Topic 5. ANALYZERS. HYGIENE OF VISION AND HEARING

5.1. The concept of analyzers

An analyzer (sensory system) is a part of the nervous system, consisting of many specialized perceiving receptors, as well as intermediate and central nerve cells and nerve fibers connecting them. For sensation to occur, the following functional elements must be present:

1) sensory organ receptors that perform a perceiving function (for example, for a visual analyzer, these are retinal receptors);

2) a centripetal path from this sense organ to the cerebral hemispheres, providing a conductive function (for example, optic nerves and pathways through the diencephalon);

3) the perceiving zone in the cerebral hemispheres, which implements the analyzing function (the visual zone in the occipital region of the cerebral hemispheres).

Receptor specificity. Receptors are specialized formations adapted to perceive certain influences of the external and internal environment. Receptors have specificity, i.e., high excitability only to certain stimuli, called adequate. In particular, for the eye an adequate stimulus is light, and for the ear - sound waves, etc. When adequate stimuli act, sensations arise that are characteristic of a particular sense organ. Thus, irritation of the eye causes visual sensations, ear - auditory sensations, etc. In addition to adequate ones, there are also inadequate (inadequate) stimuli that cause only a small part of the sensations characteristic of a given sense organ, or act in an unusual way. For example, mechanical or electrical irritation of the eye is perceived as a bright flash of light ("phosphene"), but does not give an image of an object and the perception of colors. The specificity of the sense organs is the result of the body's adaptation to environmental conditions.

Each receptor is characterized by the following properties:

a) a certain value of the threshold of excitability, i.e., the smallest strength of the stimulus that can cause a sensation;

b) chronaxia;

c) time threshold - the smallest interval between two stimuli, at which two sensations differ;

d) discrimination threshold - the smallest increase in the strength of the stimulus, causing a barely noticeable difference in sensation (for example, in order to distinguish the difference in the pressure of the load on the skin with closed eyes, you need to add about 3,2-5,3% of the initial load);

e) adaptation - a sharp drop (increase) in the strength of sensation immediately after the onset of the stimulus. Adaptation is based on a decrease in the frequency of excitation waves that occurs in the receptor when it is stimulated.

Organs of taste. The epithelium of the oral mucosa contains taste buds that have a round or oval shape. They consist of oblong and flat cells located at the base of the bulb. Elongated cells are divided into supporting cells (located on the periphery) and taste cells (located in the center). Each taste bud contains from two to six taste cells, and their total number in an adult reaches 9 thousand. Taste buds are located in the papillae of the mucous membrane of the tongue. The apex of the taste bud does not reach the surface of the epithelium, but communicates with the surface using the taste canal. Individual taste buds are located on the surface of the soft palate, the posterior wall of the pharynx, and the epiglottis. Centripetal impulses from each taste bud are carried along two or three nerve fibers. These fibers are part of the chorda tympani and the lingual nerve, which innervate the anterior two-thirds of the tongue, and from the posterior third they form part of the glossopharyngeal nerve. Next, through the visual hillocks, centripetal impulses enter the taste zone of the cerebral hemispheres.

Olfactory organs. Olfactory receptors are located in the upper part of the nasal cavity. Olfactory cells are neurons surrounded by supporting columnar cells. Humans have 60 million olfactory cells, the surface of each of them is covered with cilia, which increase the olfactory surface, which in humans is approximately 5 square meters. see. From the olfactory cells, centripetal impulses along nerve fibers passing through the holes in the ethmoid bone enter the olfactory nerve, and then through the subcortical centers, where the second and third neurons are located, enter the olfactory zone of the cerebral hemispheres. Since the olfactory surface is located away from the respiratory tract, air with odorous substances penetrates to it only by diffusion.

Skin sensitivity organs. Skin receptors are divided into tactile (their irritation causes sensations of touch), thermoreceptors (cause sensations of heat and cold) and pain receptors.

The sensations of touch, or touch and pressure, differ in character, for example, one cannot feel the pulse with the tongue. There are approximately 500 tactile receptors in human skin. The threshold of excitability of tactile receptors in different parts of the body is not the same: the highest excitability in the receptors of the skin of the nose, fingertips and mucous membrane of the lips, the smallest - in the skin of the abdomen and inguinal region. For tactile receptors, the simultaneous spatial threshold (the smallest distance between receptors at which simultaneous skin irritation causes two sensations) is the smallest, for pain receptors it is the largest. Tactile receptors also have the smallest time threshold, that is, the time interval between two successive stimuli at which two separate sensations are evoked.

The total number of thermoreceptors is about 300 thousand, of which 250 thousand are thermal, and 30 thousand are cold. Cold receptors are located closer to the surface of the skin, and thermal receptors are deeper.

There are from 900 thousand to 1 million pain receptors. Pain is stimulated by defensive reflexes of the skeletal muscles and internal organs, but prolonged strong irritation of pain receptors causes a violation of many body functions. Pain sensations are more difficult to localize than other types of skin sensitivity, since the excitation that occurs when pain receptors are irritated widely radiates through the nervous system. Simultaneous irritation of the receptors of vision, hearing, smell and taste reduces the sensation of pain.

Vibration sensations (oscillations of objects with a frequency of 2-10 times per second) are well perceived by the skin of the fingers and the bones of the skull. Centripetal impulses from skin receptors enter the spinal cord through the posterior roots and reach the neurons of the posterior horns. Then, along the nerve fibers that make up the posterior columns (gentle and wedge-shaped bundles) and the lateral (spinal-thalamic bundle), the impulses reach the anterior nuclei of the visual tubercles. From here, the fibers of the third neuron begin, which, together with the fibers of proprioceptive sensitivity, reach the zone of musculoskeletal sensitivity in the posterior central gyrus of the cerebral hemispheres.

5.2. organs of vision. The structure of the eye

The eyeball consists of three shells: outer, middle and inner. The outer, or fibrous, membrane is formed from dense connective tissue - the cornea (in front) and the opaque sclera, or tunica (back). The middle (vascular) membrane contains blood vessels and consists of three sections:

1) anterior section (iris, or iris). The iris contains smooth muscle fibers that make up two muscles: a circular, constricting pupil, located almost in the center of the iris, and a radial, dilating the pupil. Closer to the anterior surface of the iris is a pigment that determines the color of the eye and the opacity of this shell. The iris adjoins with its back surface to the lens;

2) middle section (ciliary body). The ciliary body is located at the junction of the sclera with the cornea and has up to 70 ciliary radial processes. Inside the ciliary body is the ciliary, or ciliary, muscle, which consists of smooth muscle fibers. The ciliary muscle is attached by ciliary ligaments to the tendon ring and the lens bag;

3) the posterior section (the choroid itself).

The inner shell (retina) has the most complex structure. The main receptors in the retina are rods and cones. There are about 130 million rods and about 7 million cones in the human retina. Each rod and cone has two segments - an outer and an internal one; the cone has a shorter outer segment. The outer segments of the rods contain visual purple, or rhodopsin (purple-colored substance), and the outer segments of the cones contain iodopsin (purple color). The internal segments of the rods and cones are connected to neurons that have two processes (bipolar cells), which are in contact with ganglion neurons, which are part of the optic nerve with their fibers. Each optic nerve contains about 1 million nerve fibers.

The distribution of rods and cones in the retina has the following order: in the middle of the retina there is a central fovea (yellow spot) with a diameter of 1 mm, it contains only cones, closer to the central fovea are cones and rods, and on the periphery of the retina - only rods. In the fovea, each cone is connected to one neuron through a bipolar cell, and to the side of it, several cones are also connected to one neuron. Rods, unlike cones, are connected to one bipolar cell in several pieces (about 200). Due to this structure, the greatest visual acuity is provided in the fovea. At a distance of approximately 4 mm medially from the central fossa is the papilla of the optic nerve (blind spot), in the center of the nipple are the central artery and the central vein of the retina.

Between the posterior surface of the cornea and the anterior surface of the iris and part of the lens is the anterior chamber of the eye. Between the posterior surface of the iris, the anterior surface of the ciliary ligament and the anterior surface of the lens is the posterior chamber of the eye. Both chambers are filled with transparent aqueous humor. The entire space between the lens and the retina is occupied by a transparent vitreous body.

Light refraction in the eye. The light-refracting media of the eye include: the cornea, the aqueous humor of the anterior chamber of the eye, the lens and the vitreous body. Much of the clarity of vision depends on the transparency of these media, but the refractive power of the eye depends almost entirely on refraction in the cornea and lens. Refraction is measured in diopters. Diopter is the reciprocal of focal length. The refractive power of the cornea is constant and equal to 43 diopters. The refractive power of the lens is not constant and varies widely: when viewing at a close distance - 33 diopters, at a distance - 19 diopters. The refractive power of the entire optical system of the eye: when looking into the distance - 58 diopters, at a close distance - 70 diopters.

Parallel light rays, after refraction in the cornea and lens, converge to one point in the fovea. The line passing through the centers of the cornea and lens to the center of the macula is called the visual axis.

Accommodation. The ability of the eye to clearly distinguish objects located at different distances is called accommodation. The phenomenon of accommodation is based on the reflex contraction or relaxation of the ciliary, or ciliary, muscle innervated by the parasympathetic fibers of the oculomotor nerve. Contraction and relaxation of the ciliary muscle changes the curvature of the lens:

a) when the muscle contracts, the ciliary ligament relaxes, which causes an increase in light refraction, because the lens becomes more convex. Such a contraction of the ciliary muscle, or visual tension, occurs when an object approaches the eye, that is, when viewing an object that is as close as possible;

b) when the muscle relaxes, the ciliary ligaments stretch, the lens bag squeezes it, the curvature of the lens decreases and its refraction decreases. This occurs when the object is removed from the eye, i.e., when looking into the distance.

The contraction of the ciliary muscle begins when an object approaches a distance of about 65 m, then its contractions increase and become distinct when an object approaches a distance of 10 m. Further, as the object approaches, the contractions of the muscles increase more and more and finally reach the limit at which clear vision becomes impossible. The minimum distance from an object to the eye at which it is clearly visible is called the nearest point of clear vision. In a normal eye, the far point of clear vision is at infinity.

Farsightedness and myopia. A healthy eye, when looking into the distance, refracts a beam of parallel rays so that they are focused in the central fovea. With myopia, parallel rays gather in focus in front of the fovea, diverging rays enter it and therefore the image of the object blurs. The causes of myopia may be tension in the ciliary muscle when accommodating close distances or the longitudinal axis of the eye being too long.

In farsightedness (due to a short longitudinal axis), parallel rays are focused behind the retina, and converging rays enter the fovea, which also causes blurred images.

Both vision defects can be corrected. Myopia is corrected by biconcave lenses, which reduce refraction and shift the focus to the retina; farsightedness - biconvex lenses that increase the refraction and therefore move the focus to the retina.

5.3. Light and color sensitivity. Light-receiving function

Under the action of light rays, a photochemical cleavage reaction of rhodopsin and iodopsin occurs, and the reaction rate depends on the wavelength of the beam. The splitting of rhodopsin in the light gives a light sensation (colorless), iodopsin - color. Rhodopsin is cleaved much faster than iodopsin (about 1000 times), so the excitability of rods to light is greater than that of cones. This allows you to see at dusk and in low light.

Rhodopsin consists of the protein opsin and oxidized vitamin A (retinene). Iodopsin also consists of a combination of retinene with the protein opsin, but of a different chemical composition. In the dark, with sufficient intake of vitamin A, the restoration of rhodopsin and iodopsin increases, therefore, with an excess of vitamin A (hypovitaminosis), a sharp deterioration in night vision occurs - hemeralopia. The difference in the rate of splitting of rhodopsin and iodopsin leads to a difference in the signals entering the optic nerve.

As a result of a photochemical reaction, the resulting excitation from the ganglion cells is transmitted along the optic nerve to the external geniculate bodies, where the primary signal processing takes place. Then the impulses are transmitted to the visual areas of the cerebral hemispheres, where they are decoded into visual images.

Color perception. The human eye perceives light rays of different wavelengths from 390 to 760 nm: red - 620-760, orange - 585-620, yellow - 575-585, green-yellow - 550-575, green - 510-550, blue - 480- 510, blue - 450-480, purple - 390-450. Light rays having a wavelength less than 390 nm and more than 760 nm are not perceived by the eye. The most widespread theory of color perception, the main provisions of which were first expressed by M.V. Lomonosov in 1756, and further developed by the English scientist Thomas Young (1802) and G.L.F. Helmholtz (1866) and confirmed by data from modern morphophysiological and electrophysiological studies, is as follows.

There are three types of cones, each of which contains only one color-reactive substance that is excitable to one of the primary colors (red, green or blue), as well as three groups of fibers, each of which conducts impulses from one type of cone. The color stimulus acts on all three types of cones, but to varying degrees. Different combinations of the degree of excitation of cones create different color sensations. With equal irritation of all three types of cones, a sensation of white color occurs. This theory is called the three-component color theory.

Features of vision coordination in newborns. A child is born seeing, but his clear, clear vision has not yet developed. In the first days after birth, children's eye movements are not coordinated. Thus, one can observe that the child’s right and left eyes move in opposite directions, or when one eye is immobile, the other moves freely. During the same period, uncoordinated movements of the eyelids and eyeball are observed (one eyelid may be open and the other lowered). The development of visual coordination occurs by the second month of life.

The lacrimal glands in a newborn are developed normally, but he cries without tears - there is no protective lacrimal reflex due to the underdevelopment of the corresponding nerve centers. Tears when crying in children appear after 1,2-2 months.

5.4. Light regime in educational institutions

As a rule, the educational process is closely associated with significant visual strain. A normal or slightly increased level of illumination of school premises (classrooms, classrooms, laboratories, educational workshops, assembly halls, etc.) helps to reduce the tension of the nervous system, maintain working capacity and maintain an active state of students.

Sunlight, in particular ultraviolet rays, promote the growth and development of the child's body, reduce the risk of the spread of infectious diseases, and provide the formation of vitamin D in the body.

With insufficient lighting in the classrooms, schoolchildren tilt their heads too low when reading, writing, etc. This causes increased blood flow to the eyeball, which puts additional pressure on it, which leads to a change in its shape and contributes to the development of myopia. To avoid this, it is desirable to ensure the penetration of direct sunlight into the school premises and strictly observe the rules of artificial lighting.

Daylight. The illumination of the student's and teacher's workplace by direct or reflected rays of the sun depends on several parameters: the location of the school building on the site (orientation), the interval between tall buildings, compliance with the natural illumination coefficient, and the light coefficient.

The natural illuminance coefficient (LKR) is the ratio of the illuminance (in lux) indoors to the illuminance at the same level outdoors, expressed as a percentage. This coefficient is considered the main indicator of classroom illumination. It is determined using a luxmeter. The minimum allowable KEO for classrooms in areas of central Russia is 1,5%. In northern latitudes, this coefficient is higher, in southern latitudes it is lower.

Light coefficient is the ratio of glass area in windows to floor area. In the classrooms and workshops of the school, it should be at least 1: 4, in the corridors and the gym - 1: 5, 1: 6, respectively, in auxiliary rooms - 1: 8, on landings - 1: 12.

The illumination of classrooms with natural light depends on the shape and size of the windows, their height, as well as on the external environment of the building (neighboring houses, green spaces).

Rounding the upper part of the window opening with one-sided lighting violates the ratio of the height of the window edge to the depth (width) of the room, which should be 1:2, i.e. the depth of the room should exceed twice the height from the floor to the upper edge of the window. In practice, this means: the higher the upper edge of the window, the more direct sunlight enters the room and the better the desks in the third row from the windows are lit.

To prevent the blinding effect of direct sunlight and overheating of the rooms, special visors are hung above the windows from the outside, and from the inside the room is shaded with light curtains. To prevent the blinding effect of reflected rays, it is not recommended to paint ceilings and walls with oil paints.

The color of the furniture also affects the illumination of the school premises, so the desks are painted in light colors or covered with light plastic. Dirty window panes and flowers on window sills reduce light. It is allowed to put flowers on window sills with a height (together with a flowerpot) of no more than 25-30 cm. Tall flowers are placed at the windows on stands, and so that their crown does not protrude above the window sill above 25-30 cm, or in piers on ladder stands or pots.

Artificial lighting. As sources of artificial lighting for school premises, incandescent lamps with a power of 250-350 W and fluorescent lamps of “white” light (SB type) with a power of 40 and 80 W are used. Fluorescent lamps of diffused light are suspended in rooms where the ceiling height is 3,3 m; for lower heights, ceiling lamps are used. All luminaires must be equipped with silent ballasts. The total power of fluorescent lamps in the classroom should be 1040 W, incandescent lamps - 2400 W, which is achieved by installing at least eight lamps of 130 W each for fluorescent lighting and eight lamps of 300 W each for incandescent lamps. Illumination rate (in watts) per 1 sq. m of classroom area (the so-called specific power) with fluorescent lamps is 21-22, with incandescent lamps - 42-48. The first corresponds to illumination of 300 lux, the second - 150 lux at the student’s workplace.

Mixed lighting (natural and artificial) does not affect the organs of vision. What can not be said about the simultaneous use of incandescent lamps and fluorescent lamps in the room, which have a different nature of the glow and color of the light flux.

5.5. auditory analyzer

The main function of the hearing organs is the perception of fluctuations in the air environment. The organs of hearing are closely connected with the organs of balance. The receptors of the auditory and vestibular systems are located in the inner ear.

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

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

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

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

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

The external auditory canal in an adult has a length of 2,5 cm, a capacity of 1 cu. see The skin lining the ear canal has fine hairs and modified sweat glands that produce earwax. They play a protective role. Earwax is made up of fat cells that contain pigment.

The outer and middle ear are separated by the tympanic membrane, which is a thin connective tissue plate. The thickness of the tympanic membrane is about 0,1 mm, on the outside it is covered with epithelium, and on the inside - with a mucous membrane. The tympanic membrane is located obliquely and begins to oscillate when sound waves hit it. Since the eardrum does not have its own period of oscillation, it fluctuates with any sound according to its wavelength.

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

The tympanic cavity is connected to the nasopharynx by means of an auditory (Eustachian) tube 3,5 cm long, very narrow (2 mm), maintaining the same pressure from the outside and inside on the tympanic membrane, thereby providing the most favorable conditions for its oscillation. The opening of the tube in the pharynx is most often in a collapsed state, and air passes into the tympanic cavity during the act of swallowing and yawning.

The inner ear is located in the stony part of the temporal bone and is a bony labyrinth, inside which there is a membranous labyrinth of connective tissue, which, as it were, is inserted into the bony labyrinth and repeats its shape. Between the bony and membranous labyrinths there is a fluid - perilymph, and inside the membranous labyrinth - endolymph. In addition to the oval window, there is a round window in the wall separating the middle ear from the inner ear, which makes it possible for the fluid to oscillate.

The bony labyrinth consists of three parts: in the center is the vestibule, in front of it is the cochlea, and behind it are the semicircular canals. Bone cochlea - a spirally meandering canal, forming two and a half turns around a conical rod. The diameter of the bone canal at the base of the cochlea is 0,04 mm, at the top - 0,5 mm. A bone spiral plate departs from the rod, which divides the canal cavity into two parts - stairs.

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

The inner hair cells are arranged in one row, there are 3,5 thousand of them along the entire length of the membranous canal. The outer hair cells are arranged in three to four rows, there are 12-20 thousand of them. Each receptor cell has an elongated shape, it has 60-70 the smallest hairs (4-5 microns long). The hairs of the receptor cells are washed by the endolymph and come into contact with the integumentary plate, which hangs over them. Hair cells are covered by nerve fibers of the cochlear branch of the auditory nerve. The second neuron of the auditory pathway is located in the medulla oblongata; then the path goes, crossing, to the posterior tubercles of the quadrigemina, and from them to the temporal region of the cortex, where the central part of the auditory analyzer is located.

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

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

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

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

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

Hearing acuity is determined by the smallest sound intensity that causes a sound sensation. This is the so-called threshold of hearing. In an adult, the hearing threshold is 10-12 dB, in children 6-9 years old it is 17-24 dB, in children 10-12 years old - 14-19 dB. The greatest hearing acuity is achieved by the age of 14-19.

5.6. vestibular apparatus

The vestibular apparatus is located in the inner ear and consists of semicircular canals located in three mutually perpendicular planes, and two sacs (oval and round) lying closer to the cochlea. On the inner surface of the sacs there are hair cells. They are located in a gelatinous mass, which contains a large number of calcareous crystals - otoliths.

In the extensions of the semicircular canals (ampullae) there is one crescent-shaped bone crest each. The membranous labyrinth and an accumulation of supporting and sensory receptors, which are equipped with hairs, adjoin the scallop. The semicircular canals are filled with endolymph.

The stimuli of the otolithic apparatus are accelerating or slowing down movement of the body, shaking, pitching and tilting the body or head to the side, causing pressure of the otoliths on the hairs of the receptor cells. The stimulus of the receptors of the semicircular canals is an accelerated or slow rotational movement in any plane. Impulses coming from the otolithic apparatus and semicircular canals make it possible to analyze the position of the head in space and changes in the speed and direction of movements. Increased irritation of the vestibular apparatus is accompanied by an increase or slowdown in contractions of the heart, respiration, vomiting, and increased sweating. With increased excitability of the vestibular apparatus in conditions of sea rolling, signs of "seasickness" occur, which are characterized by the above vegetative disorders. Similar changes are observed when flying, traveling by train and car.

Author: Antonova O.A.

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Random news from the Archive Found the reason for fluctuations in the brightness of the Sun 28.08.2017 In the new study, scientists have been able to show for the first time that fluctuations in the Sun's brightness are determined by two main factors: magnetic fields on the surface of our star and giant plasma streams rising to the surface from its depths. For the first time, researchers have been able to reproduce fluctuations in the Sun's brightness on all time scales observed to date, from minutes to decades. These new findings can also be applied to distant stars. They can simplify the search for exoplanets. When an exoplanet passes in front of a star, it briefly obscures part of the star's disk and makes the star less bright. Even from tens or hundreds of light-years away, space telescopes can detect these changes in the brightness of stars - and thus detect planets. However, this is just a theory. In practice, the search for exoplanets is complicated, first of all, by the fact that in addition to changes in brightness associated with the passage of planets, stars also experience brightness fluctuations not associated with planets, the same as our Sun experiences. In their work, astronomers led by Alexander Shapiro from the Max Planck Institute for Solar System Research, Germany, propose a model that describes the fluctuations in the brightness of the Sun using only two phenomena to explain: convective plasma flows rising from the depths of a star and magnetic fields near its surface. The first mechanism is that hotter, brighter masses of matter rise to the surface of the Sun, and zones of increased brightness form at their exits to the surface, while colder masses that have already been on the surface for a long time are dimmer. . The second factor is associated with the magnetic activity of the star's surface and manifests itself in the fact that during the period of increased magnetic activity, large dark zones - spots appear on the surface. The joint action of these two factors explains all changes in the brightness of the Sun observed today on all time scales, the authors of the model emphasize.

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