mechanoreceptors of sound vibrations - hair cells.
The main route of delivery of sounds to the ear is airborne. The approaching sound vibrates the eardrum, and then through the chain of auditory ossicles the vibrations are transmitted to oval window. At the same time, vibrations of the air in the tympanic cavity also arise, which are transmitted to the membrane of the round window. Another way of delivering sounds to the cochlea is fabric or bone conduction . In this case, the sound directly acts on the surface of the skull, causing it to vibrate. Bone pathway for sound transmission becomes of great importance if a vibrating object (for example, the stem of a tuning fork) comes into contact with the skull, as well as in diseases of the middle ear system, when the transmission of sounds through the chain of auditory ossicles is disrupted. In addition to the air path for conducting sound waves, there is a tissue, or bone, path. Under the influence of air sound vibrations, as well as when vibrators (for example, a bone telephone or a bone tuning fork) come into contact with the integument of the head, the bones of the skull begin to vibrate (the bone labyrinth also begins to vibrate) . Based on the latest data (Bekesy and others), it can be assumed that sounds propagating along the bones of the skull only excite the organ of Corti if, similar to air waves, they cause arching of a certain section of the main membrane. The ability of the skull bones to conduct sound explains why to the person himself his voice, recorded on tape, seems alien when the recording is played back, while others easily recognize it. The fact is that the tape recording does not reproduce your entire voice. Usually, when talking, you hear not only those sounds that your interlocutors also hear (i.e., those sounds that are perceived due to air-liquid conduction), but also those low-frequency sounds, the conductor of which is the bones of your skull. However, when listening to a tape recording of your own voice, you hear only what could be recorded - sounds whose conductor is air. Binaural hearing . Humans and animals have spatial hearing, that is, the ability to determine the position of a sound source in space. This property is based on the presence of binaural hearing, or listening with two ears. It is also important for him to have two symmetrical halves at all levels of the auditory system. 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 the neurons of the auditory system to evaluate interaural (interaural) differences in the time of sound arrival on the right and left ear and sound intensity 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.
30504 1
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, the basis of which is the analysis and synthesis of non-verbal and verbal audio information containing natural and artificial sounds in environment and speech symbols - words reflecting the material world and human mental activity. Hearing as a function sound analyzer — most important factor in 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 among its constituent frequencies, and ruled, when the sound consists of a set 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 sounds produced by musical instruments have multiple frequencies and human voice. 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 hearing threshold to 10 3 N/m 2 at the loudest sounds, for example, noise produced jet engine. The subjective characteristic of hearing is associated with sound intensity - sound volume and many others quality characteristics 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 propagation speed. 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 wide range 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) ) is shown in Fig. 1 general scheme sound transmission systems.
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 malleus; 6, 10 - scala vestibule; 7, 9 - cochlear duct; 8 - cochlear part of the vestibulocochlear nerve; 11 - scala tympani; 12 - auditory tube; 13 - cochlear window, 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 sound transmission process 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 outer hole ear canal 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 The ears 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 not affected by the diameter of the existing or resulting pathological process narrowing of the ear canal, and 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 gravis, 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 conduction: 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 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-topic principle“cable” transmission of a nerve signal to 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 adequate stimulus 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 bioelectrical impulses generated only by fibers auditory nerve in response to sound stimulation. 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 effect of quinine, streptomycin and a number of other factors that disrupt homeostasis internal environments cochlea, violate the ratio of magnitudes and signs of 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. From a clinical point of view, it seems very important that these cells are highly sensitive to oxygen deficiency, changes in the level of carbon dioxide and sugar in the liquid media of the cochlea, and disturbances in ionic equilibrium. These changes can lead to parabiotic reversible or irreversible pathomorphological changes in the receptor apparatus of the cochlea and to corresponding disorders of 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. By the first we mean 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 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 established 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 area of its middle part, and a sound of 1002 Hz is shifted towards the main curl so much that between the sections of these frequencies there is one unexcited cell for which a corresponding frequency “was not found.” 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.
Psychophysical laws of sound perception form psycho physiological functions 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 injury ear or auditory centers), then these sensations in their essence approach spontaneous ones.
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 selection mechanism useful information, on the other hand, the interference suppression mechanism. 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 essential functions complex biological systems — adaptation.
Adaptation is biological mechanism, with the help of 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 loud sounds. Increased 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 level is more than high level, 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 testing adaptation 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 when differential diagnosis peripheral and central lesions of the hearing organ. When the cerebral hemispheres are damaged, various disorders ototopics. 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 hearing theories developed in late XIX- early 20th century
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 spatial perception separate 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
There are 2 ways to conduct sound:
Based on the ability of a sound wave to propagate in solids. The bones of the skull conduct sound well. But the significance of this path for healthy person not great. But if air route is broken, then this path cannot be replaced. With the help of a sound apparatus, receptor irritation is achieved bypassing the air threshold.
2) Air
In this path, sound passes through:
· Auricle – external auditory canal – tympanic membrane – auditory ossicles – oval window – cochlea – fluid canals – nervous apparatus – round window.
Peripheral department analyzer. Represented by the organ of hearing – the ear. Highlight:
External ear (pinna, external auditory canal.
· The ears are a mouthpiece and contribute to the concentration of sounds emanating from different parts of space in the direction of the external auditory canal.
· Restrict flow sound signals, coming from the rear.
· Perform a protective function, protecting the eardrum from thermal and mechanical influences. Provide temperature constant and humidity in this area.
The boundary between the outer and middle parts of the ear is the eardrum.
It has the shape of a cone with the apex directed into the middle ear cavity.
Functions:
· Provides transmission of vibrations to the middle ear, through the system of auditory ossicles.
Middle ear. Represented by the tympanic cavity and the ossicular hearing system
Functions:
· Conductive – conduction of sound. The malleus, incus and stapes form a lever that increases the pressure applied to the eardrum by 20 times.
· Protective, providing 2 muscles
1) Muscle that stretches the tympanic membrane
2) The stapedalis muscle, when contracted, fixes the stapes, limiting its movement
The function of these muscles is that, by contracting, they reduce the amplitude of vibrations of the eardrum and ossicles and thereby reduce the coefficient of sound pressure transmission to the inner ear. The cut occurs at sounds above 90 dB, but the cut has a latency period of 10 milliseconds that is too long.
When exposed to immediate strong stimuli, this mechanism does not work. During the action of prolonged sounds, it plays an important role. Contraction of the stipendial muscle is observed during the action of a new stimulus, yawning, swallowing and speech activity.
The middle ear is connected to the back of the pharynx by a narrow canal called the eustachian tube. The function is to balance the pressure in the middle ear and the external environment.
Inner ear. Organ of hearing. Located in the cochlea, spirally twisted in shape. The cochlea is divided into three channels:
In the middle of the canal on the basilar membrane is the Gordian organ. Gordian organ - system cross fibers, the main membrane and sensitive striatal cells located on this membrane. Vibrations of the fibers, the main membrane, are transmitted to the hair cells, in which contact with the tectorial membrane overhanging them causes a receptor potential. Nerve impulses generated by hair cells are transmitted along the cochlear nerve to higher centers sound analyses.
The number of receptors tuned to a certain frequency changes.
Auditory pathways.
along the axon of the nerve cells of the spiral ganglion approaching the receptor cells is transmitted to the auditory center of the medulla oblongata. Cochliary nuclei. After switching on the cells of the cochliary nuclei, electrical impulses enter the nuclei of the superior olive, here the first crossover of the auditory pathways is noted: a minority of the fibers remain on the sides auditory receptor, most of it goes to the opposite side. Next, the information passes through the medial geniculate. body and is transmitted to the superior temporal gyrus. Where the auditory sensation is formed.
Bilural hearing. Provides localization of the stimulus due to the non-simultaneous propagation of the sound wave to each ear.
Interaction with other organs and systems.
Somatic – sentinel reflex Visceral
taste system, is a chemoreceptive system that analyzes chemical stimuli operating at the taste level.
Taste- this is a sensation that occurs as a result of the influence of a substance on the receptors. Located on the surface of the tongue and oral mucosa. Taste is a contact type of sensitivity. Taste is a multimodal sensory experience. There are 4 tastes of sensitivity: sweet, sour, salty, bitter. Tip tongue - sweet, the root is bitter, the side surfaces are sour and salty.
The taste threshold depends on the concentration of the substance. The lowest is bitter, sweet is higher, the threshold for sour and salty is close to sweet. The intensity depends on the size of the tongue surface and temperature. With prolonged exposure to receptors, adaptation occurs and the threshold increases significantly.
Prescription machine.
Taste buds are located in the form of complexes, taste buds (about 2000). Consisting of 40-60 receptor cells. Each taste bud contains about 50 nerve fibers. Taste buds are located in taste buds having a different structure and located on the tongue. There are 3 types of papillae:
1) Mushroom-shaped. Located on all surfaces of the tongue
2) Gutters. Back, root
3) Leaf-shaped. Along the posterior edges of the tongue.
The taste bud excites due to the interaction of stimuli with receptor molecules located on the stimulus membrane.
Olfactory system.
Performs the perception and analysis of chemical stimuli located in the external environment and acting on the olfactory organs.
Smell is the perception by organisms of certain properties of substances using the olfactory organs.
Classification of odors.
There are 7 main smells:
1) Camphoraceae-eucalyptus
2) Essential - pear
3) Musk-musk
4) Floral – rose
5) Putrid - rotten eggs
6) Caustic – vinegar
7) Mint – mint
The receptor apparatus is represented by the olfactory epithelium. Olfactory receptors have cytoplasmic outgrowths - cilia. This allows you to increase the area of smell by 100-150 times. The molecules of the odorous substance coincide with the ultramicroscopic structure of the olfactory cells, like a key and a lock. This interaction leads to a change in membrane permeability, its defoliation and the development of a nerve impulse. The axons united in a bundle go to the olfactory bulb, from there as part of the olfactory tract to many brain structures, the nucleus of the third brain, limbic system hypothalamus.
Vestibular analyzer
Sensory system, which perceives, transmits and analyzes information about the spatial orientation of the body and ensures the implementation of tonic, complexly coordinated reflexes.
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?
This is where the sensory part of the auditory process takes place. 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 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 you have a guess that the ear is somehow connected with the throat and nose. And that's true. Eustachian tube directly connects the middle ear to 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.
The auricle, external auditory canal, tympanic membrane, auditory ossicles, annular ligament of the oval window, membrane of the round window (secondary tympanic membrane), labyrinthine fluid (perilymph), and the main membrane take part in the conduction of sound vibrations.
In humans, the role of the auricle is relatively small. In animals that have the ability to move their ears, the pinnae help determine the direction of the source of sound. In humans, the auricle, like a megaphone, only collects sound waves. However, in this respect its role is insignificant. Therefore, when a person listens to quiet sounds, he puts his palm to his ear, due to which the surface of the auricle significantly increases.
Sound waves, having penetrated the auditory canal, set the eardrum into friendly vibration, which transmits sound vibrations through the chain of auditory ossicles to the oval window and further to the perilymph of the inner ear.
The eardrum responds not only to those sounds whose number of vibrations coincides with its own tone (800-1000 Hz), but also to any sound. This resonance is called universal, in contrast to acute resonance, when a secondary sounding body (for example, a piano string) responds to only one specific tone.
The eardrum and auditory ossicles do not simply transmit sound vibrations entering the external auditory canal, but transform them, that is, they transform air vibrations with large amplitude and low pressure into vibrations of the labyrinth fluid with low amplitude and high pressure.
This transformation is achieved due to the following conditions: 1) the surface of the tympanic membrane is 15-20 times larger than the area of the oval window; 2) the malleus and incus form an unequal lever, so that the excursions made by the foot plate of the stapes are approximately one and a half times less than the excursions of the malleus handle.
The overall effect of the transformative effect of the eardrum and the lever system of the auditory ossicles is expressed in an increase in sound intensity by 25-30 dB. Disruption of this mechanism in case of damage to the eardrum and diseases of the middle ear leads to a corresponding decrease in hearing, i.e., by 25-30 dB.
For the normal functioning of the eardrum and the chain of auditory ossicles, it is necessary that the air pressure on both sides of the eardrum, i.e. in the external auditory canal and in the tympanic cavity, be the same.
This pressure equalization occurs due to the ventilation function of the auditory tube, which connects the tympanic cavity to the nasopharynx. With each swallowing movement, air from the nasopharynx enters the tympanic cavity, and thus the air pressure in the tympanic cavity is always maintained at atmospheric level, i.e. at the same level as in the external auditory canal.
The sound-conducting apparatus also includes the muscles of the middle ear, which perform following functions: 1) maintaining the normal tone of the eardrum and the chain of auditory ossicles; 2) protection of the inner ear from excessive sound stimulation; 3) accommodation, i.e. adaptation of the sound-conducting apparatus to sounds of varying strength and height.
When the muscle that stretches the tympanic membrane contracts, auditory sensitivity increases, which gives reason to consider this muscle “alert.” The stapedius muscle plays the opposite role - when it contracts, it limits the movements of the stirrup and thereby, as it were, muffles sounds that are too strong.
The mechanism described above for transmitting sound vibrations from external environment To inner ear through the external auditory canal, eardrum and chain of auditory ossicles represents airborne sound conduction. But sound can be delivered to the inner ear bypassing a significant part of this path, namely directly through the bones of the skull - bone sound conduction. Under the influence of fluctuations in the external environment, oscillatory movements of the bones of the skull, including the bony labyrinth, occur. These1 oscillatory movements are transmitted to the fluid of the labyrinth (perilymph). The same transmission occurs when a sounding body, for example the leg of a tuning fork, comes into direct contact with the bones of the skull, as well as under the influence of high-frequency sounds with a small vibration amplitude.
The presence of bone conduction of sound vibrations can be verified through simple experiments: 1) when both ears are tightly plugged with fingers, i.e., when the access of air vibrations through the external auditory canals is completely stopped, the perception of sounds deteriorates significantly, but still occurs; 2) if the stem of a sounding tuning fork is placed against the crown of the head or the mastoid process, then the sound of the tuning fork will be clearly audible even with the ears plugged.
Bone sound conduction has special meaning in ear pathology. Thanks to this mechanism, the perception of sounds is ensured, although in a sharply weakened form, in cases where the transmission of sound vibrations through the outer and middle ear completely stops. Bone sound conduction is carried out, in particular, in case of complete blockage of the external auditory canal (for example, with cerumen), as well as in diseases that lead to immobility of the chain of auditory ossicles (for example, with otosclerosis).
As already mentioned, vibrations of the tympanic membrane are transmitted through the chain of ossicles to the oval window and cause movements of the perilymph, which spread along the scala vestibule to the scala tympani. These fluid movements are possible due to the presence of the round window membrane (secondary tympanic membrane), which, with each inward movement of the stapes plate and the corresponding push of the perilymph, protrudes towards the tympanic cavity. As a result of movements of the perilymph, vibrations of the main membrane and the organ of Corti located on it occur.