The auditory sensory system and its functional significance. The structure of the auditory system

Hearing is a human sense organ that contributes to the mental development of a full-fledged personality and its adaptation in society. Hearing is associated with sound language communication. By using auditory analyzer a person perceives and distinguishes sound waves consisting of successive condensation and rarefaction of air.

The auditory analyzer consists of three parts: 1) the receptor apparatus contained in the inner ear; 2) pathways represented by the eighth pair of cranial (auditory) nerves; 3) hearing center in temporal lobe cerebral cortex.

Auditory receptors (phonoreceptors) are contained in the cochlea of ​​the inner ear, which is located in the pyramid of the temporal bone. Sound vibrations, before reaching the auditory receptors, pass through the entire system of sound-conducting and sound-amplifying parts.

Ear - This is an organ of hearing that consists of 3 parts: the outer, middle and inner ear.

Outer ear consists of the auricle and the external auditory canal. The outer ear is used to catch sounds. The auricle is formed by elastic cartilage and is covered with skin on the outside. At the bottom it is complemented by a fold - the lobe, which is filled with adipose tissue.

External auditory canal(2.5 cm), where sound vibrations are amplified by 2-2.5 times, is sent out by thin skin with fine hair and modified sweat glands that produce earwax, consisting of fat cells and containing pigment. Hairs and earwax play a protective role.

Middle ear consists of the eardrum, tympanic cavity and auditory tube. At the border between the outer and middle ear is the eardrum, which is covered externally by epithelium and internally by the auditory membrane. Sound vibrations that approach the eardrum cause it to vibrate at the same frequency. WITH inside the eardrum contains the tympanic cavity, inside which are located auditory ossicles, interconnected - hammer, anvil and stirrup. Vibrations from the eardrum are transmitted through the ossicular system to the inner ear. The auditory ossicles are placed so that they form levers that reduce the range of sound vibrations and increase their strength.

Tympanic cavity connected to the nasopharynx via eustachian tube, which maintains equal pressure from the outside and inside on the eardrum.

At the junction of the middle and inner ear is a membrane that contains oval window. The stapes is adjacent to the oval window of the inner ear.

Inner ear is located in the cavity of the pyramid of the temporal bone and is a bone labyrinth, inside of which there is membranous labyrinth from connective tissue. Between the bony and membranous labyrinths there is a fluid - perilymph, and inside the membranous labyrinth - endolymph. In the wall separating the middle ear from the inner ear, in addition to the oval window, there is also a round window, which makes vibrations of the fluid possible.

Bone labyrinth consists of three parts: in the center - the vestibule, in front of it snail, and behind - semicircular canals. Inside the middle canal of the cochlea, the cochlear duct contains a sound-receiving apparatus - a spiral or Corti's organ. It has a main lamina, which consists of approximately 24 thousand fibrous fibers. On the main plate along it in 5 rows there are supporting and hair sensory cells, which are actually auditory receptors. Hairs receptor cells washed by endolymph and in contact with the integumentary plate. The hair cells are covered by the nerve hairs of the cochlear branch of the auditory nerve. The medulla oblongata contains a second neuron auditory pathway, then this path goes, mostly crossing, to the posterior tubercles of the quadrigeminal, and from them to the temporal region of the cortex, where the central part of the auditory analyzer is located.

For the auditory analyzer, sound is an adequate stimulus. All vibrations of air, water and other elastic media are divided into periodic (tones) and non-periodic (noise). There are high and low tones. The main characteristic of each sound tone is the length of the sound wave, which corresponds to a certain number of vibrations per second. Sound wavelength determined by the distance that sound travels per second, divided by the number of complete vibrations carried out by the body that sounds, per second.

Human ear perceives sound vibrations within the range of 16-20,000 Hz, the strength of which is expressed in decibels (dB). Humans cannot hear sound vibrations with a frequency of more than 20 kHz. These are ultrasounds.

Sound waves- these are longitudinal vibrations of the medium. The strength of sound depends on the range (amplitude) of vibrations of air particles. The sound is characterized timbre or coloring.

The ear is most excitable to sounds with a frequency of oscillations from 1000 to 4000 Hz. Below and above this indicator, the excitability of the ear decreases.

In 1863 Helmholtz proposed resonance theory of hearing. Airborne sound waves entering the external auditory canal cause vibrations in the eardrum, which are then transmitted through the middle ear. The system of auditory ossicles, acting as a lever, amplifies sound vibrations and transmits them to the fluid contained between the bone and membranous labyrinths of the curls. Sound waves can also be transmitted through the air contained in the middle ear.

According to the resonance theory, vibrations of the endolymph cause vibrations of the main plate, the fibers of which have different lengths, tuned to different tones and form a set of resonators that sound in unison with various sound vibrations. The shortest waves are perceived at the base of the cochlea, and the long ones at the apex.

During the vibration of the corresponding resonating sections of the main plate, the sensitive hair cells located on it also vibrate. The smallest hairs of these cells touch when the integumentary plate oscillates and are deformed, which leads to excitation of the hair cells and conduction of impulses along the fibers of the cochlear nerve to the central nervous system. Since there is no complete isolation of the fibers of the main membrane, neighboring fibers begin to vibrate simultaneously, which corresponds to overtones. ABOUT Burton- a sound whose number of vibrations is 2, 4, 8, etc. times the number of vibrations of the fundamental tone.

With prolonged exposure to strong sounds, the excitability of the sound analyzer decreases, and with prolonged exposure to silence, excitability increases. This adaptation. The greatest adaptation is observed in the zone of higher sounds.

Excessive noise not only leads to hearing loss, but also causes mental disorders in people. Special experiments on animals have proven the possibility of the appearance "acoustic shock" and "acoustic snags", sometimes fatal.

6. Ear diseases and hearing hygiene. Prevention of the negative impact of “school” noise on the student’s body

Ear infection - otitis. The most common occurrence of otitis media is dangerous disease, because next to the middle ear cavity is the brain and its membranes. Otitis media most often occurs as a complication of influenza and acute respiratory diseases; an infection from the nasopharynx can pass through the Eustachian tube into the middle ear cavity. Otitis occurs as serious disease and manifests itself severe pain in the ear, high temperature body, severe headache, significant hearing loss. If these symptoms occur, you should immediately consult a doctor. Prevention of otitis: treatment of acute and chronic diseases of the nasopharynx (adenoids, runny nose, sinusitis). If you have a runny nose, you should not blow your nose too much so that the infection gets into the middle ear through the Eustachian tube. You cannot blow your nose with both halves of your nose at the same time, but you must do this alternately, pressing the wing of the nose to the nasal septum.

Deafness- complete loss of hearing in one or both ears. It can be acquired or congenital.

Acquired deafness most often it is a consequence of bilateral otitis media, which was accompanied by rupture of both eardrums or severe inflammation of the inner ear. Deafness can be caused by severe dystrophic lesions auditory nerves, which are often associated with professional factors: noise, vibration, exposure to chemical vapors or head injuries (for example, as a result of an explosion). Common cause deafness is otosclerosis- a disease in which the auditory ossicles (especially the stapes) become immobile. This disease was the cause of deafness in the outstanding composer Ludwig Van Beethoven. Deafness can be caused by uncontrolled use of antibiotics, which have a negative effect on the auditory nerve.

Congenital deafness associated with congenital disorder hearing the causes of which may be viral diseases of the mother during pregnancy (rubella, measles, influenza), uncontrolled use of certain medications, especially antibiotics, consumption of alcohol, drugs, smoking. A child born deaf, never hearing speech, becomes deaf and mute.

Hearing hygiene- a system of measures aimed at protecting hearing, creating optimal conditions for the activity of the auditory analyzer, promoting its normal development and functioning.

Distinguish specific and nonspecific the effect of noise on the human body. Specific action manifests itself in hearing impairment varying degrees, nonspecific- in various deviations in the activity of the central nervous system, disorders of autonomic reactivity, endocrine disorders, functional state of the cardiovascular system and digestive tract. In young and middle-aged people, at a noise level of 90 dB (decibels), which lasts for an hour, the excitability of cells in the cerebral cortex decreases, coordination of movements, visual acuity, stability of clear vision worsen, and the latent period of visual and auditory-motor reactions lengthens. For the same duration of operation in conditions of exposure to noise, the level of which is 96 dB, there is even more sudden violations cortical dynamics, phase states, extreme inhibition, autonomic reactivity disorders. Indicators of muscle performance (endurance, fatigue) and labor indicators deteriorate. Working in conditions of exposure to noise, the level of which is 120 dB, can cause disturbances in the form of asthenic and neurasthenic manifestations. Irritability, headaches, insomnia, and endocrine system disorders appear. Changes are taking place in cardiovascular system: vascular tone and heart rate are disrupted, blood pressure increases or decreases.

On adults and especially children it is extremely Negative influence(non-specific and specific) produces noise in rooms where radios, televisions, tape recorders, etc. are turned on at full volume.

Noise has a strong impact on children and adolescents. Changes in the functional state of the auditory and other analyzers are observed in children under the influence of “school” noise, the intensity level of which in the main premises of the school ranges from 40 to 110 dB. In the classroom, the noise intensity level is on average 50-80 dB, during breaks it can reach 95 dB.

Noise that does not exceed 40 dB does not cause negative changes in the functional state nervous system. Changes are noticeable when exposed to noise levels of 50-60 dB. According to research data, solving mathematical problems at a noise volume of 50 dB requires 15-55%, 60 dB - 81-100% more time than when exposed to noise. The weakening of the attention of schoolchildren under conditions of exposure to noise of the specified volume reached 16%. Reducing the levels of “school” noise and its adverse effects on the health of students is achieved through a number of complex measures: construction, technical and organizational.

Thus, the width of the “green zone” on the street side should be at least 6 m. It is advisable to plant trees along this strip at a distance of at least 10 m from the building, the crowns of which will delay the spread of noise.

Important in reducing "school" noise has hygienic correct location classrooms in the school building. Workshops, Sport halls located on the ground floor in a separate wing or annex.

The dimensions of classrooms must meet hygienic standards aimed at preserving the vision and hearing of students and teachers: length (size from the board to the opposite wall) and depth of classrooms. The length of the classroom, not exceeding 8 m, provides students with normal visual and hearing acuity, who sit on the last desks, a clear perception of the teacher’s speech and a clear vision of what is written on the board. The first and second desks (tables) in any row are reserved for students with impaired hearing, since speech is perceived from 2 to 4 m, and whispers from 0.5 to 1 m. Restore functional state auditory analyzer and prevent changes in other physiological systems Short breaks (10-15 minutes) help the teenager’s body.

Sensor system (analyzer)- called the part of the nervous system consisting of perceptive elements - sensory receptors, nerve pathways that transmit information from the receptors to the brain and parts of the brain that process and analyze this information

The sensor system includes 3 parts

1. Receptors - sense organs

2. Wiring department, connecting receptors to the brain

3. Section of the cerebral cortex, which perceives and processes information.

Receptors- a peripheral link designed to perceive stimuli from the external or internal environment.

Sensory systems have a general structure plan and sensory systems are characterized by

Multi-layering- presence of several layers nerve cells, the first of which is associated with receptors, and the latter with neurons of the motor areas of the cerebral cortex. Neurons are specialized for processing different types sensory information.

Multichannel- the presence of multiple parallel channels for processing and transmitting information, which ensures detailed signal analysis and greater reliability.

Different number of elements in adjacent layers, which forms the so-called “sensory funnels” (narrowing or expanding) They can ensure the elimination of redundancy of information or, conversely, a fractional and complex analysis of signal features

Differentiation of the sensory system vertically and horizontally. Vertical differentiation means the formation of sections of the sensory system, consisting of several neural layers (olfactory bulbs, cochlear nuclei, geniculate bodies).

Horizontal differentiation represents the presence of receptors and neurons with different properties within the same layer. For example, rods and cones in the retina process information differently.

The main task of the sensory system is the perception and analysis of the properties of stimuli, on the basis of which sensations, perceptions, and ideas arise. This constitutes the forms of a sensory, subjective reflection of the external world

Functions of touch systems

1. Signal detection. Each sensory system in the process of evolution has adapted to the perception of adequate stimuli inherent to a given system. The sensory system, for example the eye, can receive different - adequate and inadequate irritations (light or a blow to the eye). Sensory systems perceive force - the eye perceives 1 light photon (10 V -18 W). Eye shock(10V -4W). Electric current(10V -11W)
2. Signal discrimination.
3. Signal transmission or conversion. Any sensory system works as a transducer. It converts one form of energy from an active stimulus into energy nervous irritation. The sensory system should not distort the stimulus signal.

• May be spatial in nature
• Temporary transformations
• limitation of information redundancy (inclusion of inhibitory elements that inhibit neighboring receptors)
• Identification of essential signal features

1. Information coding - in the form of nerve impulses
2. Signal detection, etc. e. identifying signs of a stimulus that has behavioral significance
3. Provide image recognition
4. Adapt to stimuli
5. Interaction of sensory systems, which form the scheme of the surrounding world and at the same time allow us to relate ourselves to this scheme, for our adaptation. All living organisms cannot exist without receiving information from the environment. The more accurately an organism receives such information, the higher its chances will be in the struggle for existence.

Sensory systems are capable of responding to inappropriate stimuli. If you try the battery terminals, it causes a taste sensation - sour, this is the action electric current. This reaction of the sensory system to adequate and inadequate stimuli has raised the question for physiology - how much we can trust our senses.

Johann Müller formulated in 1840 the law of specific energy of the sense organs.

The quality of sensations does not depend on the nature of the stimulus, but is determined entirely by the specific energy inherent in the sensitive system, which is released when the stimulus acts.

With this approach, we can only know what is inherent in ourselves, and not what is in the world around us. Subsequent studies showed that excitations in any sensory system arise on the basis of one energy source - ATP.

Muller's student Helmholtz created symbol theory, according to which he considered sensations as symbols and objects of the surrounding world. The theory of symbols denied the possibility of knowing the world around us.

These 2 directions were called physiological idealism. What is a sensation? A sensation is a subjective image of the objective world. Sensations are images of the external world. They exist in us and are generated by the action of things on our senses. For each of us, this image will be subjective, i.e. it depends on the degree of our development, experience, and each person perceives surrounding objects and phenomena in his own way. They will be objective, i.e. this means that they exist, regardless of our consciousness. Since there is subjectivity of perception, then how to decide who perceives most correctly? Where will the truth be? The criterion of truth is Practical activities. Consistent learning is taking place. At each stage new information is obtained. The child tastes the toys and takes them apart into parts. It is from these deep experiences that we gain deeper knowledge about the world.

Classification of receptors.

1. Primary and secondary. Primary receptors represent a receptor ending that is formed by the very first sensory neuron (Pacinian corpuscle, Meissner's corpuscle, Merkel's disk, Ruffini's corpuscle). This neuron lies in spinal ganglion. Secondary receptors perceive information. Due to specialized nerve cells, which then transmit excitation to the nerve fiber. Sensitive cells of the organs of taste, hearing, balance.
2. Remote and contact. Some receptors perceive excitation through direct contact - contact, while others can perceive irritation at some distance - distant
3. Exteroceptors, interoreceptors. Exteroceptors- perceive irritation from the external environment - vision, taste, etc. and they provide adaptation to the environment. Interoreceptors- receptors of internal organs. They reflect the state of the internal organs and internal environment of the body.
4. Somatic - superficial and deep. Superficial - skin, mucous membranes. Deep - receptors of muscles, tendons, joints
5. Visceral
6. CNS receptors
7. Receptors of special senses - visual, auditory, vestibular, olfactory, gustatory

By the nature of information perception

1. Mechanoreceptors (skin, muscles, tendons, joints, internal organs)
2. Thermoreceptors (skin, hypothalamus)
3. Chemoreceptors (aortic arch, carotid sinus, medulla oblongata, tongue, nose, hypothalamus)
4. Photoreceptors (eye)
5. Pain (nociceptive) receptors (skin, internal organs, mucous membranes)

Mechanisms of receptor excitation

In the case of primary receptors, the action of the stimulus is perceived by the ending sensory neuron. An active stimulus can cause hyperpolarization or depolarization of the surface membrane receptors, mainly due to changes in sodium permeability. An increase in permeability to sodium ions leads to depolarization of the membrane and a receptor potential arises on the receptor membrane. It exists as long as the stimulus is in effect.

Receptor potential does not obey the “All or nothing” law; its amplitude depends on the strength of the stimulus. It has no refractory period. This allows the receptor potentials to be summed up during the action of subsequent stimuli. It spreads melenno, with extinction. When the receptor potential reaches a critical threshold, it causes an action potential to appear at the nearest node of Ranvier. At the node of Ranvier, an action potential arises, which obeys the “All or Nothing” law. This potential will be spreading.

In the secondary receptor, the action of the stimulus is perceived by the receptor cell. A receptor potential arises in this cell, the consequence of which will be the release of the transmitter from the cell into the synapse, which acts on the postsynaptic membrane of the sensitive fiber and the interaction of the transmitter with the receptors leads to the formation of another, local potential, which is called generator. Its properties are identical to receptor ones. Its amplitude is determined by the amount of released mediator. Mediators - acetylcholine, glutamate.

Action potentials occur periodically because They are characterized by a refractory period, when the membrane loses its excitability. Action potentials arise discretely and the receptor in the sensory system works like an analog-to-discrete converter. An adaptation is observed in the receptors - adaptation to the action of stimuli. There are those who adapt quickly and those who adapt slowly. During adaptation, the amplitude of the receptor potential and the number of nerve impulses that travel along the sensitive fiber decrease. Receptors encode information. It is possible by the frequency of potentials, by the grouping of impulses into separate volleys and the intervals between volleys. Coding is possible based on the number of activated receptors in the receptive field.

Threshold of irritation and threshold of entertainment.

Threshold of irritation- the minimum strength of the stimulus that causes a sensation.

Threshold of entertainment- the minimum force of change in the stimulus at which a new sensation arises.

Hair cells are excited when the hairs are displaced by 10 to -11 meters - 0.1 amstrom.

In 1934, Weber formulated a law establishing a relationship between the initial strength of stimulation and the intensity of sensation. He showed that the change in the strength of the stimulus is a constant value

∆I / Io = K Io=50 ∆I=52.11 Io=100 ∆I=104.2

Fechner determined that sensation is directly proportional to the logarithm of irritation

S=a*logR+b S-sensation R-irritation

S=KI in A Degree I - strength of irritation, K and A - constants

For tactile receptors S=9.4*I d 0.52

In sensory systems there are receptors for self-regulation of receptor sensitivity.

Influence of the sympathetic system - sympathetic system increases the sensitivity of receptors to the action of stimuli. This is useful in a situation of danger. Increases the excitability of receptors - reticular formation. Found in sensory nerves efferent fibers, which can change the sensitivity of receptors. Such nerve fibers are found in the auditory organ.

Sensory hearing system

For most people living in a modern shutdown, their hearing is progressively declining. This happens with age. This is facilitated by pollution from environmental sounds - vehicles, discotheques, etc. Changes in hearing aid become irreversible. The human ears contain 2 sensory organs. Hearing and balance. Sound waves propagate in the form of compression and discharge in elastic media, and the propagation of sounds in dense media is better than in gases. Sound has 3 important properties- pitch or frequency, power, or intensity and timbre. The pitch of sound depends on the vibration frequency and the human ear perceives frequencies from 16 to 20,000 Hz. With maximum sensitivity from 1000 to 4000 Hz.

The main frequency of the sound of a man's larynx is 100 Hz. Women - 150 Hz. When talking, additional high-frequency sounds appear in the form of hissing and whistling, which disappear when talking on the phone and this makes speech more understandable.

The power of sound is determined by the amplitude of vibrations. Sound power is expressed in dB. Power is a logarithmic relationship. Whispering speech - 30 dB, normal speech - 60-70 dB. The sound of transport is 80, the noise of an airplane engine is 160. A sound power of 120 dB causes discomfort, and 140 leads to painful sensations.

Timbre is determined by secondary vibrations on sound waves Oh. Ordered vibrations create musical sounds. And random vibrations simply cause noise. The same note sounds differently different instruments due to various additional fluctuations.

The human ear has 3 components - the outer, middle and inner ear. The outer ear is represented by the auricle, which acts as a sound-collecting funnel. The human ear picks up sounds less perfectly than the rabbit, and horses, which can control their ears. The auricle is based on cartilage, with the exception of the earlobe. Cartilage tissue gives elasticity and shape to the ear. If cartilage is damaged, it is restored by growing. The external auditory canal is S-shaped - inward, forward and downward, length 2.5 cm. The auditory canal is covered with skin with low sensitivity of the outer part and high sensitivity internal. The outer part of the ear canal contains hair that prevents particles from entering the ear canal. The glands of the ear canal produce a yellow lubricant, which also protects the ear canal. At the end of the passage is the eardrum, which consists of fibrous fibers covered on the outside with skin and on the inside with mucous membrane. The eardrum separates the middle ear from the outer ear. It vibrates with the frequency of the perceived sound.

The middle ear is represented by a tympanic cavity, the volume of which is approximately 5-6 drops of water and the tympanic cavity is filled with water, lined with a mucous membrane and contains 3 auditory ossicles: the malleus, the incus and the stirrup. The middle ear communicates with the nasopharynx via the Eustachian tube. At rest, the lumen of the Eustachian tube is closed, which equalizes the pressure. Inflammatory processes leading to inflammation of this tube cause a feeling of congestion. The middle ear is separated from the inner ear by an oval and round hole. Vibrations of the eardrum through a system of levers are transmitted by the stapes to the oval window, and the outer ear transmits sounds by air.

There is a difference in the area of ​​the tympanic membrane and the oval window (the area of ​​the tympanic membrane is 70 mm per sq. and that of the oval window is 3.2 mm per sq.). When vibrations are transferred from the membrane to the oval window, the amplitude decreases and the strength of vibrations increases by 20-22 times. At frequencies up to 3000 Hz, 60% of E is transmitted to the inner ear. In the middle ear there are 2 muscles that change vibrations: the tensor tympani muscle (attached to the central part of the eardrum and to the handle of the malleus) - as the force of contraction increases, the amplitude decreases; stapes muscle - its contractions limit the vibrations of the stapes. These muscles prevent injury to the eardrum. In addition to airborne sound transmission, there is also bone transfer, but this sound force is not able to cause vibrations in the bones of the skull.

Inner ear

The inner ear is a labyrinth of interconnected tubes and extensions. The organ of balance is located in the inner ear. The labyrinth has bone base, and inside there is a membranous labyrinth and there is endolymph. The auditory part includes the cochlea; it forms 2.5 revolutions around the central axis and is divided into 3 scalae: vestibular, tympanic and membranous. The vestibular canal begins with the membrane of the oval window and ends with the round window. At the apex of the cochlea, these 2 channels communicate using helicocream. And both of these channels are filled with perilymph. In the middle membranous canal there is a sound-receiving apparatus - the organ of Corti. The main membrane is built from elastic fibers that start at the base (0.04mm) and up to the apex (0.5mm). Toward the top, the fiber density decreases 500 times. The organ of Corti is located on the basilar membrane. It is built from 20-25 thousand special hair cells located on supporting cells. Hair cells lie in 3-4 rows (outer row) and in one row (inner). At the top of the hair cells there are stereocilia or kinocilia, the largest stereocilia. Sensitive fibers of the 8th pair of cranial nerves from the spiral ganglion approach the hair cells. In this case, 90% of the isolated sensory fibers end up on the inner hair cells. Up to 10 fibers converge on one inner hair cell. And in the composition nerve fibers There are also efferent ones (olivo-cochlear bundle). They form inhibitory synapses on sensory fibers from the spiral ganglion and innervate the outer hair cells. Irritation of the organ of Corti is associated with the transmission of ossicular vibrations to the oval window. Low-frequency vibrations propagate from the oval window to the apex of the cochlea (the entire main membrane is involved). low frequencies excitation of hair cells lying at the apex of the cochlea is observed. Bekashi studied the propagation of waves in the cochlea. He found that as the frequency increases, a smaller column of liquid is involved. High-frequency sounds cannot involve the entire column of fluid, so the higher the frequency, the less the perilymph vibrates. Vibrations of the main membrane can occur when sounds are transmitted through the membranous canal. When the main membrane oscillates, the hair cells shift upward, which causes depolarization, and if downward, the hairs deviate inward, which leads to hyperpolarization of the cells. When hair cells depolarize, Ca channels open and Ca promotes an action potential that carries information about sound. The external auditory cells have efferent innervation and the transmission of excitation occurs with the help of Ach on the external hair cells. These cells can change their length: they shorten with hyperpolarization and lengthen with polarization. Changing the length of the outer hair cells affects the oscillatory process, which improves the perception of sound by the inner hair cells. The change in hair cell potential is associated with the ionic composition of the endo- and perilymph. Perilymph resembles cerebrospinal fluid, while endolymph has high concentration K(150 mmol). Therefore, the endolymph acquires a positive charge to the perilymph (+80mV). Hair cells contain a lot of K; they have a membrane potential that is negatively charged inside and positive outside (MP = -70 mV), and the potential difference makes it possible for K to penetrate from the endolymph into the hair cells. Changing the position of one hair opens 200-300 K channels and depolarization occurs. Closure is accompanied by hyperpolarization. In Corti organ goes frequency coding due to excitation of different parts of the main membrane. At the same time, it was shown that low-frequency sounds can be encoded by the same number of nerve impulses as sound. Such encoding is possible when perceiving sound up to 500Hz. Encoding of sound information is achieved by increasing the number of fibers firing at a more intense sound and due to the number of activated nerve fibers. The sensory fibers of the spiral ganglion end in the dorsal and ventral nuclei of the cochlea of ​​the medulla oblongata. From these nuclei, the signal enters the olive nuclei of both its own and the opposite side. From her neurons come ascending paths as part of the lateral loop that approaches the lower tubercles of the quadrigeminal and the medial geniculate body of the optic tubercle. From the latter, the signal goes to the superior temporal gyrus (Heschl’s gyrus). This corresponds to fields 41 and 42 (primary zone) and field 22 (secondary zone). In the central nervous system there is a topotonic organization of neurons, that is, sounds with different frequencies and different intensities are perceived. The cortical center is important for perception, sound sequencing, and spatial localization. If field 22 is damaged, the definition of words is impaired (receptive opposition).

The nuclei of the superior olive are divided into medial and lateral parts. And the lateral nuclei determine the unequal intensity of sounds coming to both ears. The medial nucleus of the superior olive detects temporal differences in input sound signals. It was discovered that signals from both ears enter different dendritic systems of the same perceptive neuron. Violation auditory perception can manifest itself as ringing in the ears due to irritation of the inner ear or auditory nerve and two types of deafness: conductive and nerve. The first is associated with lesions of the outer and middle ear (cerumen plug). The second is associated with defects of the inner ear and lesions of the auditory nerve. Older people lose the ability to perceive high-frequency voices. Thanks to two ears, it is possible to determine the spatial localization of sound. This is possible if the sound deviates from the middle position by 3 degrees. When perceiving sounds, adaptation may develop due to the reticular formation and efferent fibers (by influencing the outer hair cells.

Visual system.

Vision is a multi-link process that begins with the projection of an image onto the retina of the eye, then there is excitation of photoreceptors, transmission and transformation in the neural layers of the visual system, and ends with the decision by the higher cortical parts of the visual image.

Structure and functions of the optical apparatus of the eye. The eye has a spherical shape, which is important for turning the eye. Light passes through several transparent media - the cornea, lens and vitreous body, which have certain refractive powers, expressed in diopters. Diopter is equal to the refractive power of a lens with a focal length of 100 cm. The refractive power of the eye when viewing distant objects is 59D, close objects are 70.5D. A smaller, inverted image is formed on the retina.

Accommodation- adaptation of the eye to clearly seeing objects at different distances. The lens plays a major role in accommodation. When viewing close objects, the ciliary muscles contract, the ligament of Zinn relaxes, and the lens becomes more convex due to its elasticity. When looking at the distant ones, the muscles are relaxed, the ligaments are tense and stretch the lens, making it more flattened. The ciliary muscles are innervated by parasympathetic fibers oculomotor nerve. Normally, the farthest point of clear vision is at infinity, the closest is 10 cm from the eye. The lens loses its elasticity with age, so the closest point of clear vision moves away and senile farsightedness develops.

Refractive errors of the eye.

Myopia (myopia). If the longitudinal axis of the eye is too long or the refractive power of the lens increases, the image is focused in front of the retina. The person has trouble seeing into the distance. Glasses with concave lenses are prescribed.

Farsightedness (hypermetropia). It develops when the refractive media of the eye decreases or when the longitudinal axis of the eye shortens. As a result, the image is focused behind the retina and the person has difficulty seeing nearby objects. Glasses with convex lenses are prescribed.

Astigmatism - unequal refraction of rays in different directions, due to the not strictly spherical surface of the cornea. They are compensated by glasses with a surface approaching cylindrical.

Pupil and pupillary reflex. The pupil is the hole in the center of the iris through which light rays pass into the eye. The pupil improves the clarity of the image on the retina, increasing the depth of field of the eye and by eliminating spherical aberration. If you cover your eye from light and then open it, the pupil quickly constricts - the pupillary reflex. In bright light the size is 1.8 mm, in medium light - 2.4, in the dark - 7.5. Enlargement results in poor image quality but increases sensitivity. The reflex has adaptive significance. The pupil is dilated by the sympathetic, and constricted by the parasympathetic. In healthy people, the sizes of both pupils are the same.

Structure and functions of the retina. The retina is the inner light-sensitive layer of the eye. Layers:

Pigmented - a series of process epithelial cells black color. Functions: screening (prevents the scattering and reflection of light, increasing clarity), regeneration of visual pigment, phagocytosis of fragments of rods and cones, nutrition of photoreceptors. The contact between the receptors and the pigment layer is weak, so this is where retinal detachment occurs.

Photoreceptors. Flasks are responsible for color vision, there are 6-7 million of them. Sticks for twilight, there are 110-123 million of them. They are located unevenly. IN fovea- only flasks, here - the greatest visual acuity. Sticks are more sensitive than flasks.

The structure of the photoreceptor. Consists of the outer receptive part - the outer segment, with visual pigment; connecting leg; nuclear part with presynaptic ending. The outer part consists of disks - a double-membrane structure. The outer segments are constantly updated. The presynaptic terminal contains glutamate.

Visual pigments. The sticks contain rhodopsin with absorption in the region of 500 nm. In the flasks - iodopsin with absorptions of 420 nm (blue), 531 nm (green), 558 (red). The molecule consists of the opsin protein and the chromophore part - retinal. Only the cis isomer perceives light.

Physiology of photoreception. When a quantum of light is absorbed, cis-retinal transforms into trans-retinal. This causes spatial changes in the protein part of the pigment. The pigment becomes discolored and becomes metarhodopsin II, which is able to interact with the near-membrane protein transducin. Transducin is activated and binds to GTP, activating phosphodiesterase. PDE breaks down cGMP. As a result, the concentration of cGMP falls, which leads to the closure of ion channels, while the sodium concentration decreases, leading to hyperpolarization and the emergence of a receptor potential that spreads throughout the cell to the presynaptic terminal and causes a decrease in the release of glutamate.

Restoration of the original dark state of the receptor. When metarhodopsin loses its ability to interact with transducin, guanylate cyclase, which synthesizes cGMP, is activated. Guanylate cyclase is activated by a drop in the concentration of calcium released from the cell by the exchange protein. As a result, the concentration of cGMP increases and it again binds to the ion channel, opening it. When opened, sodium and calcium enter the cell, depolarizing the receptor membrane, transferring it to a dark state, which again accelerates the release of the transmitter.

Retinal neurons.

Photoreceptors synapse with bipolar neurons. When light acts on the transmitter, the release of the transmitter decreases, which leads to hyperpolarization of the bipolar neuron. From the bipolar, the signal is transmitted to the ganglion. Impulses from many photoreceptors converge on a single ganglion neuron. The interaction of neighboring retinal neurons is ensured by horizontal and amacrine cells, the signals of which change synaptic transmission between receptors and bipolar (horizontal) and between bipolar and ganglion (amacrine). Amacrine cells exert lateral inhibition between adjacent ganglion cells. The system also contains efferent fibers that act on the synapses between bipolar and ganglion cells, regulating the excitation between them.

Nerve pathways.

The 1st neuron is bipolar.

2nd - ganglionic. Their processes are part of optic nerve, make a partial decussation (necessary to provide each hemisphere with information from each eye) and go to the brain as part of the optic tract, ending up in the lateral geniculate body of the thalamus (3rd neuron). From the thalamus - to the projection zone of the cortex, field 17. Here is the 4th neuron.

Visual functions.

Absolute sensitivity. For a visual sensation to occur, the light stimulus must have a minimum (threshold) energy. The stick can be excited by one quantum of light. Sticks and flasks differ little in excitability, but the number of receptors sending signals to one ganglion cell is different in the center and at the periphery.

Visual alaptation.

Adaptation of the visual sensory system to bright lighting conditions - light adaptation. The opposite phenomenon is dark adaptation. Increased sensitivity in the dark is gradual, due to the dark restoration of visual pigments. First, the iodopsin of the flasks is restored. This has little effect on sensitivity. Then rod rhodopsin is restored, which greatly increases sensitivity. For adaptation, the processes of changing connections between retinal elements are also important: weakening of horizontal inhibition, leading to an increase in the number of cells, sending signals to the ganglion neuron. The influence of the central nervous system also plays a role. When one eye is illuminated, it reduces the sensitivity of the other.

Differential visual sensitivity. According to Weber's law, a person will distinguish a difference in lighting if it is 1-1.5% stronger.

Luminance Contrast occurs due to mutual lateral inhibition of visual neurons. A gray stripe on a light background appears darker than gray on a dark background, since cells excited by a light background inhibit cells excited by a gray stripe.

Blinding brightness of light. Too bright light causes unpleasant feeling blindness. The upper limit of glare depends on the adaptation of the eye. The longer the dark adaptation, the less brightness causes blinding.

Inertia of vision. Visual sensation does not appear and disappear immediately. From irritation to perception it takes 0.03-0.1 s. Irritations that quickly follow one after another merge into one sensation. Minimum frequency The sequence of light stimuli at which the fusion of individual sensations occurs is called the critical frequency of flicker fusion. This is what the movie is based on. Sensations that continue after the cessation of irritation - successive images (the image of a lamp in the dark after it is turned off).

Color vision.

The entire visible spectrum from violet (400nm) to red (700nm).

Theories. Helmholtz's three-component theory. Color sensation provided by three types of bulbs, sensitive to one part of the spectrum (red, green or blue).

Hering's theory. The flasks contain substances sensitive to white-black, red-green and yellow-blue radiation.

Consistent color images. If you look at a painted object and then at White background, then the background will acquire an additional color. The reason is color adaptation.

Color blindness. Color blindness is a disorder in which it is impossible to distinguish between colors. Protanopia does not distinguish the color red. With deuteranopia - green. For tritanopia - blue. Diagnosed using polychromatic tables.

A complete loss of color perception is achromasia, in which everything is seen in shades of gray.

Perception of space.

Visual acuity- the maximum ability of the eye to distinguish individual details of objects. A normal eye distinguishes two points visible at an angle of 1 minute. Maximum acuity in the area macular spot. Determined by special tables.

Hearing is important in human life, which is primarily associated with the perception of speech. A person does not hear all sound signals, but only those that have biological and social significance for him. Since sound is propagating waves, the main characteristics of which are frequency and amplitude, hearing is characterized by the same parameters. Frequency is subjectively perceived as the tonality of a sound, and amplitude as its intensity and volume. The human ear is capable of perceiving sounds with a frequency from 20 Hz to 20,000 Hz and an intensity of up to 140 dB (pain threshold). The most sensitive hearing lies in the range of 1–2 thousand Hz, i.e. in the field of speech signals.

The peripheral section of the auditory analyzer - the organ of hearing, consists of the outer, middle and inner ear (Fig. 4).

Rice. 4. Human ear: 1 – auricle; 2 – external auditory canal; 3 – eardrum; 4 – Eustachian tube; 5 – hammer; 6 – anvil; 7 – stirrup; 8 – oval window; 9 – snail.

Outer ear includes auricle and external auditory canal. These structures act as a horn and concentrate sound vibrations in a certain direction. The auricle is also involved in determining the localization of sound.

Middle ear includes the eardrum and auditory ossicles.

The eardrum, which separates the outer ear from the middle ear, is a 0.1 mm thick septum woven from fibers running in different directions. In its shape, it resembles a funnel directed inward. The eardrum begins to vibrate when sound vibrations pass through the external auditory canal. The vibrations of the eardrum depend on the parameters of the sound wave: the higher the frequency and volume of the sound, the higher the frequency and greater the amplitude of the vibrations of the eardrum.

These vibrations are transmitted to the auditory ossicles - the malleus, incus and stapes. The surface of the stapes is adjacent to the membrane of the oval window. The auditory ossicles form a system of levers between themselves, which amplifies the vibrations transmitted from the eardrum. The ratio of the surface of the stapes to the tympanic membrane is 1:22, which increases the pressure of sound waves on the oval window membrane by the same amount. This circumstance is of great importance, since even weak sound waves acting on the eardrum are able to overcome the resistance of the oval window membrane and set in motion a column of fluid in the cochlea. Thus, the vibrational energy transmitted to the inner ear increases approximately 20 times. However, with very loud sounds, the same system of bones, with the help of special muscles, weakens the transmission of vibrations.

In the wall separating the middle ear from the inner ear, in addition to the oval one, there is also a round window, also covered with a membrane. Fluid oscillations in the cochlea, which arose at the oval window and passed along the cochlea's passages, reach the round window without damping. If this window with a membrane did not exist, due to the incompressibility of the liquid, its vibrations would be impossible.

The middle ear cavity communicates with the external environment through eustachian tube, which ensures that a constant pressure close to atmospheric pressure is maintained in the cavity, which creates the most favorable conditions for vibrations of the eardrum.

Inner ear(labyrinth) includes the auditory and vestibular receptor apparatus. The auditory part of the inner ear - the cochlea - is a spirally twisted, gradually expanding bone canal (in humans, 2.5 turns, stroke length about 35 mm) (Fig. 5).

Along its entire length, the bone canal is divided by two membranes: a thinner vestibular (Reissner) membrane and a more dense and elastic main (basilar, basal) membrane. At the top of the cochlea, both of these membranes are connected and there is an opening in them - the helicotrema. The vestibular and basilar membranes divide the bony canal into three fluid-filled passages or stairs.

The upper canal of the cochlea, or scala vestibular, originates from the oval window and continues to the apex of the cochlea, where it communicates through the helicotrema with the lower canal of the cochlea, the scala tympani, which begins in the region of the round window. The upper and lower canals are filled with perilymph, which resembles cerebrospinal fluid in composition. The middle - membranous canal (scala cochlea) does not communicate with the cavity of other canals and is filled with endolymph. On the basilar (main) membrane in the scala cochlea the receptor apparatus of the cochlea is located - Corti organ consisting of hair cells. Above the hair cells is a tectorial membrane. When sound vibrations are transmitted through the system of auditory ossicles to the cochlea, the latter vibrates the fluid and, accordingly, the membrane on which the hair cells are located. The hairs touch the tectorial membrane and become deformed, which is the direct cause of the excitation of receptors and the generation of receptor potential. The receptor potential causes the release of a mediator, acetylcholine, at the synapse, which in turn leads to the generation of action potentials in the auditory nerve fibers. This excitation is then transmitted to the nerve cells of the spiral ganglion of the cochlea, and from there to the auditory center of the medulla oblongata - the cochlear nuclei. After switching on the neurons of the cochlear nuclei, the impulses arrive to the next cell cluster - the nuclei of the superior olivary pontine complex. All afferent pathways from the cochlear nuclei and nuclei of the superior olive complex end in the posterior colliculus, or inferior colliculus, the auditory center of the midbrain. From here nerve impulses enter the internal geniculate body of the thalamus, the processes of the cells of which are directed to the auditory cortex. The auditory cortex is located in the upper part of the temporal lobe and includes areas 41 and 42 (according to Brodmann).

In addition to the ascending (afferent) auditory pathway, there is also a descending centrifugal, or efferent, pathway designed to regulate sensory flow

.Principles of processing auditory information and basics of psychoacoustics

The main parameters of sound are its intensity (or sound pressure level), frequency, duration and spatial localization of the sound source. What mechanisms underlie the perception of each of these parameters?

Sound intensity at the receptor level it is encoded by the amplitude of the receptor potential: the louder the sound, the greater the amplitude. But here, as in the visual system, there is not a linear, but a logarithmic dependence. Unlike the visual system, the auditory system also uses another method - coding by the number of excited receptors (due to different threshold levels in different hair cells).

In the central parts of the auditory system, with increasing intensity, as a rule, the frequency of nerve impulses increases. However, for central neurons, the most significant is not the absolute level of intensity, but the nature of its change over time (amplitude-temporal modulation).

Frequency of sound vibrations. Receptors on basement membrane are located in a strictly defined order: on the part located closer to the oval window of the cochlea, the receptors react to high frequencies, and the membranes located on the part closer to the apex of the cochlea react to low frequencies. Thus, the frequency of sound is encoded by the location of the receptor on the basement membrane. This coding method is also preserved in the overlying structures, since they are a kind of “map” of the basement membrane and the relative position of the nerve elements here exactly corresponds to that on the basement membrane. This principle is called topical. At the same time, it should be noted that at high levels of the sensory system, neurons no longer respond to a pure tone (frequency), but to its change in time, i.e. to more complex signals, which, as a rule, have one or another biological significance.

Sound duration is encoded by the duration of the discharge of tonic neurons, which are capable of being excited during the entire duration of the stimulus.

Spatial sound localization is provided mainly by two different mechanisms. Their activation depends on the frequency of the sound or its wavelength. With low-frequency signals (up to approximately 1.5 kHz), the wavelength is less than the interear distance, which is on average 21 cm in humans. In this case, the source is localized due to the different time of arrival of the sound wave at each ear depending on the azimuth. At frequencies greater than 3 kHz, the wavelength is obviously less than the inter-ear distance. Such waves cannot go around the head; they are repeatedly reflected from surrounding objects and the head, losing the energy of sound vibrations. In this case, localization is carried out mainly due to interaural differences in intensity. In the frequency range from 1.5 Hz to 3 kHz, the temporary localization mechanism changes to the intensity estimation mechanism, and the transition region turns out to be unfavorable for determining the location of the sound source.

When determining the location of a sound source, it is important to assess its distance. Signal intensity plays a significant role in solving this problem: the greater the distance from the observer, the lower the perceived intensity. At large distances (more than 15 m), we take into account the spectral composition of the sound that has reached us: high-frequency sounds decay faster, i.e. “run” a shorter distance; low-frequency sounds, on the contrary, attenuate more slowly and spread further. This is why sounds made by a distant source seem lower to us. One of the factors that significantly facilitates the assessment of distance is the reverberation of the sound signal from reflective surfaces, i.e. perception of reflected sound.

The auditory system is capable of determining not only the location of a stationary, but also a moving sound source. The physiological basis for assessing the localization of a sound source is the activity of the so-called motion detector neurons located in the superior olivary complex, dorsal colliculus, internal geniculate body and auditory cortex. But the leading role here belongs to the upper olive trees and the rear hills.

Questions and tasks for self-control

1. Consider the structure of the hearing organ. Describe the functions of the external ear.

2. What is the role middle ear in the transmission of sound vibrations?

3. Consider the structure of the cochlea and the organ of Corti.

4. What are auditory receptors and what is the immediate cause of their excitation?

5. How is sound vibrations converted into nerve impulses?

6. Describe the central sections of the auditory analyzer.

7. Describe the mechanisms of sound intensity coding at different levels of the auditory system?

8. How is sound frequency encoded?

9. What mechanisms of spatial localization of sound do you know?

10. In what frequency range does the human ear perceive sounds? Why do the lowest intensity thresholds in humans lie in the region of 1–2 kHz?

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

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

Table 12.2.

Structure and functions of the ear

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

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

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

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

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

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

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

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

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

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

Binaural hearing. Humans and animals have spatial hearing, i.e. the ability to determine the position of a sound source in space. This property is based on the presence of two symmetrical halves of the auditory analyzer (binaural hearing).

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

The hearing analyzer is the second most important analyzer in providing cognitive activity person. The auditory system serves to perceive sound signals, which gives it a special role associated with the perception of articulate speech. A child who loses his hearing in early childhood also loses his speech ability.

Structure of the auditory analyzer:

The peripheral part is the receptor apparatus in the ear (inner);

The conductor part is the auditory nerve;

The central part is the auditory zone of the cerebral cortex (temporal lobe).

Structure of the ear.

The ear is an organ of hearing and balance, includes:

The outer ear is the auricle that captures sound vibrations and directs them to the external auditory canal. The auricle is formed by elastic cartilage, covered on the outside with skin. The external auditory canal looks like a curved canal 2.5 cm long. Its skin is covered with hairs. The gland ducts that produce earwax open into the ear canal. Both hairs and earwax perform a protective function;

Middle ear. Consists of: eardrum, tympanic cavity (filled with air), auditory ossicles - malleus, incus, stirrup (transmit sound vibrations from the eardrum to the oval window of the inner ear, prevent its overload), eustachian tube (connects the middle ear cavity with the pharynx). The eardrum is a thin elastic plate located on the border of the outer and middle ear. The malleus is connected at one end to the eardrum, and at the other end to the incus, which is connected to the stapes. The stapes is connected to the oval window, which separates tympanic cavity from the inner ear. The auditory (Eustachian) tube connects the tympanic cavity with the nasopharynx, lined from the inside with mucous membrane. It maintains equal pressure externally and internally on the eardrum.

The middle ear is separate from the inner ear bone wall, in which there are two holes (round window and oval window);

Inner ear. Located in the temporal bone and formed by the bony and membranous labyrinths. The membranous labyrinth of connective tissue is located inside the bony labyrinth. Between the bony and membranous labyrinth there is a fluid - perilymph, and inside the membranous labyrinth - endolymph.

The bony labyrinth consists of the cochlea (sound-receiving apparatus), the vestibule (part vestibular apparatus) and three semicircular canals (the organ of hearing and balance). The membranous labyrinth is located inside the bony labyrinth. Between them there is a liquid - perilymph, and inside the membranous labyrinth - endolymph. In the membranous labyrinth of the cochlea there is the organ of Corti - the receptor part of the auditory analyzer, which converts sound vibrations into nervous excitement. The bony vestibule, which forms the middle part of the labyrinth of the inner ear, has two open windows, oval and round, which connect the bone cavity with the eardrum. The oval window is closed by the base of the stapes, and the round window is covered by a movable elastic connective tissue plate.

Sound perception: sound waves through the auricle enter the external auditory canal and cause oscillatory movements of the eardrum - vibrations of the eardrum are transmitted to the auditory ossicles, the movements of which cause vibration of the stapes, which closes the oval window - movements of the stapes of the oval window vibrate the perilymph, its vibrations are transmitted - oscillation endolymph, entails vibration of the main membrane - during the movements of the main membrane and endolymph, the integumentary membrane inside the cochlea with a certain force and frequency touches the microvilli of receptor cells, which are excited - excitation by auditory nerve to the subcortical hearing centers ( midbrain) –– higher analysis and the synthesis of auditory stimuli occurs in cortical center auditory analyzer, which is located in the temporal lobe. Here the character of the sound, its strength, and height are distinguished.