Hearing analyzer(auditory sensory system) is the second most important distant human analyzer. Hearing plays a vital role in humans in connection with the emergence of articulate speech. Acoustic (sound) signals are air vibrations with different frequencies and strength. They stimulate auditory receptors located in the cochlea inner ear. The receptors activate the first auditory neurons, after which sensory information is transmitted to auditory area cerebral cortex (temporal) through a number of sequential structures.

The organ of hearing (ear) is a peripheral section of the auditory analyzer in which auditory receptors are located. The structure and functions of the ear are presented in table. 12.2, fig. 12.10.

Table 12.2.

Structure and functions of the ear

Ear part	Structure	Functions
Outer ear	Auricle, external ear canal, eardrum	Protective (sulfur release). Captures and transmits sounds. Sound waves oscillate eardrum, and she is the auditory ossicles.
Middle ear	An air-filled cavity containing the auditory ossicles (hammer, incus, stapes) and the Eustachian (auditory) tube	The auditory ossicles conduct and amplify sound vibrations 50 times. The Eustachian tube, connected to the nasopharynx, equalizes pressure on the eardrum
Inner ear	Organ of hearing: oval and round windows, cochlea with a cavity filled with fluid, and organ of Corti - sound-receiving apparatus	Auditory receptors located in the organ of Corti convert sound signals into nerve impulses that are transmitted to the auditory nerve and then to the auditory cortex cerebral hemispheres
	Organ of balance ( vestibular apparatus): three semicircular canals, otolithic apparatus	Perceives the position of the body in space and transmits impulses to the medulla oblongata, then to the vestibular zone of the cerebral cortex; response impulses help maintain body balance

Rice. 12.10. Organs hearing And equilibrium. External, middle and inner ear, as well as the auditory and vestibular (vestibular) branches of the vestibulocochlear nerve (VIII pair) extending from the receptor elements of the organ of hearing (organ of Corti) and balance (crests and spots) cranial nerves).

The mechanism of sound transmission and perception. Sound vibrations are picked up by the auricle and transmitted through the external auditory canal to the eardrum, which begins to vibrate in accordance with the frequency of the sound waves. Vibrations of the eardrum are transmitted to the chain of ossicles of the middle ear and, with their participation, to the membrane oval window. Vibrations of the membrane of the vestibule window are transmitted to the perilymph and endolymph, which causes vibrations of the main membrane along with the organ of Corti located on it. In this case, the hair cells touch the integumentary (tectorial) membrane with their hairs, and due to mechanical irritation, excitation arises in them, which is transmitted further to the fibers of the vestibulocochlear nerve (Fig. 12.11).

Rice. 12.11. Membranous channel And spiral (Corti) organ. The cochlear canal is divided into the scala tympani and vestibular canal and the membranous canal (middle scala), in which the organ of Corti is located. The membranous canal is separated from the scala tympani by a basilar membrane. It contains peripheral processes of neurons of the spiral ganglion, forming synaptic contacts with outer and inner hair cells.

Location and structure of receptor cells of the organ of Corti. On the main membrane there are two types of receptor hair cells: internal and external, separated from each other by the arches of Corti.

The inner hair cells are arranged in a single row; the total number of them along the entire length membranous canal reaches 3,500. Outer hair cells are arranged in 3-4 rows; their total number is 12,000-20,000. Each hair cell has an elongated shape; one of its poles is fixed on the main membrane, the second is located in the cavity of the membranous canal of the cochlea. There are hairs at the end of this pole, or stereocilia. Their number on each internal cell is 30-40 and they are very short - 4-5 microns; on each outer cell the number of hairs reaches 65-120, they are thinner and longer. The hairs of the receptor cells are washed by the endolymph and come into contact with the integumentary (tectorial) membrane, which is located above the hair cells along the entire course of the membranous canal.

The mechanism of auditory reception. When exposed to sound, the main membrane begins to vibrate, the longest hairs of the receptor cells (stereocilia) touch the integumentary membrane and tilt slightly. Deviation of the hair by several degrees leads to tension in the thinnest vertical filaments (microfilaments) connecting the tops of neighboring hairs of a given cell. This tension, purely mechanically, opens from 1 to 5 ion channels in the stereocilium membrane. A potassium ion current begins to flow through the open channel into the hair. The tension force of the thread required to open one channel is negligible, about 2·10 -13 newton. What seems even more surprising is that the weakest sounds felt by humans stretch the vertical filaments connecting the tops of neighboring stereocilia to a distance half the diameter of a hydrogen atom.

The fact that the electrical response of the auditory receptor reaches a maximum after only 100-500 μs (microseconds) means that the membrane ion channels open directly from the mechanical stimulus without the participation of intracellular second messengers. This distinguishes mechanoreceptors from much slower-acting photoreceptors.

Depolarization of the presynaptic ending of the hair cell leads to the release of a neurotransmitter (glutamate or aspartate) into the synaptic cleft. By acting on the postsynaptic membrane of the afferent fiber, the mediator causes the generation of excitation of the postsynaptic potential and further generation of impulses propagating in the nerve centers.

The opening of just a few ion channels in the membrane of one stereocilium is clearly not enough to generate a receptor potential of sufficient magnitude. An important mechanism for amplifying the sensory signal at the receptor level of the auditory system is the mechanical interaction of all stereocilia (about 100) of each hair cell. It turned out that all stereocilia of one receptor are connected to each other in a bundle by thin transverse filaments. Therefore, when one or more of the longer hairs bends, they pull all the other hairs with them. As a result, the ion channels of all hairs open, providing a sufficient magnitude of the receptor potential.

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 of two symmetrical halves of the auditory analyzer (binaural hearing).

The acuity of binaural hearing in humans is very high: he is able to determine the location of a sound source with an accuracy of about 1 angular degree. Physiological basis This is achieved by the ability of the neural structures of the auditory analyzer to evaluate interaural (interaural) differences in sound stimuli by the time of their arrival at each ear and by their intensity. If the sound source is away from midline head, the sound wave arrives at one ear somewhat earlier and with greater force than at the other. Assessing the distance of a sound from the body is associated with a weakening of the sound and a change in its timbre.

The auditory analyzer includes three main parts: the organ of hearing, auditory nerves, subcortical and cortical centers of the brain. Not many people know how a hearing analyzer works, but today we will try to figure it out together.

A person recognizes the world around him and adapts to society thanks to his senses. One of the most important are the hearing organs, which pick up sound vibrations and provide a person with information about what is happening around him. The set of systems and organs that provide the sense of hearing is called the auditory analyzer. Let's look at the structure of the organ of hearing and balance.

The structure of the auditory analyzer

The functions of the auditory analyzer, as mentioned above, are to perceive sound and provide information to a person, but despite all the simplicity at first glance, this is a rather complex procedure. In order to better understand how the sections of the auditory analyzer work in the human body, you need to thoroughly understand What is the internal anatomy of the auditory analyzer?

The hearing analyzer includes:

• the receptor (peripheral) apparatus is, and;
• conduction (middle) apparatus – auditory nerve;
• central (cortical) apparatus - auditory centers in temporal lobes cerebral hemispheres.

The hearing organs in children and adults are identical; they include three types of hearing aid receptors:

• receptors that perceive vibrations of air waves;
• receptors that give a person an idea of ​​the location of the body;
• receptor centers that allow you to perceive the speed of movement and its direction.

The hearing organ of each person consists of 3 parts; by examining each of them in more detail, you can understand how a person perceives sounds. So, this is the totality of the auditory canal. The shell is a cavity made of elastic cartilage that is covered with a thin layer of skin. Outer ear represents a certain amplifier for conversion sound vibrations. The ears are located on both sides human head and they don’t play a role, since they simply collect sound waves. motionless, and even if their outer part is missing, then special harm the structure of the human auditory analyzer will not receive.

Considering the structure and functions of the external auditory canal, we can say that it is a small canal 2.5 cm long, which is lined with skin with small hairs. The canal contains apocrine glands that are capable of producing earwax, which, together with hairs, helps protect the following parts of the ear from dust, pollution and foreign particles. The outer part of the ear only helps to collect sounds and conduct them into central department auditory analyzer.

Eardrum and middle ear

It looks like a small oval with a diameter of 10 mm; a sound wave passes through it into the inner ear, where it creates some vibrations in the liquid, which fills this section of the human auditory analyzer. There is a system in the human ear to transmit air vibrations; it is their movements that activate the vibration of the liquid.

Between the outer part of the hearing organ and internal department is located . This section of the ear looks like a small cavity, with a capacity of no more than 75 ml. This cavity is connected to the pharynx, cells mastoid process And auditory tube, which is a kind of fuse that equalizes the pressure inside and outside the ear. I would like to note that the eardrum is always subjected to the same atmospheric pressure both outside and inside, this allows the organ of hearing to function normally. If there is a difference between the pressures inside and outside, then hearing acuity will be impaired.

Structure of the inner ear

The most complex part of the auditory analyzer is the “labyrinth”. The main receptor apparatus that picks up sounds is the hair cells of the inner ear or, as they also say, “cochlea”.

The conductive section of the auditory analyzer consists of 17,000 nerve fibers, which resemble the structure telephone cable with separately insulated wires, each of which transmits specific information to neurons. It is the hair cells that respond to vibrations of the fluid inside the ear and transmit nerve impulses in the form of acoustic information to the peripheral part of the brain. And the peripheral part of the brain is responsible for the sensory organs.

Ensures fast transfer nerve impulses conducting paths of the auditory analyzer. To put it simply, the pathways of the auditory analyzer connect the hearing organ with the human central nervous system. Excitement auditory nerve activate motor pathways that are responsible, for example, for eye twitching due to strong sound. The cortical section of the auditory analyzer connects the peripheral receptors of both sides, and when capturing sound waves, this section compares sounds from both ears at once.

The mechanism of sound transmission at different ages

The anatomical characteristics of the auditory analyzer do not change at all with age, but I would like to note that there are certain age-related features.

The hearing organs begin to form in the embryo at the 12th week of development. The ear begins to function immediately after birth, but initial stages Human auditory activity is more like reflexes. Sounds of different frequency and intensity cause different reflexes in children, this can be closing their eyes, shuddering, opening their mouth or rapid breathing. If a newborn reacts this way to distinct sounds, then it is clear that the auditory analyzer is developed normally. In the absence of these reflexes, additional research is required. Sometimes the child’s reaction is inhibited by the fact that initially the middle ear of the newborn is filled with some kind of fluid that interferes with movement auditory ossicles, over time, the specialized liquid dries out completely and air fills the middle ear instead.

The baby begins to differentiate different sounds from 3 months, and at the 6th month of life he begins to distinguish tones. At 9 months of life, a child can recognize the voices of his parents, the sound of a car, the singing of a bird and other sounds. Children begin to identify a familiar and alien voice, recognize it and begin to hoot, rejoice, or even look with their eyes for the source of their native sound if it is not nearby. The development of the auditory analyzer continues until the age of 6 years, after which the child’s hearing threshold decreases, but at the same time hearing acuity increases. This continues for up to 15 years, then works in the opposite direction.

In the period from 6 to 15 years, you can notice that the level of hearing development is different, some children catch sounds better and are able to repeat them without difficulty, they manage to sing well and copy sounds. Other children are less successful at this, but at the same time they hear perfectly; such children are sometimes called “the bear is in his ear.” Communication between children and adults is of great importance; it is this that shapes the child’s speech and musical perception.

Regarding anatomical features, then in newborns the auditory tube is much shorter than in adults and wider, because of this, infection from respiratory tract so often affects their hearing organs.

Sound perception

For the auditory analyzer, sound is an adequate stimulus. The main characteristics of each sound tone are frequency and amplitude sound wave.

The higher the frequency, the higher the pitch of the sound. The strength of a sound, expressed by its volume, is proportional to the amplitude and is measured in decibels (dB). Human ear capable of perceiving sound in the range from 20 Hz to 20,000 Hz (children - up to 32,000 Hz). The ear is most excitable to sounds with a frequency from 1000 to 4000 Hz. Below 1000 and above 4000 Hz, the excitability of the ear is greatly reduced.

A sound of up to 30 dB is very faintly audible, from 30 to 50 dB corresponds to a person’s whisper, from 50 to 65 dB to ordinary speech, from 65 to 100 dB to strong noise, 120 dB to “ pain threshold", and 140 dB - causes damage to the middle (rupture of the eardrum) and inner (destruction of the organ of Corti) ear.

The speech hearing threshold for children 6-9 years old is 17-24 dBA, for adults - 7-10 dBA. With the loss of the ability to perceive sounds from 30 to 70 dB, difficulties are observed when speaking; below 30 dB, almost complete deafness is stated.

At long-term action in the ear of strong sounds (2-3 minutes), hearing acuity decreases, and in silence it is restored; 10-15 seconds are enough for this (auditory adaptation).

Changes in hearing aid over the lifespan

The age characteristics of the auditory analyzer change slightly throughout a person’s life.

In newborns, the perception of pitch and volume of sound is reduced, but by 6–7 months, sound perception reaches the adult norm, although the functional development of the auditory analyzer, associated with the development of subtle differentiations to auditory stimuli, continues until 6–7 years. The greatest hearing acuity is characteristic of adolescents and young men (14–19 years old), then gradually decreases.

In old age auditory perception changes its frequency. Thus, in childhood the sensitivity threshold is much higher, it is 3200 Hz. From 14 to 40 years old we are at a frequency of 3000 Hz, and at 40-49 years old we are at 2000 Hz. After 50 years, only at 1000 Hz, it is from this age that the upper limit of audibility begins to decrease, which explains deafness in old age.

Older people often have blurred perception or intermittent speech, that is, they hear with some interference. They can hear part of the speech well, but miss a few words. In order for a person to hear normally, he needs both ears, one of which perceives sound, and the other maintains balance. As a person ages, the structure of the eardrum changes; it may be affected by certain factors compact, which will upset the balance. As for gender sensitivity to sounds, men lose hearing much faster than women.

I would like to note that with special training, even in old age, you can achieve an increase in the hearing threshold. Similarly, exposure to loud noise in a constant mode, which can negatively affect auditory system even at a young age. In order to avoid the negative consequences of constant exposure to loud sound on the human body, you need to monitor. This is a set of measures aimed at creating normal conditions for functioning auditory organ. In people young the critical noise limit is 60 dB, and in children school age critical threshold 60 dB. It is enough to stay in a room with this noise level for an hour and negative consequences will not keep you waiting.

One more age-related changes hearing aid is the fact that over time, earwax hardens, this prevents the normal vibration of air waves. If a person has a tendency to cardiovascular diseases. It is likely that blood will circulate faster in damaged vessels, and as a person ages, he will be able to hear extraneous noises in the ears.

Modern medicine has long figured out how the auditory analyzer works and is very successfully working on hearing aids, which make it possible to restore hearing to people after 60 years of age and enable children with defects in the development of the auditory organ to live a full life.

The physiology and operation of the auditory analyzer is very complex, and it is very difficult for people without the appropriate skills to understand it, but in any case, every person should be theoretically familiar.

Now you know how the receptors and sections of the auditory analyzer work.

List of used literature:

• A. A. Drozdov “ENT diseases: lecture notes”, ISBN: 978-5-699-23334-2;
• Palchun V.T. " Short course otorhinolaryngology: a guide for doctors." ISBN: 978-5-9704-3814-5;
• Shvetsov A.G. Anatomy, physiology and pathology of the organs of hearing, vision and speech: Tutorial. Veliky Novgorod, 2006

Prepared under the editorship of A.I. Reznikov, doctor of the first category

The receptive part of the auditory analyzer is the ear, the conductive part is the auditory nerve, and the central part is the auditory zone of the cerebral cortex. The hearing organ consists of three sections: the outer, middle and inner ear. The ear includes not only the organ of hearing itself, with the help of which auditory sensations are perceived, but also the organ of balance, due to which the body is held in a certain position.

The outer ear consists of the pinna and the external auditory canal. The shell is formed by cartilage covered on both sides by skin. With the help of a shell, a person catches the direction of sound. The muscles that move the auricle are rudimentary in humans. The external auditory canal looks like a tube 30 mm long, lined with skin, in which there are special glands that secrete earwax. In the depths, the ear canal is covered with a thin oval-shaped eardrum. On the side of the middle ear, in the middle of the eardrum, the handle of the hammer is strengthened. The membrane is elastic; when struck by sound waves, it repeats these vibrations without distortion.

The middle ear is represented by the tympanic cavity, which communicates with the nasopharynx through the auditory (Eustachian) tube; It is delimited from the outer ear by the eardrum. The components of this department are: hammer, anvil And stapes. With its handle, the malleus fuses with the eardrum, while the anvil is articulated with both the malleus and the stirrup, which covers the oval hole leading to the inner ear. In the wall separating the middle ear from the inner ear, in addition to the oval window, there is also a round window covered with a membrane.
Structure of the hearing organ:
1 - auricle, 2 - external auditory canal,
3 - eardrum, 4 - middle ear cavity, 5 - auditory tube, 6 - cochlea, 7 - semicircular canals, 8 - anvil, 9 - hammer, 10 - stapes

The inner ear, or labyrinth, is located deep in the temporal bone and has double walls: membranous labyrinth as if inserted into bone, repeating its shape. The gap-like space between them is filled clear liquid - perilymph, cavity of the membranous labyrinth - endolymph. Labyrinth presented the threshold anterior to it is the cochlea, posteriorly - semicircular canals. The cochlea communicates with the middle ear cavity through a round window covered by a membrane, and the vestibule communicates through the oval window.

The organ of hearing is the cochlea, its remaining parts make up the organs of balance. The cochlea is a spirally twisted canal of 2 3/4 turns, separated by a thin membranous septum. This membrane is spirally curled and is called basic. It consists of fibrous tissue, which includes about 24 thousand special fibers (auditory strings) of different lengths and located transversely along the entire course of the cochlea: the longest are at its apex, and the shortest at the base. Overhanging these fibers are auditory hair cells - receptors. This is the peripheral end of the auditory analyzer, or organ of Corti. The hairs of the receptor cells face the cavity of the cochlea - the endolymph, and the auditory nerve originates from the cells themselves.

Perception of sound stimuli. Sound waves passing through the external auditory canal cause vibrations in the eardrum and are transmitted to the auditory ossicles, and from them to the membrane of the oval window leading to the vestibule of the cochlea. The resulting vibration sets in motion the perilymph and endolymph of the inner ear and is perceived by the fibers of the main membrane, which carries the cells of the organ of Corti. High-pitched sounds with a high vibration frequency are perceived by short fibers located at the base of the cochlea and transmitted to the hairs of the cells of the organ of Corti. In this case, not all cells are excited, but only those located on fibers of a certain length. Therefore, the primary analysis sound signals begins already in the organ of Corti, from which excitation along the fibers of the auditory nerve is transmitted to the auditory center of the cerebral cortex in temporal lobe, where their qualitative assessment takes place.

Vestibular apparatus. The vestibular apparatus plays an important role in determining the position of the body in space, its movement and speed of movement. It is located in the inner ear and consists of vestibule and three semicircular canals, located in three mutually perpendicular planes. The semicircular canals are filled with endolymph. In the endolymph of the vestibule there are two sacs - round And oval with special lime stones - statolites, adjacent to the hair receptor cells of the sacs.

In normal body position, the statoliths irritate the hairs of the lower cells with their pressure; when the body position changes, the statoliths also move and irritate other cells with their pressure; the received impulses are transmitted to the cerebral cortex. In response to irritation of the vestibular receptors associated with the cerebellum and the motor zone of the cerebral hemispheres, muscle tone and body position in space reflexively change. Three semicircular canals extend from the oval sac, which initially have extensions - ampoules, in which hair cells - receptors are located. Since the channels are located in three mutually perpendicular planes, the endolymph in them, when the body position changes, irritates certain receptors, and the excitation is transmitted to the corresponding parts of the brain. The body reflexively responds with the necessary change in body position.

Hearing hygiene. Earwax accumulates in the external auditory canal and traps dust and microorganisms, so it is necessary to regularly wash your ears with warm soapy water; Under no circumstances should you remove sulfur with hard objects. Overfatigue of the nervous system and overstrain of hearing can cause sharp sounds and noises. Prolonged noise is especially harmful, causing hearing loss and even deafness. Loud noise reduces labor productivity by up to 40-60%. To combat noise in industrial environments, walls and ceilings are lined with special materials that absorb sound, and individual noise-reducing headphones are used. Motors and machines are installed on foundations that muffle the noise from the shaking of the mechanisms.

Human hearing is designed to pick up wide range sound waves and convert them into electrical impulses to be sent to the brain for analysis. Unlike the vestibular apparatus associated with the organ of hearing, which functions normally almost from birth, hearing takes a long time to develop. The formation of the auditory analyzer ends no earlier than at 12 years of age, and the greatest hearing acuity is achieved by the age of 14-19 years. the auditory analyzer has three sections: the peripheral or organ of hearing (ear); conductive, including nerve pathways; cortical, located in the temporal lobe of the brain. Moreover, in the cerebral cortex there are several auditory centers. Some of them (inferior temporal gyri) are designed to perceive more simple sounds- tones and noises, others are associated with complex sound sensations that arise while a person speaks himself, listens to speech or music.

The structure of the human ear The human auditory analyzer perceives sound waves with an oscillation frequency of 16 to 20 thousand per second (16-20000 hertz, Hz). The upper sound threshold for an adult is 20,000 Hz; lower threshold – ranging from 12 to 24 Hz. Children have a higher upper limit of hearing around 22,000 Hz; in older people, on the contrary, it is usually lower - about 15,000 Hz. The ear is most sensitive to sounds with frequencies ranging from 1000 to 4000 Hz. Below 1000 Hz and above 4000 Hz, the excitability of the hearing organ is greatly reduced. The ear is a complex vestibular-auditory organ. Like all our sense organs, the human hearing organ performs two functions. It perceives sound waves and is responsible for the position of the body in space and the ability to maintain balance. This paired organ, which is located in the temporal bones of the skull, limited externally by the auricles. Receptive devices for hearing and vestibular system located in the inner ear. The structure of the vestibular system can be viewed separately, but now let’s move on to a description of the structure of the parts of the hearing organ.

The organ of hearing consists of 3 parts: the outer, middle and inner ear, with the outer and middle ear playing the role of a sound-conducting apparatus, and the inner ear - a sound-receiving apparatus. The process begins with sound - the oscillatory movement of air or vibration in which sound waves travel towards the listener, eventually reaching the eardrum. At the same time, our ear is extremely sensitive and can sense pressure changes of only 1-10 atmospheres.

Structure of the external ear The external ear consists of the auricle and the external auditory canal. First, sound reaches the ears, which act as receivers of sound waves. The auricle is formed by elastic cartilage, covered on the outside with skin. Determining the direction of sound in humans is associated with binaural hearing, i.e. with hearing with two ears. Any lateral sound reaches one ear before the other. The difference in time (several fractions of a millisecond) of arrival of sound waves perceived by the left and right ears makes it possible to determine the direction of the sound. In other words, our natural perception of sound is stereophonic.

The human auricle has its own unique relief of convexities, concavities and grooves. This is necessary for the finest acoustic analysis, also allowing you to recognize the direction and source of sound. 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 source. Thus, the brain receives additional information to clarify the location of the sound source. This effect is sometimes used in acoustics, including to create a sense of surround sound when designing speakers and headphones. The auricle also amplifies sound waves, which then enter the external auditory canal - the space from the concha to the eardrum about 2.5 cm long and about 0.7 cm in diameter. The auditory canal has a weak resonance at a frequency of about 3000 Hz.

One more interesting characteristic external auditory canal is the presence of earwax, which is constantly secreted from the glands. Earwax is a waxy secretion of 4000 sebaceous and sulfur glands of the ear canal. Its function is to protect the skin of this passage from bacterial infection and foreign particles or, for example, insects that may get into the ear. U different people the amount of sulfur varies. If there is an excessive accumulation of sulfur, a sulfur plug may form. If the ear canal is completely blocked, there is a feeling of ear congestion and decreased hearing, including the resonance of one’s own voice in the blocked ear. These disorders develop suddenly, most often when water gets into the external auditory canal while swimming.

The outer and middle ears are separated by the eardrum, which is a thin connective tissue plate. The thickness of the eardrum is about 0.1 mm, and the diameter is about 9 millimeters. On the outside it is covered with epithelium, and on the inside with mucous membrane. The eardrum is located obliquely and begins to vibrate when sound waves hit it. The eardrum is extremely sensitive, but once vibration is detected and transmitted, the eardrum returns to its original position in just 0.005 seconds.

The structure of the middle ear In our ear, sound moves to the sensitive cells that perceive sound signals through a matching and amplifying device - the middle ear. The middle ear is a tympanic cavity, which has the shape of a small flat drum with a tightly stretched vibrating membrane and an auditory (Eustachian) tube. In the cavity of the middle ear there are auditory ossicles that articulate with each other - the hammer, incus and stapes. Tiny muscles help transmit sound by regulating the movement of these ossicles. When the sound reaches the eardrum, it vibrates. The handle of the hammer is woven into the eardrum and, by swaying, it sets the hammer in motion. The other end of the malleus is connected to the incus, and the latter is movably articulated with the stapes using a joint. The stapes muscle is attached to the stapes, which holds it against the membrane of the oval window (vestibulary window), which separates the middle ear from the inner ear, filled with fluid. As a result of the transmission of movement, the stapes, the base of which resembles a piston, is constantly pushed into the membrane of the oval window of the inner ear.

The function of the auditory ossicles is to provide an increase in the pressure of the sound wave when transmitted from the eardrum to the membrane of the oval window. This amplifier (about 30-40 times) helps weak sound waves incident on the eardrum overcome the resistance of the oval window membrane and transmit vibrations to the inner ear. When a sound wave passes from air environment In liquid, a significant part of the sound energy is lost and, therefore, a sound amplification mechanism is necessary. However, with a loud sound, the same mechanism reduces the sensitivity of the entire system so as not to damage it.

The air pressure inside the middle ear must be the same as the pressure outside the eardrum to ensure normal vibration conditions. To equalize pressure, the tympanic cavity is connected to the nasopharynx using an auditory (Eustachian) tube 3.5 cm long and about 2 mm in diameter. When swallowing, yawning, and chewing, the Eustachian tube opens to let in outside air. 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. Malfunction of the tube leads to pain and even bleeding in the ear.

Structure of the inner ear. Mechanical movements ossicles in the inner ear are converted into electrical signals. Inner ear - hollow bone formation in the temporal bone, divided into bone canals and cavities containing the receptor apparatus of the auditory analyzer and the organ of balance. Because of its intricate shape, this section of the organ of hearing and balance is called the labyrinth. The bony labyrinth consists of the vestibule, cochlea and semicircular canals, but only the cochlea is directly related to hearing. The cochlea is a canal about 32 mm long, coiled and filled with lymphatic fluids. Having received vibration from the eardrum, the stapes, with its movement, presses on the membrane of the vestibule window and creates pressure fluctuations inside the cochlear fluid. This vibration travels through the fluid of the cochlea and reaches the organ of hearing itself, the spiral or organ of Corti. It turns the vibrations of the liquid into electrical signals that go through the nerves to the brain. In order for the stapes to transmit pressure through the fluid, in the central part of the labyrinth, the vestibule, there is a round window of the cochlea, covered with a flexible membrane. When the piston of the stapes enters the oval window of the vestibule, the membrane of the cochlear window bulges under the pressure of the cochlear fluid. Oscillations in a closed cavity are possible only in the presence of recoil. The role of such return is performed by the membrane of the round window.

The bony labyrinth of the cochlea is wrapped in the shape of a spiral with 2.5 turns and contains inside a membranous labyrinth of the same shape. In some places, the membranous labyrinth is attached to the periosteum of the bony labyrinth by connecting cords. Between the bony and membranous labyrinth there is a fluid - perilymph. The sound wave, amplified by 30-40 dB using the eardrum - auditory ossicles system, reaches the window of the vestibule, and its vibrations are transmitted to the perilymph. The sound wave first passes through the perilymph to the top of the spiral, where through the hole the vibrations propagate to the window of the cochlea. Inside, the membranous labyrinth is filled with another fluid - endolymph. The fluid inside the membranous labyrinth (cochlear duct) is separated from the perilymph above by a flexible covering plate, and below by an elastic main membrane, which together make up the membranous labyrinth. On the main membrane there is a sound-receiving apparatus, the organ of Corti. The main membrane consists of large quantity(24,000) fibrous fibers of various lengths, stretched like strings. These fibers form an elastic network, which as a whole resonates in strictly graded vibrations.

Nerve cells the organ of Corti is converted oscillatory movements plates into electrical signals. They are called hair cells. Inner hair cells are arranged in one row, there are 3.5 thousand of them. Outer hair cells are arranged in three to four rows, there are 12–20 thousand of them. Each hair cell has an elongated shape, it has 60–70 tiny hairs (stereocilia) 4–5 µm long.

All sound energy is concentrated in the space limited by the wall of the bony cochlea and the main membrane (the only pliable place). The main membrane fibers have different lengths and, accordingly, different resonant frequencies. The shortest fibers are located near the oval window, their resonant frequency is about 20,000 Hz. The longest ones are at the top of the spiral and have a resonant frequency of about 16 Hz. It turns out that each hair cell, depending on its location on the main membrane, is tuned to a certain audio 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 for some reason, a person loses the ability to perceive sounds of the corresponding frequencies.

The sound wave propagates through the perilymph from the window of the vestibule to the window of the cochlea almost instantly, in about 4 * 10-5 seconds. Caused by this wave hydrostatic pressure moves the integumentary plate relative to the surface of the organ of Corti. As a result, the integumentary plate deforms the bundles of stereocilia of the hair cells, which leads to their excitation, which is transmitted to the endings of the primary sensory neurons.

Differences in the ionic composition of endolymph and perilymph create a potential difference. And between the endolymph and the intracellular environment of the receptor cells, the potential difference reaches approximately 0.16 volts. Such a significant potential difference contributes to the excitation of hair cells even under the influence of weak sound signals, causing slight vibrations of the main membrane. When the stereocilia of hair cells are deformed, a receptor potential arises in them, which leads to the release of a regulator that acts on the endings of the auditory nerve fibers and thereby excites them.

Hair cells are connected to the endings of nerve fibers that, upon exiting the organ of Corti, form the auditory nerve (cochlear branch of the vestibulocochlear nerve). Sound waves, converted into electrical impulses, are transmitted along the auditory nerve to the temporal zone of the cerebral cortex.

The auditory nerve consists of thousands of tiny nerve fibers. Each of them starts from a certain part of the cochlea and, thereby, transmits a certain sound frequency. Each fiber of the auditory nerve is associated with several hair cells, so that the central nervous system about 10,000 fibers arrive. Impulses from low-frequency sounds are transmitted through fibers emanating from the top of the cochlea, and from high-frequency sounds - 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.

The organ of hearing is the apparatus through which we receive sound information. But we hear the way our brain perceives, processes and remembers. Sound ideas or images are created in the brain. And, if music sounds in our head or someone’s voice is remembered, then due to the fact that the brain has input filters, a storage device and sound card, and can be both a boring speaker and a convenient music center for us.

Age anatomy and physiology Antonova Olga Aleksandrovna

5.5. Hearing analyzer

5.5. Hearing analyzer

The main function of the hearing organs is the perception of air vibrations. The organs of hearing are closely related to the organs of balance. The receptor apparatus of the auditory and vestibular systems are located in the inner ear.

Phylogenetically they have common origin. Both receptor apparatuses are innervated by fibers of the third pair of cranial nerves, both respond to physical indicators: the vestibular apparatus perceives angular accelerations, auditory – air vibrations.

Auditory perceptions are very closely related to speech - a child who has lost hearing in early childhood, loses speech ability, although speech apparatus he is absolutely normal.

In the embryo, the hearing organs develop from the auditory vesicle, which first communicates with outer surface body, but as the embryo develops it is detached from skin and forms three semicircular canals located in three mutually perpendicular planes. The part of the primary auditory vesicle that connects these canals is called the vestibule. It consists of two chambers - oval (uterus) and round (sac).

IN lower section In the vestibule, a hollow protrusion or tongue is formed from thin membranous chambers, which in the embryos is extended and then curled in the form of a snail. The uvula forms the organ of Corti (the receptive part of the hearing organ). This process occurs in the 12th week intrauterine development, and at the 20th week myelination of the auditory nerve fibers begins. IN recent months intrauterine development, cell differentiation begins in the cortical part of the auditory analyzer, which occurs especially intensively in the first two years of life. The formation of the auditory analyzer ends by the age of 12-13.

Organ of hearing. The human hearing organ consists of the outer ear, middle ear and inner ear. The outer ear serves to capture sounds; it is formed by the auricle and the external auditory canal. The auricle is formed by elastic cartilage, covered on the outside with skin. The auricle is padded at the bottom skin fold- lobe, which is filled with adipose tissue. Determining the direction of sound in a person is associated with binaural hearing, that is, hearing with two ears. Any lateral sound reaches one ear before the other. The difference in time (several fractions of a millisecond) of arrival of sound waves perceived by the left and right ears makes it possible to determine the direction of the sound. When one ear is affected, a person determines the direction of sound by rotating the head.

The external auditory canal in an adult has a length of 2.5 cm, a capacity of 1 cubic meter. see The skin lining the ear canal has fine hairs and modified sweat glands that produce earwax. They perform protective role. Earwax is made up of fat cells that contain pigment.

The outer and middle ears are separated by the eardrum, which is a thin connective tissue plate. The thickness of the eardrum is about 0.1 mm; it is covered with epithelium on the outside and mucous membrane on the inside. The eardrum is located obliquely and begins to vibrate when sound waves hit it. Since the eardrum does not have its own period of vibration, it vibrates with any sound according to its wavelength.

The middle ear is a tympanic cavity, which has the shape of a small flat drum with a tightly stretched vibrating membrane and an auditory tube. In the cavity of the middle ear there are auditory ossicles that articulate with each other - the hammer, incus and stapes. The handle of the hammer is woven into the eardrum; at the other end the malleus is connected to the incus, and the latter is movably articulated with the stapes using a joint. The stapes muscle is attached to the stapes, which holds it against the membrane of the oval window, which separates the inner ear from the middle ear. The function of the auditory ossicles is to provide an increase in the pressure of the sound wave when transmitted from the tympanic membrane to the membrane of the oval window. This increase (about 30–40 times) helps weak sound waves incident on the eardrum overcome the resistance of the oval window membrane and transmit vibrations to the inner ear, transforming there into endolymph vibrations.

The tympanic cavity is connected to the nasopharynx using an auditory (Eustachian) tube 3.5 cm long, very narrow (2 mm), maintaining equal pressure from the outside and inside on the eardrum, thereby ensuring the most favorable conditions for her to hesitate. The opening of the tube in the pharynx is most often in a collapsed state, and air passes into the tympanic cavity during the act of swallowing and yawning.

The inner ear is located in the petrous part of the temporal bone and is a bony labyrinth, inside of which there is a membranous labyrinth of connective tissue, which seems to be inserted into the bone labyrinth and repeats its shape. Between the bony and membranous labyrinths there is a fluid - perilymph, and inside the membranous labyrinth - endolymph. In addition to the oval window, in the wall separating the middle ear from the inner ear, there is a round window that allows fluid to vibrate.

The bony labyrinth consists of three parts: in the center is the vestibule, in front of it is the cochlea, and behind it is the semicircular canals. The bony cochlea is a spirally twisting canal that forms two and a half turns around the rod conical shape. The diameter of the bone canal at the base of the cochlea is 0.04 mm, at the apex – 0.5 mm. A bone spiral plate extends from the rod, which divides the canal cavity into two parts - scalae.

Inside the middle canal of the cochlea is the spiral organ of Corti. It has a basilar (main) plate, consisting of approximately 24 thousand thin fibrous fibers of various lengths. These fibers are very elastic and weakly connected to each other. On the main plate along it in five rows there are supporting and hair sensitive cells - these are the auditory receptors.

The inner hair cells are arranged in one row, there are 3.5 thousand of them along the entire length of the membranous canal. The outer hair cells are arranged in three to four rows, there are 12–20 thousand of them. Each receptor cell has an elongated shape, there are 60–70 tiny hairs (4–5 microns long). The hairs of the receptor cells are washed by the endolymph and come into contact with the integumentary plate, which hangs over them. Hair cells are covered nerve fibers cochlear branch of the auditory nerve. IN medulla oblongata the second neuron of the auditory pathway is located; Then the way goes, crossing, to the posterior tubercles of the quadrigeminal, and from them - to the temporal region of the cortex, where it is located central part auditory analyzer.

The cerebral cortex contains several auditory centers. Some of them (the inferior temporal gyri) are designed to perceive simpler sounds - tones and noises. Others are associated with the most complex sound sensations that arise while a person speaks himself, listens to speech or music.

Mechanism of sound perception. For the auditory analyzer, sound is an adequate stimulus. Sound waves arise as alternating condensations and rarefactions of air and propagate in all directions from the sound source. All vibrations of air, water or other elastic medium break down into periodic (tones) and non-periodic (noise).

Tones are high and low. Low tones correspond to fewer vibrations per second. Each sound tone is characterized by the length of the sound wave, which corresponds to a certain number of vibrations per second: than larger number oscillations, the shorter the wavelength. High sounds have a short wavelength, measured in millimeters. The wavelength of low sounds is measured in meters.

The upper sound threshold for an adult is 20,000 Hz; the lowest is 12–24 Hz. Children have a higher upper limit of hearing - 22,000 Hz; in older people it is lower - about 15,000 Hz. The ear is most sensitive to sounds with frequencies ranging from 1000 to 4000 Hz. Below 1000 Hz and above 4000 Hz, the excitability of the ear is greatly reduced.

In newborns, the middle ear cavity is filled with amniotic fluid. This makes it difficult for the auditory ossicles to vibrate. Over time, the liquid resolves, and instead from the nasopharynx through eustachian tube air penetrates. A newborn baby shudders at loud sounds, his breathing changes, and he stops crying. Children's hearing becomes clearer by the end of the second - beginning of the third month. After two months, the child differentiates qualitatively different sounds; at 3–4 months, he distinguishes the pitch of sounds; at 4–5 months, sounds become conditioned reflex stimuli for him. By the age of 1–2 years, children distinguish sounds with a difference of one or two, and by four to five years, even 3/4 and 1/2 musical tones.