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 picks up and converts auditory waves into nerve impulses, which the brain receives and interprets.

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 inner ear?

There goes the sensory part 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 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 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 most often, 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 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 necessary processes occur auditory perception 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 eardrum, 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 also creates vibrations of the eardrum 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 membrane, 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 inward-facing scala medial surfaces of the hair cells are covered plasma membrane sensitive hairs - 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. Endocochlear potential plays important role in the stimulation of hair cells. It is assumed that hair cells are polarized by this potential to a 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. It is in the latter case that the auditory receptors are irritated. 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. 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. Axons of neurons in the auditory nuclei ascend into overlying structures auditory analyzer both ipsilaterally 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 the 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 of 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 signs of the 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 efferent influences are involved in the exacerbation of the frequency-threshold curve already at the level 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 excitation thresholds 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.

IN central departments In 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 the eardrum (7 * 10"6). The latter circumstance increases the pressure of the sound wave on the eardrum by approximately 22 times (70:3.2)

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 the reflex adaptation of the auditory organ to the intensity of sound.

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 is reflexively reduced. As a result, on the one hand, the possibility of its traumatic rupture is reduced, and on the other, the intensity of vibration of the ossicles 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 varying 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 much loud noise 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 excited, as a rule, by entire 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 oscillation 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, the physiological significance of the 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 labyrinthine pressure inside 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 come 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 the anatomical structure of the organ of Corti, which resembles 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 biphasic 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. Komendantov, 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 proposes, for preventive purposes, to “disinhibit” workers in noisy enterprises 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 a 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 the question is decided in what type of production a person can work in and in which he cannot.

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 depends entirely 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, Bottom part- lobe of the auricle - lobe, 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 hammer - 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 bone 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 human body, 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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From a functional point of view, the hearing organ (the peripheral part of the auditory analyzer) is divided into two parts:
1) sound-conducting apparatus - the outer and middle ear, as well as some elements (perilymph and endolymph) of the inner ear;
2) sound-receiving apparatus - the inner ear.

Air waves collected by the auricle are directed into the external auditory canal, hitting the eardrum and causing it to vibrate. Vibration of the eardrum, the degree of tension of which is regulated by contraction of the muscle tensor tympani septum, sets in motion the handle of the hammer fused to it. The malleus accordingly moves the incus, and the incus moves the stirrup, which is inserted into the foramen vovale leading into the inner ear. The amount of displacement of the stapes in the window of the vestibule is regulated by contraction of the stapedius muscle. Thus, the chain of ossicles, connected movably, transmits the oscillatory movements of the tympanic membrane towards the window of the vestibule.

The movement of the stapes in the window of the vestibule inside causes movement of the labyrinthine fluid, which protrudes the membrane of the window of the cochlea outward. These movements are necessary for the functioning of the highly sensitive elements of the spiral organ. The perilymph of the vestibule moves first; its vibrations along the vestibular scala ascend to the top of the cochlea, are transmitted through the helicotrema to the perilymph into the scala tympani, descend along it to the membrane covering the window of the cochlea, which is a weak point in the bone wall of the inner ear, and, as it were, return to the tympanic cavity. From the perilymph, sound vibration is transmitted to the endolymph, and through it to the spiral organ. Thus, air vibrations in the outer and middle ear, thanks to the system of auditory ossicles of the tympanic cavity, turn into vibrations of the fluid of the membranous labyrinth, causing irritation of special auditory hair cells of the spiral organ, which make up the receptor of the auditory analyzer.

In the receptor, which is like a “reverse” microphone, mechanical vibrations of the fluid (endolymph) are converted into electrical ones, characterizing the nervous process that spreads along the conductor to the cerebral cortex.

Fig.23. Diagram of sound vibrations.

Dendrites of hair (bipolar) sensory cells, which are part of the spiral ganglion, located right there in the central part of the cochlea, approach the auditory hairs. The axons of the bipolar (hair) cells of the spiral (cochlear) ganglion form the auditory branch of the vestibulocochlear nerve (VIII pair of cranial nerves), going to the nuclei of the auditory analyzer located in the bridge (second auditory neuron), subcortical auditory centers in the quadrigeminal region (third auditory neuron) and the cortical hearing center in the temporal lobe of each hemisphere (Fig. 9), where auditory sensations are formed. There are approximately 30,000–40,000 afferent fibers in the auditory nerve. Vibrating hair cells cause excitation only in strictly defined fibers of the auditory nerve, and therefore in strictly defined nerve cells cerebral cortex. Each hemisphere receives information from both ears (binaural hearing), making it possible to determine the source of sound and its direction. If the sounding object is on the left, then impulses from the left ear arrive in the brain earlier than from the right. This small difference in time allows not only to determine the direction, but also to perceive sound sources from different parts of space. This sound is called surround or stereophonic.

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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.

Thus, sound, in a broad sense, is elastic waves propagating in some 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 is the different temperature of 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 altitudes they move not only at different speeds, but sometimes in 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 vary 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 in the environment, such as 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 an important biological significance, for example, sound waves in the range of 300-4000 Hz correspond to 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. This way the brain gets 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 ossicles: 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, and cells tuned to low frequencies, are located in the upper part of the cochlea, and high frequencies are picked up by cells in the lower part 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 felt through the senses 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, concussion, 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 world around us can be felt by an ordinary person through the use of certain narcotic substances.

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 depression. 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 disturbed and distorted.

The Hearing and Balance Organ is the peripheral part of the Gravity, Balance and Hearing Analyzer. It is located within one anatomical formation - the labyrinth and consists of the outer, middle and inner ear (Fig. 1).

Rice. 1. (diagram): 1 - external auditory canal; 2 - auditory tube; 3 - eardrum; 4 - hammer; 5 - anvil; 6 - snail.

1. Outer ear(auris externa) consists of the auricle (auricula), external auditory canal (meatus acusticus externus), and eardrum (membrana tympanica). The outer ear plays the role of the auditory funnel to capture and conduct sound.

Between the external auditory canal and the tympanic cavity is the eardrum (membrana tympanica). The eardrum is elastic, low-elastic, thin (0.1-0.15 mm thick), and concave inward in the center. The membrane has three layers: dermal, fibrous and mucous. It has a loose part (pars flaccida) - Shrapnel membrane, which does not have a fibrous layer, and a tense part (pars tensa). For practical purposes, the membrane is divided into squares.

2. Middle ear(auris media) consists of the tympanic cavity (cavitas tympani), auditory tube (tuba auditiva) and mastoid cells (cellulae mastoideae). The middle ear is a system of air cavities in the thickness of the petrous part of the temporal bone.

Tympanic cavity has a vertical dimension of 10 mm and a transverse dimension of 5 mm. The tympanic cavity has 6 walls (Fig. 2): lateral - membranous (paries membranaceus), medial - labyrinthine (paries labyrinthicus), anterior - carotid (paries caroticus), posterior - mastoid (paries mastoideus), superior - tegmental (paries tegmentalis) ) and lower - jugular (paries jugularis). Often in top wall there are cracks in which the mucous membrane of the tympanic cavity is adjacent to the dura mater.

Rice. 2. : 1 - paries tegmentalis; 2 - paries mastoideus; 3 - paries jugularis; 4 - paries caroticus; 5 - paries labyrinthicus; 6 - a. carotis interna; 7 - ostium tympanicum tubae auditivae; 8 - canalis facialis; 9 - aditus ad antrum mastoideum; 10 - fenestra vestibuli; 11 - fenestra cochleae; 12 - n. tympanicus; 13 - v. jugularis interna.

The tympanic cavity is divided into three floors; supratympanic recess (recessus epitympanicus), middle (mesotympanicus) and lower - subtympanic recess (recessus hypotympanicus). In the tympanic cavity there are three auditory ossicles: the malleus, the incus and the stapes (Fig. 3), two joints between them: the incus-malleus (art. incudomallcaris) and the incudostapedialis (art. incudostapedialis), and two muscles: the tensor tympani ( m. tensor tympani) and stirrup (m. stapedius).

Rice. 3. : 1 - malleus; 2 - incus; 3 - steps.

Eustachian tube- channel 40 mm long; has a bony part (pars ossea) and a cartilaginous part (pars cartilaginea); connects the nasopharynx and the tympanic cavity with two openings: ostium tympanicum tubae auditivae and ostium pharyngeum tubae auditivae. During swallowing movements, the slit-like lumen of the tube expands and freely passes air into the tympanic cavity.

3. Inner ear(auris interna) has a bony and membranous labyrinth. Part bony labyrinth(labyrinthus osseus) included semicircular canals, vestibule And cochlea canal(Fig. 4).

Membranous labyrinth(labyrinthus membranaceus) has semicircular ducts, little queen, pouch And cochlear duct(Fig. 5). Inside the membranous labyrinth there is endolymph, and outside there is perilymph.

Rice. 4.: 1 - cochlea; 2 - cupula cochleae; 3 - vestibulum; 4 - fenestra vestibuli; 5 - fenestra cochleae; 6 - crus osseum simplex; 7 - crura ossea ampullares; 8 - crus osseum commune; 9 - canalis semicircularis anterior; 10 - canalis semicircularis posterior; 11 - canali semicircularis lateralis.

Rice. 5. : 1 - ductus cochlearis; 2 - sacculus; 3 - utriculus; 4 - ductus semicircularis anterior; 5 - ductus semicircularis posterior; 6 - ductus semicircularis lateralis; 7 - ductus endolymphaticus in aquaeductus vestibuli; 8 - saccus endolymphaticus; 9 - ductus utriculosaccularis; 10 - ductus reuniens; 11 - ductus perilymphaticus in aquaeductus cochleae.

The endolymphatic duct, located in the aqueduct of the vestibule, and the endolymphatic sac, located in the cleft of the dura mater, protect the labyrinth from excessive vibrations.

On a cross section of the bony cochlea, three spaces are visible: one endolymphatic and two perilymphatic (Fig. 6). Because they climb up the coils of the cochlea, they are called staircases. The median staircase (scala media), filled with endolymph, has a triangular outline in cross-section and is called the cochlear duct (ductus cochlearis). The space located above the cochlear duct is called the scala vestibuli; the space located below is the scala tympani.

Rice. 6. : 1 - ductus cochlearis; 2 - scala vestibuli; 3 - modiolus; 4 - ganglion spirale cochleae; 5 - peripheral processes of ganglion spirale cochleae cells; 6 - scala tympani; 7 - bone wall of the cochlear canal; 8 - lamina spiralis ossea; 9 - membrane vestibularis; 10 - organum spirale seu organum Cortii; 11 - membrane basilaris.

Sound path

Sound waves are captured by the auricle, sent to the external auditory canal, causing vibrations of the eardrum. The vibrations of the membrane are transmitted by the system of auditory ossicles to the window of the vestibule, then to the perilymph along the scala vestibule to the apex of the cochlea, then through the lucid window, the helicotrema, to the perilymph of the scala tympani and are attenuated, hitting the secondary tympanic membrane in the cochlear window (Fig. 7).

Rice. 7. : 1 - membrana tympanica; 2 - malleus; 3 - incus; 4 - steps; 5 - membrana tympanica secundaria; 6 - scala tympani; 7 - ductus cochlearis; 8 - scala vestibuli.

Through the vestibular membrane of the cochlear duct, vibrations of the perilymph are transmitted to the endolymph and the main membrane of the cochlear duct, on which the receptor of the auditory analyzer, the organ of Corti, is located.

Conducting path of the vestibular analyzer

Receptors of the vestibular analyzer: 1) ampullary scallops (crista ampullaris) - perceive the direction and acceleration of movement; 2) spot of the uterus (macula utriculi) - gravity, position of the head at rest; 3) sac spot (macula sacculi) - vibration receptor.

The bodies of the first neurons are located in the vestibular node, g. vestibulare, which is located at the bottom of the internal auditory canal (Fig. 8). The central processes of the cells of this node form the vestibular root of the eighth nerve, n. vestibularis, and end on the cells of the vestibular nuclei of the eighth nerve - the bodies of the second neurons: upper core- core V.M. Bekhterev (there is an opinion that only this nucleus has a direct connection with the cortex), medial(main) - G.A Schwalbe, lateral-O.F.C. Deiters and lower- Ch.W. Roller. The axons of the cells of the vestibular nuclei form several bundles that are sent to the spinal cord, the cerebellum, the medial and posterior longitudinal fasciculi, and also to the thalamus.

Rice. 8.: R - receptors - sensitive cells of the ampullary combs and cells of the spots of the utricle and sac, crista ampullaris, macula utriculi et sacculi; I - first neuron - cells of the vestibular node, ganglion vestibulare; II - second neuron - cells of the superior, inferior, medial and lateral vestibular nuclei, n. vestibularis superior, inferior, medialis et lateralis; III - third neuron - lateral nuclei of the thalamus; IV - cortical end of the analyzer - cells of the cortex of the inferior parietal lobule, middle and inferior temporal gyri, Lobulus parietalis inferior, gyrus temporalis medius et inferior; 1 - spinal cord; 2 - bridge; 3 - cerebellum; 4 - midbrain; 5 - thalamus; 6 - internal capsule; 7 - area of ​​the cortex of the inferior parietal lobule and the middle and inferior temporal gyri; 8 - vestibulospinal tract, tractus vestibulospinalis; 9 - motor nucleus cell anterior horn spinal cord; 10 - cerebellar tent nucleus, n. fastigii; 11 - vestibulocerebellar tract, tractus vestibulocerebellaris; 12 - to the medial longitudinal fasciculus, reticular formation and vegetative center of the medulla oblongata, fasciculus longitudinalis medialis; formatio reticularis, n. dorsalis nervi vagi.

The axons of the cells of the Deiters and Roller nuclei enter the spinal cord, forming the vestibulospinal tract. It ends on the cells of the motor nuclei of the anterior horns of the spinal cord (the bodies of the third neurons).

The axons of the cells of the Deiters, Schwalbe and Bechterew nuclei are sent to the cerebellum, forming the vestibulocerebellar tract. This pathway passes through the inferior cerebellar peduncles and ends at the cells of the cerebellar vermis cortex (the body of the third neuron).

The axons of the cells of the Deiters nucleus are sent to the medial longitudinal fasciculus, which connects the vestibular nuclei with the nuclei of the third, fourth, sixth and eleventh cranial nerves and ensures that the direction of gaze is maintained when the head position changes.

From Deiters' nucleus, axons are also sent to the posterior longitudinal fasciculus, which connects the vestibular nuclei with the autonomic nuclei of the third, seventh, ninth and tenth pairs of cranial nerves, which explains autonomic reactions in response to excessive stimulation of the vestibular apparatus.

Nerve impulses to the cortical end of the vestibular analyzer pass as follows. The axons of the cells of the Deiters and Schwalbe nuclei pass to the opposite side as part of the vestibular tract to the bodies of the third neurons - the cells of the lateral nuclei of the thalamus. The processes of these cells pass through the internal capsule into the cortex of the temporal and parietal lobes of the hemisphere.

Conducting path of the auditory analyzer

Receptors that perceive sound stimulation are located in the organ of Corti. It is located in the cochlear duct and is represented by sensory hair cells located on the basement membrane.

The bodies of the first neurons are located in the spiral ganglion (Fig. 9), located in the spiral canal of the cochlea. The central processes of the cells of this node form the cochlear root of the eighth nerve (n. cochlearis) and end on the cells of the ventral and dorsal cochlear nuclei of the eighth nerve (the bodies of the second neurons).

Rice. 9.: R - receptors - sensitive cells of the spiral organ; I - first neuron - cells of the spiral ganglion, ganglion spirale; II - second neuron - anterior and posterior cochlear nuclei, n. cochlearis dorsalis et ventralis; III - third neuron - anterior and posterior nuclei of the trapezoid body, n. dorsalis et ventralis corporis trapezoidei; IV - fourth neuron - cells of the nuclei of the inferior colliculi of the midbrain and medial geniculate body, n. colliculus inferior et corpus geniculatum mediale; V - cortical end of the auditory analyzer - cells of the cortex of the superior temporal gyrus, gyrus temporalis superior; 1 - spinal cord; 2 - bridge; 3 - midbrain; 4 - medial geniculate body; 5 - internal capsule; 6 - section of the cortex of the superior temporal gyrus; 7 - roof-spinal tract; 8 - cells of the motor nucleus of the anterior horn of the spinal cord; 9 - fibers of the lateral loop in the loop triangle.

The axons of the cells of the ventral nucleus are directed to the ventral and dorsal nuclei of the trapezoidal body on their own and the opposite side, and the latter form the trapezoidal body itself. The axons of the cells of the dorsal nucleus pass to the opposite side as part of the medullary striae, and then the trapezoid body to its nuclei. Thus, the bodies of third neurons auditory pathway located in the nuclei of the trapezoid body.

The totality of axons of third neurons is lateral loop(lemniscus lateralis). In the isthmus region, the loop fibers lie superficially in the loop triangle. The fibers of the loop end on the cells of the subcortical centers (the bodies of the fourth neurons): the inferior colliculi of the quadrigeminal and the medial geniculate bodies.

The axons of the cells of the nucleus of the inferior colliculus are directed as part of the roof-spinal tract to the motor nuclei of the spinal cord, carrying out unconditioned reflex motor reactions of the muscles to sudden auditory stimulation.

The axons of the cells of the medial geniculate bodies pass through the posterior leg of the internal capsule into the middle part of the superior temporal gyrus - the cortical end of the auditory analyzer.

There are connections between the cells of the nucleus of the inferior colliculus and the cells of the motor nuclei of the fifth and seventh pairs of cranial nuclei, which provide regulation of the work of the auditory muscles. In addition, there are connections between the cells of the auditory nuclei with the medial longitudinal fasciculus, which ensure the movement of the head and eyes when searching for a sound source.

Development of the vestibulocochlear organ

1. Development of the inner ear. The rudiment of the membranous labyrinth appears in the 3rd week of intrauterine development through the formation of thickenings of the ectoderm on the sides of the anlage of the posterior medullary vesicle (Fig. 10).

Rice. 10.: A - stage of formation of auditory placodes; B - stage of formation of auditory pits; B - stage of formation of auditory vesicles; I - first visceral arch; II - second visceral arch; 1 - pharyngeal intestine; 2 - medullary plate; 3 - auditory placode; 4 - medullary groove; 5 - auditory fossa; 6 - neural tube; 7 - auditory vesicle; 8 - first gill pouch; 9 - first gill slit; 10 - growth of the auditory vesicle and formation of the endolymphatic duct; 11 - formation of all elements of the membranous labyrinth.

At stage 1 of development, the auditory placode is formed. At stage 2, an auditory fossa is formed from the placode, and at stage 3, an auditory vesicle is formed. Next, the auditory vesicle lengthens, the endolymphatic duct protrudes from it, which pulls the vesicle into 2 parts. The semicircular ducts develop from the upper part of the vesicle, and the cochlear duct develops from the lower part. Receptors for the auditory and vestibular analyzers are formed in the 7th week. The cartilaginous labyrinth develops from the mesenchyme surrounding the membranous labyrinth. It ossifies in the 5th week of intrauterine development.

2. Middle ear development(Fig. 11).

The tympanic cavity and auditory tube develop from the first gill pouch. Here a single tubular-drum canal is formed. The tympanic cavity is formed from the dorsal part of this canal, and the auditory tube is formed from the dorsal part. From the mesenchyme of the first visceral arch the hammer, incus, m. tensor tympani, and the fifth nerve innervating it, from the mesenchyme of the second visceral arch - the stapes, m. stapedius and the seventh nerve that innervates it.

Rice. 11.: A - location of the visceral arches of the human embryo; B - six tubercles of mesenchyme located around the first external gill slit; B - auricle; 1-5 - visceral arches; 6 - first gill slit; 7 - first gill pouch.

3. Development of the outer ear. The auricle and external auditory canal develop as a result of the fusion and transformation of six tubercles of mesenchyme located around the first external branchial cleft. The pit of the first external gill slit deepens, and a tympanic membrane is formed in its depth. Its three layers develop from three germ layers.

Anomalies in the development of the hearing organ

1. Deafness can be a consequence of underdevelopment of the auditory ossicles, a violation of the receptor apparatus, as well as a violation of the conductive part of the analyzer or its cortical end.
2. Fusion of the auditory ossicles, reducing hearing.
3. Anomalies and deformities of the external ear:
   • anotia - absence of the auricle,
   • buccal auricle,
   • fused lobe,
   • shell consisting of one lobe,
   • concha, located below the ear canal,
   • microtia, macrotia (small or too large ear),
   • atresia of the external auditory canal.

Information . Physiology of VNI and sensory systems . Fundamentals of neurophysiology and GNI .

The peripheral part of the auditory analyzer is morphologically combined in humans with the peripheral part of the vestibular analyzer, and morphologists call this structure the 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).

External ear (external auditory canal, pinna 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.

Organ of Corti

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 under the action of sound vibrations coming to it 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 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.

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 through the auditory tube of the air cavity of the middle ear with the cavity of the nasopharynx, 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. In case of instantaneous strong irritations (impacts, explosions, etc.), this protective 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 the oval window. At the same time, vibrations of the air in the tympanic cavity also occur, which are transmitted to the membrane of the round window.

Another way of delivering sounds to the cochlea is tissue 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. Except air route, there is a tissue, or bone, path for conducting sound waves.

Under the influence of airborne 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 foreign 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 (that is, 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 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.