The passage of sound waves through the ear. Paths of sound to the receptor

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, act on the next ones, and the area high blood pressure as if moving in an elastic medium. The area of ​​high pressure is followed by an area low blood 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 heights they move not only at different speeds, but sometimes at different speeds. different directions. This means that the wind at different heights from the ground may have different speeds and directions. The shape of the sound wave in such layers will also change from layer to layer. Let, for example, the sound come against the wind. In this case, the sound propagation line should bend and go upward. But if a layer of slow-moving air gets in its way, it will change its direction again and may return to the ground again. It is then that in the space from the place where the wave rises in height to the place where it returns to the ground, a “zone of silence” appears.

Organs of sound perception

Hearing - ability biological organisms perceive sounds with the hearing organs; a special function of the hearing aid, excited by sound vibrations 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 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. Thus, the brain receives additional information to clarify the location of the sound source. This effect is sometimes used in acoustics, including to create the sensation of surround sound when using headphones or hearing aids.
The function of the auricle is to catch sounds; its continuation is the cartilage of the external auditory canal, the length of which is on average 25-30 mm. The cartilaginous part of the auditory canal passes into the bone, and the entire external auditory canal is lined with skin containing sebaceous and sulfur glands, which are modified sweat glands. This passage ends blindly: it is separated from the middle ear by the eardrum. Sound waves captured by the auricle hit the eardrum and cause it to vibrate.

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

Middle ear
The main part of the middle ear is the tympanic cavity - a small space with a volume of about 1 cm³, located in temporal bone. There are three here auditory ossicles: hammer, incus and stirrup - they transmit sound vibrations from the outer ear to the inner ear, at the same time 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 fluid, on bottom wall which the receptor apparatus is located 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 sensed through the sense of touch.

The range of loudness of perceived sounds is enormous. But the eardrum in the ear is only sensitive to changes in pressure. Sound pressure level is usually measured in decibels (dB). The lower threshold of audibility is defined as 0 dB (20 micropascals), and the definition of the upper limit of audibility refers rather to the threshold of discomfort and then to hearing impairment, contusion, etc. This limit depends on how long we listen to the sound. The ear is capable of carrying short-term increase loudness up to 120 dB without consequences, but long-term exposure to sounds louder than 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 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 depressive states. Ultrasounds can cause astheno-vegetative syndromes, etc.
The audible part of the sound range is divided into low-frequency sounds - up to 500 hertz, mid-frequency - 500-10,000 hertz and high-frequency - over 10,000 hertz.

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

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

The auricle, external auditory canal, tympanic membrane, auditory ossicles, annular ligament of the oval window, membrane of the round window (secondary tympanic membrane), labyrinthine fluid (perilymph), and the main membrane take part in the conduction of sound vibrations.

In humans, the role of the auricle is relatively small. In animals that have the ability to move their ears, the pinnae help determine the direction of the source of sound. In humans, the auricle, like a megaphone, only collects sound waves. However, in this respect its role is insignificant. Therefore, when a person listens to quiet sounds, he puts his palm to his ear, due to which the surface of the auricle significantly increases.

Sound waves, having penetrated the ear canal, set the eardrum into friendly vibration, which transmits sound vibrations through the chain of auditory ossicles to oval window and then the perilymph of the inner ear.

The eardrum responds not only to those sounds whose number of vibrations coincides with its own tone (800-1000 Hz), but also to any sound. This resonance is called universal, in contrast to acute resonance, when a secondary sounding body (for example, a piano string) responds to only one specific tone.

The eardrum and auditory ossicles do not simply transmit sound vibrations entering the external auditory canal, but transform them, that is, they transform air vibrations with large amplitude and low pressure into vibrations of the labyrinth fluid with low amplitude and high pressure.

This transformation is achieved due to the following conditions: 1) the surface of the tympanic membrane is 15-20 times larger than the area of ​​the oval window; 2) the malleus and incus form an unequal lever, so that the excursions made by the foot plate of the stapes are approximately one and a half times less than the excursions of the malleus handle.

The overall effect of the transformative effect of the eardrum and the lever system of the auditory ossicles is expressed in an increase in sound intensity by 25-30 dB. Violation of this mechanism in case of damage to the eardrum and diseases of the middle ear leads to a corresponding decrease in hearing, i.e., by 25-30 dB.

For the normal functioning of the eardrum and the chain of auditory ossicles, it is necessary that the air pressure on both sides of the eardrum, i.e. in the external auditory canal and in the tympanic cavity, be the same.

This pressure equalization occurs due to the ventilation function of the auditory tube, which connects the tympanic cavity to the nasopharynx. With each swallowing movement, air from the nasopharynx enters the tympanic cavity, and thus the air pressure in the tympanic cavity is always maintained at atmospheric level, i.e. at the same level as in the external auditory canal.

The sound-conducting apparatus also includes the muscles of the middle ear, which perform the following functions: 1) maintaining the normal tone of the eardrum and the chain of auditory ossicles; 2) protection of the inner ear from excessive sound stimulation; 3) accommodation, i.e. adaptation of the sound-conducting apparatus to sounds of varying strength and height.

When the muscle that stretches the tympanic membrane contracts, auditory sensitivity increases, which gives reason to consider this muscle “alert.” The stapedius muscle plays the opposite role - when it contracts, it limits the movements of the stirrup and thereby, as it were, muffles sounds that are too strong.

The mechanism described above for transmitting sound vibrations from the external environment to the inner ear through the external auditory canal, eardrum and chain of auditory ossicles is airborne sound conduction. But sound can be delivered to the inner ear bypassing a significant part of this path, namely directly through the bones of the skull - bone sound conduction. Under the influence of fluctuations in the external environment, oscillatory movements of the bones of the skull, including the bony labyrinth, occur. These1 oscillatory movements are transmitted to the fluid of the labyrinth (perilymph). The same transmission occurs when a sounding body, for example the leg of a tuning fork, comes into direct contact with the bones of the skull, as well as under the influence of high-frequency sounds with a small vibration amplitude.

The presence of bone conduction of sound vibrations can be verified through simple experiments: 1) when both ears are tightly plugged with fingers, i.e., when the access of air vibrations through the external auditory canals is completely stopped, the perception of sounds deteriorates significantly, but still occurs; 2) if the leg of the sounding tuning fork is placed against the crown of the head or the mastoid process, then the sound of the tuning fork will be clearly audible even with the ears plugged.

Bone sound conduction is of particular importance in ear pathology. Thanks to this mechanism, the perception of sounds is ensured, although in a sharply weakened form, in cases where the transmission of sound vibrations through the outer and middle ear completely stops. Bone sound conduction is carried out, in particular, in case of complete blockage of the external auditory canal (for example, with cerumen), as well as in diseases that lead to immobility of the chain of auditory ossicles (for example, with otosclerosis).

As already mentioned, vibrations of the tympanic membrane are transmitted through the chain of ossicles to the oval window and cause movements of the perilymph, which spread along the scala vestibule to the scala tympani. These fluid movements are possible due to the presence of the round window membrane (secondary tympanic membrane), which, with each inward movement of the stapes plate and the corresponding push of the perilymph, protrudes towards the tympanic cavity. As a result of movements of the perilymph, vibrations of the main membrane and the organ of Corti located on it occur.

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 outer ear canal and the tympanic cavity is the tympanic membrane (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 the upper 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. Included 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 picked up by the auricle, sent to the external auditory canal, and cause vibrations in 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 position of the head 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 the third neurons of the auditory pathway are 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 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 cranial nuclei, providing regulation 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.

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).

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 under the influence of sound.

4. The malleus with its handle is attached to the center of the eardrum with the help of ligaments, and its head is connected to the incus (5), which, in turn, is attached to the stapes (6).

Tiny muscles help transmit sound by regulating the movement of these ossicles.

7. The Eustachian (or auditory) tube connects the middle ear to the nasopharynx. When the ambient air pressure changes, the pressure on both sides of the eardrum is equalized through the auditory tube.

8. Vestibular system. The vestibular system in our ear is part of the body's balance system. Sensory cells provide information about the position and movement of our head.

9. The cochlea is the organ of hearing directly connected to the auditory nerve. The name of the snail is determined by its spirally convoluted shape. This is a bone canal that forms two and a half turns of a spiral and is filled with fluid. The anatomy of the cochlea is very complex, and some of its functions are still unexplored.

The organ of Corti consists of a number of sensory, hair-bearing cells (12) that cover the basilar membrane (13). Sound waves are picked up by hair cells and converted into electrical impulses. These electrical impulses are then transmitted along the auditory nerve (11) to the brain. The auditory nerve consists of thousands of tiny nerve fibers. Each fiber starts from a specific part of the cochlea and transmits a specific sound frequency. Low-frequency sounds are transmitted through fibers emanating from the apex of the cochlea (14), and high-frequency sounds are transmitted through fibers connected to its base. Thus, the function of the inner ear is to convert mechanical vibrations into electrical ones, since the brain can only perceive electrical signals.

Outer ear is a sound-collecting device. The external auditory canal conducts sound vibrations to the eardrum. The eardrum, which separates the outer ear from the tympanic cavity, or middle ear, is a thin (0.1 mm) partition shaped like an inward funnel. The membrane vibrates 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 malleus, 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.

During strong sounds, special muscles reduce the mobility of the eardrum and auditory ossicles, adapting the hearing aid to such changes in the stimulus and protecting the inner ear from destruction.

Thanks to the connection of the air cavity of the middle ear with the cavity of the nasopharynx through the auditory tube, it becomes possible to equalize the pressure on both sides of the eardrum, which prevents its rupture during significant changes in pressure in the external environment - when diving under water, climbing to a height, shooting, etc. This is the barofunction of the ear .

There are two muscles in the middle ear: the tensor tympani and the stapedius. The first of them, contracting, increases the tension of the eardrum and thereby limits the amplitude of its vibrations during strong sounds, and the second fixes the stapes and thereby limits its movements. The reflex contraction of these muscles occurs 10 ms after the onset of a strong sound and depends on its amplitude. This automatically protects the inner ear from overload. For instantaneous strong irritations (impacts, explosions, etc.) this defense mechanism does not have time to work, which can lead to hearing impairment (for example, among bombers and artillerymen).

Inner ear is a sound-perceiving apparatus. It is located in the pyramid of the temporal bone and contains the cochlea, which in humans forms 2.5 spiral turns. The cochlear canal is divided by two partitions, the main membrane and the vestibular membrane into 3 narrow passages: upper (scala vestibular), middle (membranous canal) and lower (scala tympani). At the top of the cochlea there is a hole 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 arise, which are transmitted to the membrane of the round window. Another way of delivering sounds to the cochlea is fabric or bone conduction . In this case, the sound directly acts on the surface of the skull, causing it to vibrate. Bone pathway for sound transmission becomes of great importance if a vibrating object (for example, the stem of a tuning fork) comes into contact with the skull, as well as in diseases of the middle ear system, when the transmission of sounds through the chain of auditory ossicles is disrupted. In addition to the air path for conducting sound waves, there is a tissue, or bone, path. Under the influence of air sound vibrations, as well as when vibrators (for example, a bone telephone or a bone tuning fork) come into contact with the integument of the head, the bones of the skull begin to vibrate (the bone labyrinth also begins to vibrate) . Based on the latest data (Bekesy and others), it can be assumed that sounds propagating along the bones of the skull only excite the organ of Corti if, similar to air waves, they cause arching of a certain section of the main membrane. The ability of the skull bones to conduct sound explains why to the person himself his voice, recorded on tape, seems 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 the neurons of the auditory system to evaluate interaural (interaural) differences in the time of sound arrival on the right and left ear and sound intensity in each ear. If the sound source is located away from the midline of the head, the sound wave arrives at one ear slightly earlier and has greater strength than at the other ear. Assessing the distance of a sound source from the body is associated with a weakening of the sound and a change in its timbre.

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

There are 2 ways to conduct sound:

Based on the ability of a sound wave to propagate in solids. The bones of the skull conduct sound well. But the significance of this path for healthy person not great. But if air route is broken, then this path cannot be replaced. With the help of a sound apparatus, receptor irritation is achieved bypassing the air threshold.

2) Air

In this path, sound passes through:

· Auricle – external auditory canal – tympanic membrane – auditory ossicles – oval window – cochlea – fluid canals – nervous apparatus – round window.

Peripheral department analyzer. Represented by the organ of hearing – the ear. Highlight:

External ear (pinna, external auditory canal.

· Ears are a speaker and contribute to the concentration of sounds emanating from different parts of space in the direction of the external auditory canal.

· Restrict flow sound signals, coming from the rear.

· Execute protective function, protect the eardrum from thermal and mechanical influences. Provide temperature constant and humidity in this area.

The boundary between the outer and middle parts of the ear is the eardrum.

It has the shape of a cone with the apex directed into the middle ear cavity.

Functions:

· Provides transmission of vibrations to the middle ear, through the system of auditory ossicles.

Middle ear. Represented by the tympanic cavity and the ossicular hearing system

Functions:

· Conductive – conduction of sound. The malleus, incus and stapes form a lever that increases the pressure applied to the eardrum by 20 times.

· Protective, providing 2 muscles

1) Muscle that stretches the tympanic membrane

2) The stapedalis muscle, when contracted, fixes the stapes, limiting its movement

The function of these muscles is that, by contracting, they reduce the amplitude of vibrations of the eardrum and ossicles and thereby reduce the coefficient of sound pressure transmission to the inner ear. The cut occurs at sounds above 90 dB, but the cut has a latency period of 10 milliseconds that is too long.

When exposed to immediate strong stimuli, this mechanism does not work. When exposed to prolonged sounds, it has important role. Contraction of the stipendial muscle is observed during the action of a new stimulus, yawning, swallowing and speech activity.

The middle ear is connected to the back of the pharynx by a narrow canal called the eustachian tube. The function is to balance the pressure in the middle ear and the external environment.

Inner ear. Organ of hearing. Located in the cochlea, spirally twisted in shape. The cochlea is divided into three channels:

In the middle of the canal on the basilar membrane is the Gordian organ. Gordian organ - system cross fibers, the main membrane and sensitive striatal cells located on this membrane. Vibrations of the fibers, the main membrane, are transmitted to the hair cells, in which contact with the tectorial membrane overhanging them causes a receptor potential. Nerve impulses generated by hair cells are transmitted along the cochlear nerve to higher centers sound analyses.

The number of receptors tuned to a certain frequency changes.

Auditory pathways.

along the axon nerve cells spiral ganglion approaching receptor cells is transmitted to the auditory center of the medulla oblongata. Cochliary nuclei. After switching on the cells of the cochliary nuclei, electrical impulses enter the nuclei of the superior olive, here the first crossover is noted auditory pathways: less fiber remains on the sides auditory receptor, most of it goes to the opposite side. Next, the information passes through the medial geniculate. body and is transmitted to the superior temporal gyrus. Where the auditory sensation is formed.

Bilural hearing. Provides localization of the stimulus due to the non-simultaneous propagation of the sound wave to each ear.

Interaction with other organs and systems.

Somatic – sentinel reflex Visceral

taste system, is a chemoreceptive system that analyzes chemical stimuli operating at the taste level.

Taste- this is a sensation that occurs as a result of the influence of a substance on the receptors. Located on the surface of the tongue and mucous membrane oral cavity. Taste is a contact type of sensitivity. Taste is a multimodal sensory experience. There are 4 tastes of sensitivity: sweet, sour, salty, bitter. Tip tongue - sweet, the root is bitter, the side surfaces are sour and salty.

The taste threshold depends on the concentration of the substance. The lowest is bitter, sweet is higher, the threshold for sour and salty is close to sweet. The intensity depends on the size of the tongue surface and temperature. With prolonged exposure to receptors, adaptation occurs and the threshold increases significantly.

Prescription machine.

Taste buds are located in the form of complexes, taste buds (about 2000). Consisting of 40-60 receptor cells. Each taste bud contains about 50 nerve fibers. Taste buds are located in taste buds having a different structure and located on the tongue. There are 3 types of papillae:

1) Mushroom-shaped. Located on all surfaces of the tongue

2) Gutters. Back, root

3) Leaf-shaped. Along the posterior edges of the tongue.

The taste bud excites due to the interaction of stimuli with receptor molecules located on the stimulus membrane.

Olfactory system.

Performs the perception and analysis of chemical stimuli located in the external environment and acting on the olfactory organs.

Smell is the perception by organisms of certain properties of substances using the olfactory organs.

Classification of odors.

There are 7 main smells:

1) Camphoraceae-eucalyptus

2) Essential - pear

3) Musk-musk

4) Floral – rose

5) Putrid - rotten eggs

6) Caustic – vinegar

7) Mint – mint

The receptor apparatus is represented by the olfactory epithelium. Olfactory receptors have cytoplasmic outgrowths - cilia. This allows you to increase the area of ​​smell by 100-150 times. The molecules of the odorous substance coincide with the ultramicroscopic structure of the olfactory cells, like a key and a lock. This interaction leads to changes in membrane permeability, its defoliation and development nerve impulse. The axons united in a bundle go to the olfactory bulb from there, as part of the olfactory tract, to many brain structures, the nuclei of the third brain, the limbic system, the hypothalamus.

Vestibular analyzer

Sensory system, which perceives, transmits and analyzes information about the spatial orientation of the body and ensures the implementation of tonic, complexly coordinated reflexes.