Scheme of the structure of the peripheral part of the auditory analyzer. How the auditory analyzer works

14.3. auditory analyzer

The outer ear consists of the auricle and the external auditory meatus.

The basis of the auricle is elastic cartilage, supplemented by a skin fold - a lobe filled with adipose tissue. The ear rakbvina in a newborn is flattened, its cartilage is soft, the skin is thin, the lobe is small. The auricle grows most rapidly during the first two years and after 10 years. It grows faster in length than in width. The free edge of the shell is wrapped inward in the form of a curl, and an antihelix rises from its bottom. Medial to the latter is the shell cavity, in the depth of which there is an opening of the external auditory meatus. A tragus is located in front of it, and an anti-tragus is behind it.

The external auditory meatus is 24 mm long and terminates in the tympanic membrane. The first third of the auditory meatus is a cartilaginous continuation of the shell, the remaining two thirds are bony and are located in the pyramid of the temporal bone. External auditory canal

in a newborn, it is narrow and long (15 mm), steeply curved, has a narrowing, its medial and lateral sections are expanded. The walls of the external auditory meatus are cartilaginous, with the exception of the tympanic ring. The length of the ear canal in a child of 1 year old is 20 mm, and 5 years old - 22 mm. The ear canal is lined with thin-fibre skin and modified sweat glands that secrete earwax. All this protects the eardrum from the adverse effects of the external environment. The eardrum separates the outer ear from the middle ear. It consists of collagen fibers, covered on the outside by the epidermis, and inside - by the mucous membrane. The tympanic membrane in a newborn is well developed. Its height is 9 mm, width - 8 mm, as in an adult, and forms an angle of 35-40 °.

The middle ear consists of the tympanic cavity, the auditory ossicles and the auditory tube.

On the front wall of the tympanic cavity there is an opening of the auditory tube, through which it is filled with air. On the posterior wall of the cavity, the cells of the mastoid process open, and on the medial wall, the vestibule window and the cochlear window are located, which lead to the inner ear. The tympanic cavity in a newborn is the same size as in an adult. The mucous membrane is thickened, and therefore the tympanic cavity is filled with fluid. With the onset of breathing, it enters through the auditory tube into the pharynx and is swallowed. The walls of the tympanic cavity are thin, especially the upper one. The back wall has a wide opening leading to the mastoid cavity. Mastoid cells in infants are absent due to poor development of the mastoid process. The cochlear window is covered by the secondary tympanic membrane.

The middle ear contains three auditory ossicles: the malleus, anvil, and stirrup. The malleus is connected on one side to the eardrum, and on the other - to the body of the anvil. The long process of the latter articulates with the head of the stirrup. The base of the stirrup is adjacent to the window of the vestibule. The auditory ossicles in a newborn are similar in size to those in an adult. All three bones connect the eardrum to the inner ear.

The auditory tube is a long (3.5 cm) and narrow (2 mm) cartilaginous canal that passes into the bone canal from the side of the pyramid. The tube serves to equalize air pressure on the eardrum. The opening of the tube in the pharynx is in a collapsed state and air enters the tympanic cavity only when swallowing or yawning.

The auditory tube in a newborn is straight, wide and short, 17-18 mm long. During the first year of life, it grows slowly (20 mm), in the second year it grows faster (30 mm). At 5 years old, its length is 35 mm, in an adult - 35-38 mm. The lumen of the auditory tube narrows from 2.5 mm at 6 months to 2 mm at 2 years and 1-2 mm at 6 years.

The inner ear, or labyrinth, has double walls: the membranous labyrinth is inserted into the bone one. Between them is a transparent liquid - perilymph, and inside the membranous - endolymph.

The bony labyrinth consists of the vestibule, cochlea, and three semicircular canals. The vestibule is an oval cavity connected to the tympanic cavity by a septum with two windows: oval (window of the vestibule) and round (window of the cochlea). The openings of the three semicircular canals and the spiral canal of the cochlea open into the vestibule. The structure of the semicircular canals will be considered in the description of the vestibular analyzer. The bony cochlea is a spiral canal that has two and a half turns around the cochlear shaft. A bone spiral plate departs from the rod, not reaching the outer wall of the canal. From the free end of the spiral plate to the opposite wall of the cochlea, two membranes are stretched - spiral and vestibular, which limit the cochlear duct. The cochlear duct divides the cochlea into two parts, or scalas. The upper part, or scala vestibuli, starts from the oval window of the vestibule and goes to the top of the cochlea, where it communicates through a small opening with the lower canal, or scala tympani. It extends from the top of the cochlea to the round window of the cochlea. The vestibular and tympanic scalas are filled with perilymph, and the lumen of the cochlear duct is filled with endolymph. The inner ear of a newborn is well developed, its dimensions are close to those of an adult. The bony walls of the semicircular canals are thin, gradually thickening due to ossification in the pyramid of the temporal bone.

On the spiral membrane lies a spiral organ, consisting of supporting and receptor cells. On the supporting cells of a cylindrical shape are receptor hair cells, which have outgrowths on their upper part, represented by large microvilli (stereocilia). Hair cells are external, arranged in three rows, and internal, forming only one row. Between the outer and inner hair cells lies the tunnel of Corti, lined with columnar cells.

The cilia of the outer and inner hair cells are in contact with the integumentary (tectorial) membrane. This membrane is a homogeneous jelly-like mass attached to epithelial cells. The spiral membrane is not the same in width: in humans, near the oval window, its width is 0.04 mm, and then towards the top of the cochlea, gradually expanding, it reaches 0.5 mm at the end. In the basal part of the spiral organ there are receptor cells that perceive higher frequencies, and in the apical part (at the top of the cochlea) there are cells that perceive only low frequencies.

The basal parts of the receptor cells come into contact with the nerve fibers that pass through the basement membrane and then exit into the canal of the spiral lamina. Then they go to the neurons of the spiral ganglion, which lies in the bony cochlea, where the conductive section of the auditory analyzer begins. The axons of the neurons of the spiral ganglion form the fibers of the auditory nerve, which enters the brain between the lower cerebellar peduncles and the pons and goes to the pons tegmentum, where the first crossing of the fibers takes place and a lateral loop is formed. Some of its fibers terminate on the cells of the inferior colliculus, where the primary auditory center is located. Other fibers of the lateral loop in the handle of the inferior colliculus approach the medial geniculate body. The processes of the cells of the latter form auditory radiance, ending in the cortex of the superior temporal gyrus (cortical section of the auditory analyzer).

Mechanism of sound production

As a result of the occurrence of electrical potentials, the fibers of the auditory nerve are excited, which are characterized by spontaneous activity even in silence (100 pulses / s). With sound, the frequency of impulses in the fibers increases during the entire time of the stimulus. For each nerve fiber, there is an optimal sound frequency that gives the highest discharge frequency and the lowest response threshold. This optimal frequency is determined by the place on the main membrane where the receptors associated with this fiber are located. Thus, the fibers of the auditory nerve are characterized by frequency selectivity due to the excitation of different cells of the spiral organ. If the spiral organ is damaged, high tones drop out at the base, low tones at the top. The destruction of the middle curl leads to the loss of tones of the middle frequency of the range.

There are two mechanisms for pitch discrimination: spatial and temporal coding. Spatial coding is based on the unequal arrangement of excited receptor cells on the main membrane. At low and medium tones, temporal coding is also carried out. Information in this case is transmitted to certain groups of fibers of the auditory nerve, the frequency corresponds to the frequency of sound vibrations perceived by the cochlea.

All auditory neurons are characterized by the presence of frequency-threshold indicators. These indicators reflect the dependence of the threshold sound required to excite the cell on its frequency. On both sides of the optimal frequency, the response threshold of the neuron increases, i.e. the neuron is tuned to sounds of only a certain frequency.

All this confirmed the hypothesis of G. Helmholtz (1863) about the mechanism of distinguishing sounds in the organ of Corti by their pitch. According to this hypothesis, the transverse fibers of the main membrane are short in its narrow part - at the base of the cochlea and 3-4 times longer in its wide part - at the top. They are tuned like the strings of musical instruments. Vibration of individual groups of fibers causes irritation of the corresponding receptor cells in the corresponding sections of the main membrane. These assumptions of G. Helmholtz were confirmed and were partially modified and developed in the works of the American physiologist D. Bekeshi (1968).

The strength of the sound is encoded by the number of excited neurons. With weak stimuli, only a small number of the most sensitive neurons are involved in the reaction, and with increasing sound, more and more additional neurons are excited. This is due to the fact that the neurons of the auditory analyzer differ sharply from each other in terms of the excitation threshold. The threshold is different for internal and external cells (for internal cells it is much higher), therefore, depending on the strength of the sound, the ratio of the number of excited external and internal cells changes.

A person perceives sounds with a frequency of 16 to 20,000 Hz. This range corresponds to 10-11 octaves. The boundaries of hearing depend on age: the older the person, the more often he does not hear high tones. The difference in the frequency of sounds is characterized by the minimum difference in frequency of two sounds that a person catches. A person is able to notice a difference of 1-2 Hz.

Absolute auditory sensitivity is the minimum strength of a sound heard by a person in half of the cases of its sound. In the region from 1000 to 4000 Hz, human hearing has maximum sensitivity. Speech fields also lie in this zone. The upper limit of audibility occurs when an increase in the volume of a sound of a constant frequency causes an unpleasant feeling of pressure and pain in the ear. The unit of sound volume is Bel. In everyday life, decibels are usually used as a unit of loudness, i.e. 0.1 bela. The maximum volume level when sound causes pain is 130-140 dB above the threshold of hearing.

If one or another sound acts on the ear for a long time, then the hearing sensitivity decreases, i.e. adaptation occurs. The mechanism of adaptation is associated with contraction of the muscles leading to the tympanic membrane and stirrup (when they contract, the intensity of sound energy transmitted to the cochlea changes), and with the downward influence of the reticular formation of the midbrain.

The auditory analyzer has two symmetrical halves (binaural hearing), i.e. a person is characterized by spatial hearing - the ability to determine the position of a sound source in space. The acuteness of such hearing is great. A person can determine the location of the sound source with an accuracy of 1 °. This is because if the sound source is away from the midline of the head, the sound wave arrives at one ear earlier and with more force than the other. In addition, at the level of the posterior colliculi of the quadrigemina, neurons were found that respond only to a certain direction of movement of the sound source in space.

Hearing in ontogeny

Despite the early development of the auditory analyzer, the organ of hearing in a newborn is not yet fully formed. He has relative deafness, which is associated with structural features of the ear. The middle ear cavity in newborns is filled with amniotic fluid, which makes it difficult for the auditory ossicles to vibrate. The amniotic fluid gradually dissolves, and air enters the ear cavity from the nasopharynx through the Eustachian tube.

The newborn reacts to loud sounds with a start, a cessation of crying, a change in breathing. The hearing in children becomes quite distinct by the end of the 2nd - the beginning of the 3rd month. At the 2nd month of life, the child differentiates qualitatively different sounds, at 3-4 months he distinguishes pitch in the range from 1 to 4 octaves, at 4-5 months the sounds become conditioned stimuli, although conditioned food and defensive reflexes to sound stimuli are already developed from 3 -5 weeks of age. By the age of 1-2, children differentiate sounds, the difference between which is 1 tone, and by 4 years - even 3/4 and 1/2 tones.

Hearing acuity is defined as the smallest amount of sound that can cause a sound sensation (hearing threshold). In an adult, the hearing threshold lies in the range of 10-12 dB, in children 6-9 years old - 17-24 dB, 10-12 years old - 14-19 dB. The greatest sharpness of sound is achieved by the middle and senior school age. Children perceive low tones better than high ones. In the development of hearing in children, communication with adults is of great importance. Develops hearing in children listening to music, learning to play musical instruments.

Introduction

Conclusion

Bibliography

Introduction

The society in which we live is an information society, where the main factor of production is knowledge, the main product of production is services, and the characteristic features of society are computerization, as well as a sharp increase in creativity in labor. The role of relations with other countries is growing, the process of globalization is taking place in all spheres of society.

A key role in communication between states is played by professions related to foreign languages, linguistics, and social sciences. There is a growing need to study speech recognition systems for automated translation, which will increase labor productivity in the areas of the economy related to intercultural communication. Therefore, it is important to study the physiology and mechanisms of functioning of the auditory analyzer as a means of perceiving and transmitting speech to the corresponding part of the brain for subsequent processing and synthesis of new speech units.

The auditory analyzer is a combination of mechanical, receptor and nervous structures, the activity of which ensures the perception of sound vibrations by humans and animals. From an anatomical point of view, the auditory system can be divided into the outer, middle and inner ear, the auditory nerve and the central auditory pathways. From the point of view of the processes that ultimately lead to the perception of hearing, the auditory system is divided into sound-conducting and sound-perceiving.

Under different environmental conditions, under the influence of many factors, the sensitivity of the auditory analyzer may change. To study these factors, there are various methods of studying hearing.

auditory analyzer physiology sensitivity

1. The importance of studying human analyzers from the point of view of modern information technologies

Already several decades ago, people made attempts to create speech synthesis and recognition systems in modern information technologies. Of course, all these attempts began with the study of the anatomy and principles of the speech and auditory organs of a person, in the hope of modeling them using a computer and special electronic devices.

What are the features of the human auditory analyzer? The auditory analyzer captures the shape of a sound wave, the frequency spectrum of pure tones and noises, analyzes and synthesizes the frequency components of sound stimuli within certain limits, detects and identifies sounds in a wide range of intensity and frequencies. The auditory analyzer allows you to differentiate sound stimuli and determine the direction of the sound, as well as the remoteness of its source. The ears pick up vibrations in the air and convert them into electrical signals that are sent to the brain. As a result of processing by the human brain, these signals turn into images. The creation of such information processing algorithms for computer technology is a scientific task, the solution of which is necessary for the development of the most error-free speech recognition systems.

With the help of speech recognition programs, many users dictate the texts of documents. This possibility is relevant, for example, for doctors conducting an examination (during which their hands are usually busy) and at the same time recording its results. PC users can use speech recognition programs to enter commands, that is, the spoken word will be perceived by the system as a mouse click. The user commands: "Open file", "Send mail" or "New window", and the computer performs the appropriate action. This is especially true for people with disabilities - instead of a mouse and keyboard, they will be able to control the computer with their voice.

Studying the inner ear is helping researchers understand the mechanisms by which a person is able to recognize speech, although it is not so simple. Man "peeps" many inventions from nature, and such attempts are also being made by specialists in the field of speech synthesis and recognition.

2. Types of human analyzers and their brief description

Analyzers (from the Greek. analysis - decomposition, dismemberment) - a system of sensitive nerve formations that analyze and synthesize the phenomena of the external and internal environment of the body. The term was introduced into the neurological literature by I.P. Pavlov, according to whose ideas each analyzer consists of specific perceiving formations (receptors, sensory organs) that make up the peripheral section of the analyzer, the corresponding nerves that connect these receptors with different levels of the central nervous system (conductor part), and the brain end, represented in higher animals in the cortex of large hemispheres of the brain.

Depending on the receptor function, analyzers of the external and internal environment are distinguished. The first receptors are turned to the external environment and are adapted to analyze the phenomena occurring in the surrounding world. These analyzers include a visual analyzer, an auditory analyzer, a skin analyzer, an olfactory analyzer, and a taste analyzer. Analyzers of the internal environment are afferent nerve devices, the receptor apparatuses of which are located in the internal organs and are adapted to analyze what is happening in the body itself. These analyzers also include a motor analyzer (its receptor apparatus is represented by muscle spindles and Golgi receptors), which provides the possibility of precise control of the musculoskeletal system. An important role in the mechanisms of statokinetic coordination is also played by another internal analyzer - the vestibular one, which closely interacts with the movement analyzer. The human motor analyzer also includes a special department that ensures the transmission of signals from the receptors of the speech organs to the higher floors of the central nervous system. Due to the importance of this department in the activity of the human brain, it is sometimes considered as a "speech-motor analyzer".

The receptor apparatus of each analyzer is adapted to the transformation of a certain type of energy into nervous excitation. So, sound receptors selectively react to sound stimuli, light - to light, taste - to chemical, skin - to tactile-temperature, etc. The specialization of receptors provides an analysis of the phenomena of the external world into their individual elements already at the level of the peripheral section of the analyzer.

The biological role of analyzers is that they are specialized tracking systems that inform the body about all events occurring in the environment and inside it. From the huge stream of signals that continuously enter the brain through external and internal analyzers, that useful information is selected that turns out to be essential in the processes of self-regulation (maintaining an optimal, constant level of body functioning) and the active behavior of animals in the environment. Experiments show that the complex analytical and synthetic activity of the brain, determined by the factors of the external and internal environment, is carried out according to the polyanalyzer principle. This means that the entire complex neurodynamics of cortical processes, which form the integral activity of the brain, is made up of a complex interaction of analyzers. But that concerns another topic. Let's go directly to the auditory analyzer and consider it in more detail.

3. Auditory analyzer as a means of perceiving sound information by a person

3.1 Physiology of the auditory analyzer

The peripheral part of the auditory analyzer (auditory analyzer with an organ of balance - the ear (auris)) is a very complex sensory organ. The endings of his nerve are laid deep in the ear, thanks to which they are protected from the action of all kinds of extraneous stimuli, but at the same time they are easily accessible to sound stimuli. There are three types of receptors in the ear:

a) receptors that perceive sound vibrations (vibrations of air waves), which we perceive as sound;

b) receptors that enable us to determine the position of our body in space;

c) receptors that perceive changes in direction and speed of movement.

The ear is usually divided into three sections: the outer, middle and inner ear.

outer earconsists of the auricle and the external auditory canal. The auricle is built of elastic elastic cartilage, covered with a thin, inactive layer of skin. She is a collector of sound waves; in humans, it is motionless and does not play an important role, unlike animals; even with its complete absence, there is no noticeable hearing loss.

The external auditory meatus is a slightly curved canal about 2.5 cm long. This canal is lined with skin with fine hairs and contains special glands, similar to the large apocrine glands of the skin, which secrete earwax, which, together with hairs, prevents dust from clogging the outer ear. It consists of an outer section - a cartilaginous external auditory canal and an internal one - a bony auditory canal located in the temporal bone. Its inner end is closed by a thin elastic tympanic membrane, which is a continuation of the skin of the external auditory canal and separates it from the middle ear cavity. The outer ear in the organ of hearing plays only an auxiliary role, participating in the collection and conduction of sounds.

Middle ear, or the tympanic cavity (Fig. 1), is located inside the temporal bone between the external auditory canal, from which it is separated by the tympanic membrane, and the inner ear; it is a very small irregular cavity with a capacity of up to 0.75 ml, which communicates with the adnexal cavities - the cells of the mastoid process and with the pharyngeal cavity (see below).

Rice. 1. The organ of hearing in the context. 1 - geniculate node of the facial nerve; 2 - facial nerve; 3 - hammer; 4 - superior semicircular canal; 5 - posterior semicircular canal; 6 - anvil; 7 - the bone part of the external auditory canal; 8 - cartilaginous part of the external auditory canal; 9 - eardrum; 10 - bone part of the auditory tube; 11 - cartilaginous part of the auditory tube; 12 - large superficial stony nerve; 13 - the top of the pyramid.

On the medial wall of the tympanic cavity, facing the inner ear, there are two openings: the oval window of the vestibule and the round window of the cochlea; the first is covered with a stirrup plate. The tympanic cavity through a small (4 cm long) auditory (Eustachian) tube (tuba auditiva) communicates with the upper pharynx - the nasopharynx. The opening of the pipe opens on the side wall of the pharynx and in this way communicates with the outside air. Whenever the auditory tube opens (which happens with every swallowing movement), the air in the tympanic cavity is renewed. Thanks to it, the pressure on the tympanic membrane from the side of the tympanic cavity is always maintained at the level of the pressure of the outside air, and thus, the outside and inside of the tympanic membrane is subjected to the same atmospheric pressure.

This balancing of pressure on both sides of the tympanic membrane is very important, since normal fluctuations are possible only when the pressure of the outside air is equal to the pressure in the middle ear cavity. When there is a difference between the pressure of atmospheric air and the pressure of the tympanic cavity, hearing acuity is impaired. Thus, the auditory tube is, as it were, a kind of safety valve that equalizes the pressure in the middle ear.

The walls of the tympanic cavity and especially the auditory tube are lined with epithelium, and the mucous pipes are lined with ciliated epithelium; the vibration of its hairs is directed towards the pharynx.

The pharyngeal end of the auditory tube is rich in mucous glands and lymph nodes.

On the lateral side of the cavity is the tympanic membrane. The tympanic membrane (membrana tympani) (Fig. 2) perceives the sound vibrations of the air and transmits them to the sound-conducting system of the middle ear. It has the shape of a circle or ellipse with a diameter of 9 and 11 mm and consists of elastic connective tissue, the fibers of which are arranged radially on the outer surface, and circularly on the inner; its thickness is only 0.1 mm; it is stretched somewhat obliquely: from top to bottom and from back to front, slightly concave inward, since the mentioned muscle stretches the eardrum from the walls of the tympanic cavity to the handle of the malleus (it pulls the membrane inward). The chain of auditory ossicles serves to transmit air vibrations from the eardrum to the fluid that fills the inner ear. The tympanic membrane is not strongly stretched and does not emit its own tone, but transmits only the sound waves it receives. Due to the fact that the vibrations of the tympanic membrane decay very quickly, it is an excellent pressure transmitter and almost does not distort the shape of the sound wave. Outside, the tympanic membrane is covered with thinned skin, and from the surface facing the tympanic cavity, it is covered with a mucous membrane lined with squamous stratified epithelium.

Between the tympanic membrane and the oval window is a system of small auditory ossicles that transmit the vibrations of the tympanic membrane to the inner ear: the malleus (malleus), anvil (incus) and stirrup (stapes), interconnected by joints and ligaments, which are driven by two small muscles. The hammer is attached to the inner surface of the tympanic membrane with its handle, and the head is articulated with the anvil. The anvil, by one of its processes, is connected to the stirrup, which is located horizontally and with its wide base (plate) is inserted into the oval window, tightly adhering to its membrane.

Rice. 2. Tympanic membrane and auditory ossicles from the inside. 1 - head of the malleus; 2 - its upper ligament; 3 - cave of the tympanic cavity; 4 - anvil; 5 - a bunch of her; 6 - drum string; 7 - pyramidal elevation; 8 - stirrup; 9 - hammer handle; 10 - eardrum; 11 - Eustachian tube; 12 - a partition between the half-channels for the pipe and for the muscle; 13 - muscle straining the eardrum; 14 - anterior process of the malleus

The muscles of the tympanic cavity deserve great attention. One of them is m. tensor tympani - attached to the neck of the malleus. With its contraction, the articulation between the hammer and the anvil is fixed and the tension of the tympanic membrane increases, which occurs with strong sound vibrations. At the same time, the base of the stirrup is somewhat pressed into the oval window.

The second muscle is m. stapedius (the smallest of the striated muscles in the human body) - attached to the head of the stirrup. With the contraction of this muscle, the articulation between the anvil and the stirrup is pulled downward and limits the movement of the stirrup in the oval window.

Inner ear.The inner ear is represented by the most important and most complex part of the hearing aid, called the labyrinth. The labyrinth of the inner ear is located deep in the pyramid of the temporal bone, as if in a bone case between the middle ear and the internal auditory meatus. The size of the bony ear labyrinth along its long axis does not exceed 2 cm. It is separated from the middle ear by oval and round windows. The opening of the internal auditory meatus on the surface of the pyramid of the temporal bone, through which the auditory nerve exits the labyrinth, is closed by a thin bone plate with small holes for the fibers of the auditory nerve to exit the inner ear. Inside the bone labyrinth there is a closed connective tissue membranous labyrinth, exactly repeating the shape of the bone labyrinth, but somewhat smaller. The narrow space between the bony and membranous labyrinths is filled with a fluid similar in composition to lymph and called perilymph. The entire internal cavity of the membranous labyrinth is also filled with a fluid called endolymph. The membranous labyrinth, but in many places, is connected to the walls of the bony labyrinth by dense cords running through the perilymphatic space. Due to this arrangement, the membranous labyrinth is suspended inside the bony labyrinth, just as the brain is suspended (inside the skull on its meninges.

The labyrinth (Fig. 3 and 4) consists of three sections: the vestibule of the labyrinth, the semicircular canals and the cochlea.

Rice. 3. Scheme of the relationship of the membranous labyrinth to the bone. 1 - duct connecting the uterus with the sac; 2 - upper membranous ampulla; 3 - endolymphatic duct; 4 - endolymphatic sac; 5 - perilymphatic space; 6 - pyramid of the temporal bone: 7 - apex of the membranous cochlear duct; 8 - communication between both ladders (helicotrema); 9 - cochlear membranous passage; 10 - staircase of the vestibule; 11 - drum ladder; 12 - bag; 13 - connecting stroke; 14 - perilymphatic duct; 15 - round window of the snail; 16 - oval window of the vestibule; 17 - tympanic cavity; 18 - blind end of the cochlear passage; 19 - posterior membranous ampulla; 20 - uterus; 21 - semicircular canal; 22 - upper semicircular course

Rice. 4. Cross section through the course of the cochlea. 1 - staircase of the vestibule; 2 - Reissner's membrane; 3 - integumentary membrane; 4 - cochlear canal, in which the organ of Corti is located (between the integumentary and main membranes); 5 and 16 - auditory cells with cilia; 6 - supporting cells; 7 - spiral ligament; 8 and 14 - cochlear bone tissue; 9 - supporting cell; 10 and 15 - special supporting cells (the so-called Corti cells - pillars); 11 - drum stairs; 12 - main membrane; 13 - nerve cells of the spiral cochlear ganglion

The membranous vestibule (vestibulum) is a small oval cavity that occupies the middle part of the labyrinth and consists of two bubble sacs connected by a narrow tubule; one of them - the back, the so-called uterus (utriculus), communicates with the membranous semicircular canals with five holes, and the anterior sac (sacculus) - with the membranous cochlea. Each of the sacs of the vestibular apparatus is filled with endolymph. The walls of the sacs are lined with squamous epithelium, with the exception of one area - the so-called macula, where there is a cylindrical epithelium containing supporting and hair cells that carry thin processes on their surface facing the cavity of the sac. In higher animals, there are small crystals of lime (otoliths) glued into one lump together with hairs of neuroepithelial cells in which the nerve fibers of the vestibular nerve (ramus vestibularis - a branch of the auditory nerve) terminate.

Behind the vestibule are three mutually perpendicular semicircular canals (canales semicirculares) - one in the horizontal plane and two in the vertical. The semicircular canals are very narrow tubes filled with endolymph. Each of the channels forms an extension at one of its ends - an ampulla, where the ends of the vestibular nerve are located, distributed in the cells of the sensitive epithelium, concentrated in the so-called auditory scallop (crista acustica). The cells of the sensitive epithelium of the auditory crest are very similar to those found in the speck - on the surface facing the cavity of the ampoule, they carry hairs that are glued together and form a kind of brush (cupula). The free surface of the brush reaches the opposite (upper) wall of the canal, leaving an insignificant lumen of its cavity free, preventing the movement of the endolymph.

In front of the vestibule is the cochlea (cochlea), which is a membranous spirally convoluted canal, also located inside the bone. Cochlear spiral in human makes 2 3/4turnover around the central bone axis and ends blind. The bony axis of the cochlea with its apex faces the middle ear, and with its base closes the internal auditory meatus.

In the cavity of the spiral canal of the cochlea, along its entire length, a spiral bone plate departs and protrudes from the bone axis - a septum that divides the spiral cavity of the cochlea into two passages: the upper one, which communicates with the vestibule of the labyrinth, the so-called vestibule ladder (scala vestibuli), and the lower one, resting at one end into the membrane of the round window of the tympanic cavity and therefore called the scala tympani (scala tympani). These passages are called stairs because, curling in a spiral, they resemble a staircase with an obliquely rising strip, but without steps. At the end of the cochlea, both passages are connected by a hole about 0.03 mm in diameter.

This longitudinal bone plate that blocks the cavity of the cochlea, extending from the concave wall, does not reach the opposite side, and its continuation is a connective tissue membranous spiral plate, called the main membrane, or the main membrane (membrana basilaris), which already closely adjoins the convex opposite wall along the entire length of the common cavity of the cochlea.

Another membrane (Reisner's) departs from the edge of the bone plate at an angle above the main one, which limits a small average course between the first two moves (ladders). This move is called the cochlear canal (ductus cochlearis) and communicates with the vestibule sac; he is the organ of hearing in the proper sense of the word. The canal of the cochlea in a transverse section has the shape of a triangle and, in turn, is divided (but not completely) into two floors by a third membrane - the integumentary (membrana tectoria), which apparently plays a large role in the process of perception of sensations. In the lower floor of this last canal, on the main membrane in the form of a protrusion of the neuroepithelium, there is a very complex device that actually perceives the auditory analyzer - a spiral (Corti) organ (organon spirale Cortii) (Fig. 5), washed along with the main membrane by the intralabyrinth fluid and playing with respect to to hearing the same role as the retina in relation to vision.

Rice. 5. Microscopic structure of Corti's organ. 1 - main membrane; 2 - cover membrane; 3 - auditory cells; 4 - auditory ganglion cells

The spiral organ consists of numerous diverse supporting and epithelial cells located on the main membrane. The elongated cells are arranged in two rows and are called the pillars of Korti. The cells of both rows are somewhat inclined towards each other and form up to 4000 arcs of Corti throughout the cochlea. In this case, a so-called internal tunnel filled with intercellular substance is formed in the cochlear canal. On the inner surface of the columns of Corti there are a number of cylindrical epithelial cells, on the free surface of which there are 15-20 hairs - these are sensitive, perceiving, so-called hair cells. Thin and long fibers - auditory hairs, gluing together, form delicate brushes on each such cell. Supporting Deiters cells adjoin the outer side of these auditory cells. Thus, the hair cells are anchored to the basal membrane. Thin, non-fleshy nerve fibers approach them and form an extremely delicate fibrillar network in them. The auditory nerve (its branch - ramus cochlearis) penetrates into the middle of the cochlea and goes along its axis, giving off numerous branches. Here, each pulpy nerve fiber loses its myelin and passes into a nerve cell, which, like spiral ganglion cells, has a connective tissue sheath and glial sheath cells. The total sum of these nerve cells as a whole forms a spiral ganglion (ganglion spirale), which occupies the entire periphery of the cochlear axis. From this nerve ganglion, nerve fibers are already directed to the perceiving apparatus - the spiral organ.

The very same main membrane, on which the spiral organ is located, consists of the thinnest, dense and tightly stretched fibers, ("strings") (about 30,000), which, starting from the base of the cochlea (near the oval window), gradually lengthen to its upper curl, going from 50 to 500 ?(more precisely, from 0.04125 to 0.495 mm), i.e. short near the oval window, they become progressively longer towards the top of the cochlea, increasing about 10-12 times. The length of the main membrane from the base to the top of the cochlea is approximately 33.5 mm.

Helmholtz, who created the theory of hearing at the end of the last century, compared the main membrane of the cochlea with its fibers of different lengths with a musical instrument - a harp, only in this living harp a huge number of "strings" are stretched.

The perceiving apparatus of auditory stimuli is the spiral (Corti) organ of the cochlea. The vestibule and semicircular canals play the role of organs of balance. True, the perception of the position and movement of the body in space depends on the joint function of many sense organs: vision, touch, muscle feeling, etc., i.e. the reflex activity necessary to maintain balance is provided by impulses in various organs. But the main role in this belongs to the vestibule and semicircular canals.

3.2 Sensitivity of the auditory analyzer

The human ear perceives air vibrations from 16 to 20,000 Hz as sound. The upper limit of perceived sounds depends on age: the older the person, the lower it is; often old people do not hear high tones, for example, the sound made by a cricket. In many animals the upper limit lies higher; in dogs, for example, it is possible to form a whole series of conditioned reflexes to sounds inaudible to humans.

With fluctuations up to 300 Hz and above 3000 Hz, the sensitivity decreases sharply: for example, at 20 Hz, and also at 20,000 Hz. With age, the sensitivity of the auditory analyzer, as a rule, decreases significantly, but mainly to high-frequency sounds, while to low ones (up to 1000 oscillations per second) it remains almost unchanged until old age.

This means that in order to improve the quality of speech recognition, computer systems can exclude from the analysis frequencies lying outside the range of 300-3000 Hz or even outside the range of 300-2400 Hz.

In conditions of complete silence, the sensitivity of hearing increases. If, however, a tone of a certain height and constant intensity begins to sound, then, as a result of adaptation to it, the sensation of loudness decreases first quickly, and then more and more slowly. However, although to a lesser extent, the sensitivity to sounds that are more or less close in frequency to the sounding tone decreases. However, adaptation usually does not cover the entire range of perceived sounds. When the sound stops, due to adaptation to silence, the previous level of sensitivity is restored in 10-15 seconds.

In part, adaptation depends on the peripheral part of the analyzer, namely, on changes in both the amplifying function of the sound apparatus and the excitability of the hair cells of the organ of Corti. The central section of the analyzer also takes part in the phenomena of adaptation, as evidenced by the fact that when sound is applied to only one ear, shifts in sensitivity are observed in both ears.

The sensitivity also changes with the simultaneous action of two tones of different heights. In the latter case, a weak sound is drowned out by a stronger one, mainly because the focus of excitation, which arises in the cortex under the influence of a strong sound, lowers the excitability of other parts of the cortical section of the same analyzer due to negative induction.

Prolonged exposure to strong sounds can cause inhibition of cortical cells. As a result, the sensitivity of the auditory analyzer drops sharply. This state persists for some time after the irritation has ceased.

Conclusion

The complex structure of the auditory analyzer system is due to the multistage algorithm for signal transmission to the temporal region of the brain. The outer and middle ear transmit sound vibrations to the cochlea located in the inner ear. Sensory hairs located in the cochlea convert vibrations into electrical signals that travel along the nerves to the auditory area of the brain.

When considering the issue of the functioning of the auditory analyzer for the further application of knowledge when creating speech recognition programs, one should also take into account the sensitivity limits of the hearing organ. The frequency range of sound vibrations perceived by a person is 16-20,000 Hz. However, the frequency range of speech is already 300-4000 Hz. Speech remains intelligible with further narrowing of the frequency range to 300-2400 Hz. This fact can be used in speech recognition systems to reduce the effect of interference.

Bibliography

1.P.A. Baranov, A.V. Vorontsov, S.V. Shevchenko. Social science: a complete reference book. Moscow 2013

2.Great Soviet Encyclopedia, 3rd edition (1969-1978), volume 23.

.A.V. Frolov, G.V. Frolov. Synthesis and recognition of speech. Modern solutions.

.Dushkov B.A., Korolev A.V., Smirnov B.A. Encyclopedic Dictionary: Psychology of work, management, engineering psychology and ergonomics. Moscow, 2005

.Kucherov A.G. Anatomy, physiology and research methods of the organ of hearing and balance. Moscow, 2002

.Stankov A.G. Human anatomy. Moscow, 1959

7.http://ioi-911. ucoz.ru/publ/1-1-0-47

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PHYSIOLOGY OF THE HEARING ANALYZER

(Auditory sensory system)

Lecture questions:

1. Structural and functional characteristics of the auditory analyzer:

a. outer ear

b. Middle ear

c. inner ear

2. Departments of the auditory analyzer: peripheral, conductive, cortical.

3. Perception of height, sound intensity and localization of the sound source:

a. Basic electrical phenomena in the cochlea

b. Perception of sounds of different heights

c. Perception of sounds of different intensity

d. Sound Source Identification (Binaural Hearing)

e. auditory adaptation

1. The auditory sensory system, the second most important distant human analyzer, plays an important role in humans in connection with the emergence of articulate speech.

Hearing analyzer function: transformation sound waves into the energy of nervous excitation and auditory feeling.

Like any analyzer, the auditory analyzer consists of a peripheral, conductive and cortical section.

PERIPHERAL DEPARTMENT

Converts sound wave energy into energy nervous excitation - receptor potential (RP). This department includes:

Inner ear (sound-perceiving apparatus);

middle ear (sound-conducting apparatus);

Outer ear (sound pickup).

The components of this department are combined into the concept hearing organ.

Functions of the departments of the organ of hearing

outer ear:

a) sound-catching (auricle) and directing the sound wave into the external auditory canal;

b) conducting a sound wave through the ear canal to the eardrum;

c) mechanical protection and protection from the temperature effects of the environment of all other parts of the hearing organ.

Middle ear(sound-conducting department) is a tympanic cavity with 3 auditory ossicles: hammer, anvil and stirrup.

The tympanic membrane separates the external auditory meatus from the tympanic cavity. The handle of the malleus is woven into the eardrum, its other end is articulated with the anvil, which, in turn, is articulated with the stirrup. The stirrup is adjacent to the membrane of the oval window. In the tympanic cavity, pressure equal to atmospheric pressure is maintained, which is very important for adequate perception of sounds. This function is performed by the Eustachian tube, which connects the middle ear cavity with the pharynx. When swallowing, the tube opens, as a result of which the tympanic cavity is ventilated and the pressure in it equalizes with atmospheric pressure. If the external pressure changes rapidly (rapid rise to a height), and swallowing does not occur, then the pressure difference between the atmospheric air and the air in the tympanic cavity leads to tension of the tympanic membrane and the appearance of unpleasant sensations (“ears stuffed up”), reducing the perception of sounds.

The area of the tympanic membrane (70 mm 2) is much larger than the area of the oval window (3.2 mm 2), due to which gain pressure of sound waves on the membrane of the oval window by 25 times. Bones linkage reduces the amplitude of sound waves by 2 times, therefore, the same amplification of sound waves occurs on the oval window of the tympanic cavity. Consequently, the middle ear amplifies the sound by about 60-70 times, and if we take into account the amplifying effect of the outer ear, this value increases by 180-200 times. In this regard, with strong sound vibrations, in order to prevent the destructive effect of sound on the receptor apparatus of the inner ear, the middle ear reflexively turns on a “protective mechanism”. It consists of the following: in the middle ear there are 2 muscles, one of them stretches the eardrum, the other fixes the stirrup. With strong sound effects, these muscles, when they are reduced, limit the amplitude of the oscillations of the tympanic membrane and fix the stirrup. This "quenches" the sound wave and prevents excessive excitation and destruction of the phonoreceptors of the organ of Corti.

inner ear: represented by a cochlea - a spirally twisted bone canal (2.5 curls in humans). This canal is divided along its entire length into three narrow parts (ladders) by two membranes: the main membrane and the vestibular membrane (Reissner).

On the main membrane there is a spiral organ - the organ of Corti (Corti's organ) - this is actually the sound-perceiving apparatus with receptor cells - this is the peripheral section of the auditory analyzer.

The helicotrema (foramen) connects the superior and inferior canals at the top of the cochlea. The middle channel is isolated.

Above the organ of Corti is a tectorial membrane, one end of which is fixed, while the other remains free. The hairs of the outer and inner hair cells of the organ of Corti come into contact with the tectorial membrane, which is accompanied by their excitation, i.e. the energy of sound vibrations is transformed into the energy of the excitation process.

The structure of the organ of Corti

The transformation process begins with sound waves entering the outer ear; they move the eardrum. Vibrations of the tympanic membrane are transmitted through the system of auditory ossicles of the middle ear to the membrane of the oval window, which causes vibrations of the perilymph of the vestibular scala. These vibrations are transmitted through the helicotrema to the perilymph of the scala tympani and reach the round window, protruding it towards the middle ear (this does not allow the sound wave to fade when passing through the vestibular and tympanic canals of the cochlea). The oscillations of the perilymph are transmitted to the endolymph, which causes oscillations of the main membrane. The fibers of the main membrane come into oscillatory motion together with the receptor cells (outer and inner hair cells) of the organ of Corti. In this case, the hairs of phonoreceptors are in contact with the tectorial membrane. The cilia of the hair cells are deformed, which causes the formation of a receptor potential, and on its basis, an action potential (nerve impulse), which is carried along the auditory nerve and transmitted to the next section of the auditory analyzer.

CONDUCTION DEPARTMENT OF THE HEARING ANALYZER

The conductive department of the auditory analyzer is presented auditory nerve. It is formed by the axons of the neurons of the spiral ganglion (the 1st neuron of the pathway). The dendrites of these neurons innervate the hair cells of the organ of Corti (afferent link), the axons form the fibers of the auditory nerve. The fibers of the auditory nerve end on the neurons of the nuclei of the cochlear body (VIII pair of MD) (the second neuron). Then, after a partial decussation, the fibers of the auditory pathway go to the medial geniculate bodies of the thalamus, where the switch again occurs (the third neuron). From here, excitation enters the cortex (temporal lobe, superior temporal gyrus, transverse Geschl gyrus) - this is the projection auditory cortex.

CORTICAL DEPARTMENT OF THE AUDIO ANALYZER

Represented in the temporal lobe of the cerebral cortex - superior temporal gyrus, transverse temporal gyrus of Heschl. Cortical gnostic auditory zones are associated with this projection zone of the cortex - Wernicke's sensory speech area and praxic zone - Broca's motor center of speech(inferior frontal gyrus). The friendly activity of the three cortical zones ensures the development and function of speech.

The auditory sensory system has feedbacks that provide regulation of the activity of all levels of the auditory analyzer with the participation of descending pathways that start from the neurons of the "auditory" cortex and sequentially switch in the medial geniculate bodies of the thalamus, the inferior tubercles of the quadrigemina of the midbrain with the formation of tectospinal descending pathways and on the nuclei cochlear body of the medulla oblongata with the formation of vestibulospinal tracts. This provides, in response to the action of a sound stimulus, the formation of a motor reaction: turning the head and eyes (and in animals - auricles) towards the stimulus, as well as increasing the tone of the flexor muscles (flexion of the limbs in the joints, i.e. readiness to jump or run ).

auditory cortex

PHYSICAL CHARACTERISTICS OF SOUND WAVES THAT ARE PERCEIVED BY THE ORGANIUM OF HEARING

1. The first characteristic of sound waves is their frequency and amplitude.

The frequency of sound waves determines the pitch!

A person distinguishes sound waves with a frequency 16 to 20,000 Hz (this corresponds to 10-11 octaves). Sounds whose frequency is below 20 Hz (infrasounds) and above 20,000 Hz (ultrasounds) by a person are not felt!

Sound that consists of sinusoidal or harmonic vibrations is called tone(high frequency - high tone, low frequency - low tone). A sound composed of unrelated frequencies is called noise.

2. The second characteristic of sound that the auditory sensory system distinguishes is its strength or intensity.

The strength of the sound (its intensity) together with the frequency (tone of the sound) is perceived as volume. The unit of loudness is bel = lg I / I 0, however, in practice it is more often used decibel (dB)(0.1 bela). A decibel is 0.1 decimal logarithm of the ratio of sound intensity to its threshold intensity: dB \u003d 0.1 lg I / I 0. The maximum volume level when the sound causes pain is 130-140 dB.

The sensitivity of the auditory analyzer is determined by the minimum sound intensity that causes auditory sensations.

In the region of sound vibrations from 1000 to 3000 Hz, which corresponds to human speech, the ear has the greatest sensitivity. This set of frequencies is called speech zone(1000-3000 Hz). The absolute sound sensitivity in this range is 1*10 -12 W/m 2 . At sounds above 20,000 Hz and below 20 Hz, the absolute auditory sensitivity decreases sharply - 1 * 10 -3 W / m 2. In the speech range, sounds are perceived that have a pressure less than 1/1000 bar (a bar is equal to 1/1,000,000 of normal atmospheric pressure). Based on this, in transmitting devices, in order to provide an adequate understanding of speech, information must be transmitted in the speech frequency range.

MECHANISM OF PERCEPTION OF HEIGHT (FREQUENCY), INTENSITY (POWER) AND LOCALIZATION OF SOUND SOURCE (BINAURAL HEARING)

Perception of the frequency of sound waves

The auditory analyzer is a combination of mechanical, receptor and nervous structures that perceive and analyze sound vibrations. The peripheral part of the auditory analyzer is represented by the auditory organ, consisting of the outer, middle and inner ear. The outer ear consists of the auricle and the external auditory meatus. The auricle of a newborn is flattened, its cartilage is soft, the skin is thin, the lobe is small. The auricle grows most rapidly during the first two years and after 10 years. It grows faster in length than in width. The eardrum separates the outer ear from the middle ear. The middle ear consists of the tympanic cavity, the auditory ossicles and the auditory tube.

The tympanic cavity in a newborn is the same size as in an adult. There are three auditory ossicles in the middle ear: the hammer, the anvil, and the inner ear, or labyrinth, has double walls: the membranous labyrinth is inserted into the bone one. The bony labyrinth consists of the vestibule, cochlea, and three semicircular canals. The cochlear duct divides the cochlea into two parts, or scalas. The inner ear of a newborn is well developed, its dimensions are close to those of an adult. The basal parts of the receptor cells come into contact with the nerve fibers that pass through the basement membrane and then exit into the canal of the spiral lamina. Then they go to the neurons of the spiral ganglion, which lies in the bony cochlea, where the conductive section of the auditory analyzer begins. The axons of the neurons of the spiral ganglion form the fibers of the auditory nerve, which enters the brain between the lower cerebellar peduncles and the pons and goes to the pons tegmentum, where the first intersection of the fibers takes place and a lateral loop is formed. Some of its fibers terminate on the cells of the inferior colliculus, where the primary auditory center is located. Other fibers of the lateral loop in the handle of the inferior colliculus approach the medial geniculate body. The processes of the cells of the latter form auditory radiance, ending in the cortex of the superior temporal gyrus (cortical section of the auditory analyzer).

The organ of Corti is the peripheral part of the auditory analyzer. Age features

The organ of Corti, located on the main membrane, contains receptors that convert mechanical vibrations into electrical potentials that excite the fibers of the auditory nerve. Under the action of sound, the main membrane begins to vibrate, the hairs of the receptor cells are deformed, which causes the generation of electrical potentials that reach the fibers of the auditory nerve through the synapses. The frequency of these potentials corresponds to the frequency of the sounds, and the amplitude depends on the intensity of the sound. As a result of the occurrence of electrical potentials, the fibers of the auditory nerve are excited, which are characterized by spontaneous activity even in silence (100 pulses / s). With sound, the frequency of impulses in the fibers increases during the entire time of the stimulus. For each nerve fiber, there is an optimal sound frequency that gives the highest discharge frequency and the lowest response threshold. If the spiral organ is damaged, high tones drop out at the base, low tones at the top. The destruction of the middle curl leads to the loss of tones of the middle frequency of the range. There are two mechanisms for pitch discrimination: spatial and temporal coding. Spatial coding is based on the unequal arrangement of excited receptor cells on the main membrane. At low and medium tones, temporal coding is also carried out. A person perceives sounds with a frequency of 16 to 20 000 Hz. This range corresponds to 10-11 octaves. The boundaries of hearing depend on age: the older the person, the more often he does not hear high tones. The difference in the frequency of sounds is characterized by the minimum difference in frequency of two sounds that a person catches. A person is able to notice a difference of 1-2 Hz. Absolute auditory sensitivity is the minimum strength of a sound heard by a person in half of the cases of its sound. In the region from 1000 to 4000 Hz, human hearing has maximum sensitivity. Speech fields also lie in this zone. The upper limit of audibility occurs when an increase in the volume of a sound of a constant frequency causes an unpleasant feeling of pressure and pain in the ear. The unit of sound volume is Bel. In everyday life, decibels are usually used as a unit of loudness, i.e. 0.1 bela. The maximum volume level when sound causes pain is 130-140 dB above the threshold of hearing. The auditory analyzer has two symmetrical halves (binaural hearing), i.e. a person is characterized by spatial hearing - the ability to determine the position of a sound source in space. The acuteness of such hearing is great. A person can determine the location of the sound source with an accuracy of 1 °.

Hearing in ontogeny

Despite the early development of the auditory analyzer, the organ of hearing in a newborn is not yet fully formed. He has relative deafness, which is associated with structural features of the ear. The newborn reacts to loud sounds with a start, a cessation of crying, a change in breathing. The hearing in children becomes quite distinct by the end of the 2nd - the beginning of the 3rd month. At the 2nd month of life, the child differentiates qualitatively different sounds, at 3-4 months he distinguishes pitch in the range from 1 to 4 octaves, at 4-5 months the sounds become conditioned stimuli, although conditioned food and defensive reflexes to sound stimuli are already developed from 3 -5 weeks of age. By the age of 1-2, children differentiate sounds, the difference between which is 1 tone, and by 4 years - even 3/4 and 1/2 tones. Hearing acuity is defined as the smallest amount of sound that can cause a sound sensation (hearing threshold). In an adult, the hearing threshold lies in the range of 10-12 dB, in children 6-9 years old - 17-24 dB, 10-12 years old - 14-19 dB. The greatest sharpness of sound is achieved by the middle and senior school age.

87 question. Myopia Preventionormyopia, astigmatism, hearing loss. Myopia is a visual impairment in which a person cannot see objects that are far away and sees close objects perfectly well. The disease is very common, it affects a third of the total population of the Earth. Myopia usually appears at the age of 7-15 years, may worsen or remain at the same level without changes throughout life.

Prevention of myopia: Proper lighting will reduce eye strain, so you should take care of the proper organization of the workplace, a table lamp. It is not recommended to work with a fluorescent lamp. Compliance with the regime of visual loads, alternating them with physical loads. Proper, balanced nutrition should contain a complex of essential vitamins and minerals: zinc, magnesium, vitamin A, etc. Strengthening the body through hardening, physical activity, massage, contrast shower. Monitor the correct posture of the child. These simple precautions minimize the chances of reduced distance vision, i.e. myopia. It is important to take all this into account for parents whose child has a hereditary tendency to the disease.

Children's astigmatism is such an optical defect when two optical foci exist simultaneously in the eye, moreover, none of them is where it should be. This is due to the fact that the cornea refracts rays along one axis more strongly than along the other.

Prevention.

Often, children simply do not notice that their vision is declining. So, even if there are no complaints, it is better to show the child to an ophthalmologist once a year. Then the disease will be detected on time, and treatment will be started. Eye exercises for astigmatism are quite useful. So, R.S. Agarwal advises to make large turns 100 times, move the gaze along the lines with a small print of the table for vision, combining them with blinking on each line.

Hearing loss - hearing loss of varying severity, in which speech perception is difficult, but possible when certain conditions are created (approaching the speaker or speaker to the ear, the use of sound amplifying equipment). With a combination of pathology of hearing and speech (deafness), children are not able to perceive and reproduce speech. Prevention of hearing loss and deafness in children is the most important way to solve the problem of hearing loss. Leading role in the prevention of hereditary forms of hearing loss. All pregnant women should be screened for kidney and liver disease, diabetes and other diseases. It is necessary to limit the prescription of ototoxic antibiotics to pregnant women and children, especially younger children. From the very first days of a child's life, the prevention of acquired forms of hearing loss should be combined with the prevention of diseases of the hearing aid, especially infectious-viral etiology. If the first signs of hearing impairment are detected, the child should be consulted by an otorhinolaryngologist.