vision analyzer. The visual analyzer, its structure and functions, the organ of vision. Protective eye systems

visual analyzer. It is represented by the perceiving department - the receptors of the retina, the optic nerves, the conduction system and the corresponding areas of the cortex in the occipital lobes of the brain.

Eyeball(see figure) has a spherical shape, enclosed in the orbit. The auxiliary apparatus of the eye is represented by eye muscles, fatty tissue, eyelids, eyelashes, eyebrows, lacrimal glands. The mobility of the eye is provided by striated muscles, which at one end are attached to the bones of the orbital cavity, the other - to the outer surface of the eyeball - the albuginea. Two folds of skin surround the front of the eyes - eyelids. Their inner surfaces are covered with a mucous membrane - conjunctiva. The lacrimal apparatus consists of lacrimal glands and outflow tracts. A tear protects the cornea from hypothermia, drying out and washes away settled dust particles.

The eyeball has three shells: outer - fibrous, middle - vascular, inner - mesh. fibrous sheath opaque and is called protein or sclera. In front of the eyeball, it passes into a convex transparent cornea. Middle shell supplied with blood vessels and pigment cells. In the anterior part of the eye, it thickens, forming the ciliary body, in the thickness of which is the ciliary muscle, which changes the curvature of the lens with its contraction. The ciliary body passes into the iris, consisting of several layers. Pigment cells lie in a deeper layer. Eye color depends on the amount of pigment. There is a hole in the center of the iris - pupil, around which the circular muscles are located. When they contract, the pupil narrows. The radial muscles in the iris dilate the pupil. The innermost layer of the eye retina, containing rods and cones - light-sensitive receptors representing the peripheral part of the visual analyzer. There are about 130 million rods and 7 million cones in the human eye. More cones are concentrated in the center of the retina, and rods are located around them and on the periphery. Nerve fibers depart from the photosensitive elements of the eye (rods and cones), which, connecting through intermediate neurons, form optic nerve. There are no receptors at the site of its exit from the eye, this area is not sensitive to light and is called blind spot. Outside of the blind spot, only cones are concentrated on the retina. This area is called yellow spot, it has the largest number of cones. The posterior retina is the bottom of the eyeball.

Behind the iris is a transparent body that has the shape of a biconvex lens - lens, able to refract light rays. The lens is enclosed in a capsule from which the ligaments of zinn extend and attach to the ciliary muscle. When the muscles contract, the ligaments relax and the curvature of the lens increases, it becomes more convex. The cavity of the eye behind the lens is filled with a viscous substance - vitreous body.

The emergence of visual sensations. Light stimuli are perceived by the rods and cones of the retina. Before reaching the retina, light rays pass through the refractive media of the eye. In this case, a real inverse reduced image is obtained on the retina. Despite the inverted image of objects on the retina, due to the processing of information in the cerebral cortex, a person perceives them in their natural position, moreover, visual sensations are always supplemented and consistent with the readings of other analyzers.

The ability of the lens to change its curvature depending on the distance of the object is called accommodation. It increases when viewing objects at a close distance and decreases when the object is removed.

Eye dysfunctions include farsightedness And myopia. With age, the elasticity of the lens decreases, it becomes more flattened and accommodation weakens. At this time, a person sees well only distant objects: the so-called senile farsightedness develops. Congenital farsightedness is associated with a reduced size of the eyeball or a weak refractive power of the cornea or lens. In this case, the image from distant objects is focused behind the retina. When wearing glasses with convex lenses, the image moves to the retina. Unlike senile, with congenital farsightedness, the accommodation of the lens can be normal.

With myopia, the eyeball is enlarged in size, the image of distant objects, even in the absence of accommodation of the lens, is obtained in front of the retina. Such an eye clearly sees only close objects and is therefore called myopic. Glasses with concave glasses, moving the image to the retina, correct myopia.

receptors in the retina sticks and cones - differ in both structure and function. Cones are associated with daytime vision, they are excited in bright light, and twilight vision is associated with rods, since they are excited in low light. The sticks contain a red substance - visual Purple, or rhodopsin; in the light, as a result of a photochemical reaction, it decomposes, and in the dark it is restored within 30 minutes from the products of its own cleavage. That is why a person, entering a dark room, at first sees nothing, and after a while begins to gradually distinguish objects (by the time the synthesis of rhodopsin is completed). Vitamin A is involved in the formation of rhodopsin, with its deficiency, this process is disrupted and develops. "night blindness". The ability of the eye to see objects in different light levels is called adaptation. It is disturbed with a lack of vitamin A and oxygen, as well as with fatigue.

Cones contain another light-sensitive substance - iodopsin. It disintegrates in the dark and is restored in the light within 3-5 minutes. The breakdown of iodopsin in the presence of light gives color sensation. Of the two retinal receptors, only cones are sensitive to color, of which there are three types in the retina: some perceive red, others green, and others blue. Depending on the degree of excitation of the cones and the combination of stimuli, various other colors and their shades are perceived.

The eye should be protected from various mechanical influences, read in a well-lit room, holding the book at a certain distance (up to 33-35 cm from the eye). The light should fall on the left. You can not lean close to the book, since the lens in this position is in a convex state for a long time, which can lead to the development of myopia. Too bright lighting harms vision, destroys light-perceiving cells. Therefore, steelworkers, welders and other similar professions are advised to wear dark protective goggles while working. You can not read in a moving vehicle. Due to the instability of the position of the book, the focal length changes all the time. This leads to a change in the curvature of the lens, a decrease in its elasticity, as a result of which the ciliary muscle weakens. Visual impairment can also occur due to a lack of vitamin A.

Briefly:

The main part of the eye is the eyeball. It consists of the lens, vitreous body and aqueous humor. The lens has the appearance of a biconcave lens. It has the ability to change its curvature depending on the distance of the object. Its curvature is changed by the ciliary muscle. The function of the vitreous body is to maintain the shape of the eye. There are also two types of aqueous humor: anterior and posterior. The anterior is between the cornea and the iris, and the posterior is between the iris and the lens. The function of the lacrimal apparatus is to moisten the eye. Myopia is a vision disorder in which an image forms in front of the retina. Farsightedness is a pathology in which the image is formed behind the retina. The image is formed inverted, reduced.

The meaning of vision Thanks to the eyes, we get 85% of the information about the world around us, they, according to I.M. Sechenov, give a person up to 1000 sensations per minute. The eye allows you to see objects, their shape, size, color, movement. The eye is able to distinguish a well-lit object with a diameter of one tenth of a millimeter at a distance of 25 centimeters. But if the object itself glows, it can be much smaller. Theoretically, a person could see the flame of a candle at a distance of 200 km. The eye is able to distinguish between pure color tones and 5-10 million mixed shades. Full adaptation of the eye to the dark takes minutes.

Scheme of the structure of the eye Fig.1. Scheme of the structure of the eye 1 - sclera, 2 - choroid, 3 - retina, 4 - cornea, 5 - iris, 6 - ciliary muscle, 7 - lens, 8 - vitreous body, 9 - optic disc, 10 - optic nerve, 11 - yellow spot.

The ground substance of the cornea consists of a transparent connective tissue stroma and corneal bodies. Anteriorly, the cornea is covered with stratified epithelium. The cornea (cornea) is the anterior most convex transparent part of the eyeball, one of the refractive media of the eye.

The iris (iris) is a thin movable diaphragm of the eye with a hole (pupil) in the center; located behind the cornea, in front of the lens. The iris contains a different amount of pigment, on which its color "eye color" depends. The pupil is a round hole through which light rays penetrate and reach the retina (the size of the pupil varies [depending on the intensity of the light flux: in bright light it is narrower, in weak light and wider in the dark].

The lens is a transparent body located inside the eyeball opposite the pupil; Being a biological lens, the lens is an important part of the refractive apparatus of the eye. The lens is a transparent biconvex rounded elastic formation,

Photoreceptors signs of rod cones Length 0.06 mm 0.035 mm Diameter 0.002 mm 0.006 mm Number 125 - 130 million 6 - 7 million. - accumulation of cones, Blind spot - exit point of the optic nerve (no receptors)

The structure of the retina: Anatomically, the retina is a thin shell, adjacent throughout its entire length from the inside to the vitreous body, and from the outside to the choroid of the eyeball. Two parts are distinguished in it: the visual part (the receptive field is the area with photoreceptor cells (rods or cones) and the blind part (the area on the retina that is not sensitive to light). Light falls from the left and passes through all layers, reaching photoreceptors (cones and rods ) Which transmit the signal along the optic nerve to the brain.

Myopia Nearsightedness (myopia) is a defect (anomaly of refraction) in which the image does not fall on the retina, but in front of it. The most common cause is an enlarged (relative to normal) length of the eyeball. A rarer option is when the refractive system of the eye focuses the rays more than necessary (and, as a result, they again converge not on the retina, but in front of it). In any of the options, when viewing distant objects, a fuzzy, blurry image appears on the retina. Myopia most often develops during school years, as well as while studying at secondary and higher educational institutions, and is associated with prolonged visual work at close range (reading, writing, drawing), especially with improper lighting and poor hygienic conditions. With the introduction of computer science in schools and the spread of personal computers, the situation has become even more serious.

Farsightedness (hypermetropia) is a feature of refraction of the eye, consisting in the fact that images of distant objects at rest of accommodation are focused behind the retina. At a young age, with not too high farsightedness, with the help of accommodation tension, the image can be focused on the retina. One of the causes of farsightedness may be the reduced size of the eyeball on the anterior-posterior axis. Almost all babies are farsighted. But with age, for most, this defect disappears due to the growth of the eyeball. The cause of age-related (senile) farsightedness (presbyopia) is a decrease in the ability of the lens to change curvature. This process begins at the age of about 25 years, but only by 4050 years leads to a decrease in visual acuity when reading at a normal distance from the eyes (2530 cm). Color blindness Up to 14 months in newborn girls and up to 16 months in boys, there is a period of complete non-perception of colors. The formation of color perception ends by 7.5 years in girls and by 8 years in boys. About 10% of men and less than 1% of women have a color vision defect (indistinguishability of red and green or, less commonly, blue; there may be complete indistinguishability of colors)

The concept of the analyzer

It is represented by the perceiving department - the receptors of the retina, the optic nerves, the conduction system and the corresponding areas of the cortex in the occipital lobes of the brain.

A person sees not with his eyes, but through his eyes, from where information is transmitted through the optic nerve, chiasm, visual tracts to certain areas of the occipital lobes of the cerebral cortex, where the picture of the external world that we see is formed. All these organs make up our visual analyzer or visual system.

The presence of two eyes allows us to make our vision stereoscopic (that is, to form a three-dimensional image). The right side of the retina of each eye transmits through the optic nerve the "right side" of the image to the right side of the brain, the left side of the retina does the same. Then the two parts of the image - right and left - the brain connects together.

Since each eye perceives "its own" picture, if the joint movement of the right and left eyes is disturbed, binocular vision may be disturbed. Simply put, you will begin to see double, or you will see two completely different pictures at the same time.

The structure of the eye

The eye can be called a complex optical device. Its main task is to "transmit" the correct image to the optic nerve.

Main functions of the eye:

an optical system that projects an image;

a system that perceives and "encodes" the received information for the brain;

· "Serving" life support system.

The cornea is the transparent membrane that covers the front of the eye. There are no blood vessels in it, it has a large refractive power. Included in the optical system of the eye. The cornea borders on the opaque outer shell of the eye - the sclera.

The anterior chamber of the eye is the space between the cornea and the iris. It is filled with intraocular fluid.

The iris is shaped like a circle with a hole inside (the pupil). The iris consists of muscles, with the contraction and relaxation of which the size of the pupil changes. It enters the choroid of the eye. The iris is responsible for the color of the eyes (if it is blue, it means that there are few pigment cells in it, if it is brown, there are many). It performs the same function as the aperture in a camera, adjusting the light output.

The pupil is a hole in the iris. Its dimensions usually depend on the level of illumination. The more light, the smaller the pupil.

The lens is the "natural lens" of the eye. It is transparent, elastic - it can change its shape, "focusing" almost instantly, due to which a person sees well both near and far. It is located in the capsule, held by the ciliary girdle. The lens, like the cornea, is part of the optical system of the eye.

The vitreous body is a gel-like transparent substance located in the back of the eye. The vitreous body maintains the shape of the eyeball and is involved in intraocular metabolism. Included in the optical system of the eye.

The retina - consists of photoreceptors (they are sensitive to light) and nerve cells. Receptor cells located in the retina are divided into two types: cones and rods. In these cells, which produce the enzyme rhodopsin, the energy of light (photons) is converted into electrical energy of the nervous tissue, i.e. photochemical reaction.

The rods are highly sensitive to light and allow you to see in low light, they are also responsible for peripheral vision. Cones, on the contrary, require more light for their work, but it is they that allow you to see fine details (are responsible for central vision), make it possible to distinguish colors. The greatest concentration of cones is in the fovea (macula), which is responsible for the highest visual acuity. The retina is adjacent to the choroid, but loosely in many areas. It is here that it tends to flake off in various diseases of the retina.

Sclera - an opaque outer shell of the eyeball, passing in front of the eyeball into a transparent cornea. 6 oculomotor muscles are attached to the sclera. It contains a small number of nerve endings and blood vessels.

The choroid - lines the posterior sclera, adjacent to the retina, with which it is closely connected. The choroid is responsible for the blood supply to the intraocular structures. In diseases of the retina, it is very often involved in the pathological process. There are no nerve endings in the choroid, therefore, when it is ill, pain does not occur, usually signaling some kind of malfunction.

Optic nerve - with the help of the optic nerve, signals from nerve endings are transmitted to the brain.

1. What is an analyzer? How is it arranged?

An analyzer is a system that provides perception, delivery to the brain and analysis of any type of information in it (visual, auditory, olfactory, and others).

All analyzers consist of 3 main parts:

Receptor (peripheral section): receptors perceive irritation and convert the energy of the stimulus (light, sound, temperature) into nerve impulses.

Conducting nerve pathways (conduction department)

Central department: nerve centers in certain areas of the cerebral cortex, in which the transformation of a nerve impulse into a specific sensation is carried out.

2. What are the peripheral, conductive and central parts of the visual analyzer?

Peripheral: rods and cones of the retina. The conduction department: the optic nerve, the superior colliculus of the quadrigemina (midbrain) and the optic nuclei of the thalamus. Central department: visual zone of the cerebral cortex (occipital region).

3. List the structures of the auxiliary apparatus of the eye and their functions.

The auxiliary apparatus of the eye includes eyebrows and eyelashes, eyelids, lacrimal gland, lacrimal canaliculi, oculomotor muscles, nerves and blood vessels. Eyebrows wick away sweat from the forehead, and eyebrows and eyelashes protect the eyes from dust. The lacrimal gland produces tear fluid, which, when blinked, moistens, disinfects and cleanses the eye. Excess fluid collects in the corner of the eye and is discharged through the lacrimal ducts into the nasal cavity. The eyelids protect the eye from light rays, dust; blinking (periodic closing and opening of the eyelids) ensures a uniform distribution of tear fluid over the surface of the eyeball. Thanks to the oculomotor muscles, we can follow moving objects without turning our heads. Vessels provide nutrition to the eye and its supporting structures.

4. How is the eyeball arranged?

The eyeball has the shape of a ball and is located in a special recess of the skull - the eye socket. The wall of the eyeball consists of three membranes: outer fibrous, middle vascular and retina. The cavity of the eyeball is filled with a colorless and transparent vitreous body. The fibrous membrane is the outer protein shell of the eye, completely covering it and serving to protect the rest of the eye. In it, the posterior opaque part is distinguished - the albuginea (sclera) and the anterior transparent part - the cornea. The cornea is convex forward, it has no blood vessels and the greatest refraction of light rays occurs in it. The choroid is located under the fibrous one, the choroid itself is distinguished in it (it lies under the sclera, is penetrated by many blood vessels and provides nutrition to the eye), the ciliary body, and the iris. The cells of the iris contain melanin, which determines the color of the eyes. In the center of the iris is a small hole - the pupil, which can expand or contract depending on the amount of light entering the eye or on the influence of the sympathetic and parasympathetic nervous systems. Directly behind the pupil lies the lens (a transparent biconvex formation with a diameter of up to 1 cm). The inner shell of the eye is the retina, which consists of receptors (rods and cones) and nerve cells that connect all receptors into a single network and transmit information to the optic nerve. Most of the cones are located in the retina opposite the pupil, in the macula (the place of best vision). Near the yellow spot, at the exit of the optic nerve, there is an area of ​​​​the retina devoid of receptors - a blind spot.

5. What is the importance of the ability of the lens to change its curvature?

Due to changes in the curvature of the lens, the image in the eye is clearly focused on the surface of the retina at one point, which can be compared to focusing on a camera.

6. What is the function of the pupil?

The pupil regulates the amount of light entering the eye. The expansion of the pupil in low light and its narrowing in bright light is called the accommodative ability of the eye.

7. Where are rods and cones located, what are their similarities and differences?

Rods and cones are located in the retina. Both rods and cones are photoreceptors, lie in a single layer and contain specific proteins, the molecules of which are excited by light. They differ in shape and degree of sensitivity to light and color. Cones are photoreceptors that perceive the outlines and details of objects and provide color vision. According to the three-component theory of light, there are three types of cones, each of which perceives a certain color better: red-orange, yellow-green, blue-violet. Rods are photoreceptors that provide black and white vision and are highly sensitive to light. Cones are less sensitive to light than rods. Therefore, at dusk, vision is provided only by rods, because of which, under these conditions, a person does not distinguish colors well.

8. In what part of the eye are the receptors that perceive light and convert it into a nerve impulse?

Photoreceptors (rods and cones) are found in the retina.

9. Where is the blind spot located?

Near the yellow spot, at the exit of the optic nerve, there is an area of ​​​​the retina devoid of receptors - a blind spot.

10. In what part of the retina is the clearest color image formed? What is it connected with?

The clearest image of objects is formed in the macula, the area in the central part of the retina, in which the cones are located with the maximum density, and the rods are absent. Light rays are projected onto the macula from the point at which our gaze is directed.

11. Describe the work of the visual analyzer from the receipt of light on the organ of vision to the formation of a visual image in the brain.

Light enters the eyeball, the oculomotor muscles provide its optimal position. Light passes through the transparent cornea and pupil and hits the lens. The lens ensures that the image is focused on the retina after passing through the transparent vitreous body. On the retina, the image is reduced and inverted. Light on the retina causes excitation of photoreceptors and the conversion of light into nerve impulses. Nerve impulses are transmitted to the brain through the optic nerve. The optic nerves enter the skull through special openings and converge together, and then the inner parts of the nerve cross and diverge again, forming the optic tracts. As a result, everything that we see on the right is in the left visual tract, and what is on the left is in the right. The optic tracts end in the superior colliculus of the midbrain and the thalamic optic tracts, where information is further processed. The final processing of information takes place in the visual zones of the occipital lobes of both hemispheres, where the image is again turned “from head to foot”.

12. What is the reason for such visual impairments as nearsightedness and farsightedness? What processes are corrected by spectacle lenses? Tell us about the prevention of these diseases.

Myopia is a visual impairment in which an image is formed in front of the retina. A nearsighted person sees clearly only nearby objects. Farsightedness is a visual impairment in which an image is formed in front of the retina. A person with such a pathology sees objects located at a distance better. The causes of such pathologies are congenital and acquired. Congenital include congenital elongated (nearsightedness) or shortened (farsightedness) eyeball. Acquired include an increase in the curvature of the lens or weakening of the ciliary muscle (nearsightedness); compaction of the lens, leading to a loss of its elasticity and a decrease in curvature (farsightedness, more common in the elderly). Spectacle lenses create additional scattering of light in case of farsightedness or a larger angle of refraction in case of myopia.

Prevention of these diseases consists in observing a certain hygiene of vision. This includes visual gymnastics when eyes are tired, reading and writing in sufficient light, so that for right-handers the light falls on the left, and for left-handers on the right. The distance from the eye to the object should be 30-35 cm; after every 30-40 minutes of working at the computer, you need to take 10-15 minutes breaks, when watching TV, the distance to it should be at least 2.5-3 m and the viewing time should not exceed 30-40 minutes a day. In the evening, when working at a computer or watching TV, you need to turn on the lighting.

13. Why is it said that the eye looks and the brain sees?

The eye is only a peripheral part of the visual analyzer, while image processing takes place in the cerebral cortex. With injuries of the occipital lobe, a person stops seeing, that is, an image is formed on the retina of the eye, he looks, as it were, but does not recognize and does not recognize objects, he does not see them.

To interact with the outside world, a person needs to receive and analyze information from the external environment. For this, nature endowed him with sense organs. There are six of them: eyes, ears, tongue, nose, skin and Thus, a person forms an idea about everything that surrounds him and about himself as a result of visual, auditory, olfactory, tactile, gustatory and kinesthetic sensations.

It can hardly be argued that any sense organ is more significant than the others. They complement each other, creating a complete picture of the world. But what is most of all the information - up to 90%! - people perceive with the help of the eyes - this is a fact. To understand how this information enters the brain and how it is analyzed, you need to understand the structure and functions of the visual analyzer.

Features of the visual analyzer

Thanks to visual perception, we learn about the size, shape, color, relative position of objects in the surrounding world, their movement or immobility. This is a complex and multi-stage process. The structure and functions of the visual analyzer - a system that receives and processes visual information, and thereby provides vision - are very complex. Initially, it can be divided into peripheral (perceiving the initial data), conducting and analyzing parts. Information is received through the receptor apparatus, which includes the eyeball and auxiliary systems, and then it is sent using the optic nerves to the corresponding centers of the brain, where it is processed and visual images are formed. All departments of the visual analyzer will be discussed in the article.

How is the eye. Outer layer of the eyeball

The eyes are a paired organ. Each eyeball is shaped like a slightly flattened ball and consists of several shells: external, middle and internal, surrounding the fluid-filled cavities of the eye.

The outer shell is a dense fibrous capsule that retains the shape of the eye and protects its internal structures. In addition, six motor muscles of the eyeball are attached to it. The outer shell consists of a transparent front part - the cornea, and a back, opaque - sclera.

The cornea is the refractive medium of the eye, it is convex, looks like a lens and consists, in turn, of several layers. There are no blood vessels in it, but there are many nerve endings. The white or bluish sclera, the visible part of which is commonly referred to as the white of the eye, is formed from connective tissue. Muscles are attached to it, providing turns of the eyes.

Middle layer of the eyeball

The middle choroid is involved in metabolic processes, providing nutrition to the eye and the removal of metabolic products. The front, most noticeable part of it is the iris. The pigment substance in the iris, or rather, its quantity, determines the individual shade of a person's eyes: from blue, if there is not enough of it, to brown, if enough. If the pigment is absent, as happens with albinism, then the plexus of vessels becomes visible, and the iris becomes red.

The iris is located just behind the cornea and is based on muscles. The pupil - a rounded hole in the center of the iris - thanks to these muscles regulates the penetration of light into the eye, expanding in low light and narrowing in too bright. The continuation of the iris is the function of this part of the visual analyzer is the production of fluid that nourishes those parts of the eye that do not have their own vessels. In addition, the ciliary body has a direct influence on the thickness of the lens through special ligaments.

In the posterior part of the eye, in the middle layer, there is the choroid, or the vascular proper, almost entirely consisting of blood vessels of different diameters.

Retina

The inner, thinnest layer is the retina, or retina, formed by nerve cells. Here there is a direct perception and primary analysis of visual information. The back of the retina is made up of specialized photoreceptors called cones (7 million) and rods (130 million). They are responsible for the perception of objects by the eye.

Cones are responsible for color recognition and provide central vision, allowing you to see the smallest details. Rods, being more sensitive, enable a person to see in black and white colors in poor lighting conditions, and are also responsible for peripheral vision. Most of the cones are concentrated in the so-called macula opposite the pupil, slightly above the entrance of the optic nerve. This place corresponds to the maximum visual acuity. The retina, as well as all parts of the visual analyzer, has a complex structure - 10 layers are distinguished in its structure.

The structure of the eye cavity

The ocular nucleus consists of the lens, the vitreous body and chambers filled with fluid. The lens looks like a convex transparent lens on both sides. It has neither vessels nor nerve endings and is suspended from the processes of the ciliary body surrounding it, the muscles of which change its curvature. This ability is called accommodation and helps the eye to focus on close or, conversely, distant objects.

Behind the lens, adjacent to it and further to the entire surface of the retina, is located This is a transparent gelatinous substance that fills most of the volume. This gel-like mass contains 98% water. The purpose of this substance is to conduct light rays, compensate for intraocular pressure drops, and maintain the constancy of the shape of the eyeball.

The anterior chamber of the eye is limited by the cornea and iris. It connects through the pupil to a narrower posterior chamber extending from the iris to the lens. Both cavities are filled with intraocular fluid, which freely circulates between them.

Light refraction

The system of the visual analyzer is such that initially the light rays are refracted and focused on the cornea and pass through the anterior chamber to the iris. Through the pupil, the central part of the light flux enters the lens, where it is more accurately focused, and then through the vitreous to the retina. An image of an object is projected on the retina in a reduced and, moreover, inverted form, and the energy of light rays is converted by photoreceptors into nerve impulses. The information then travels to the brain via the optic nerve. The place on the retina through which the optic nerve passes is devoid of photoreceptors, therefore it is called the blind spot.

The motor apparatus of the organ of vision

The eye, in order to respond in a timely manner to stimuli, must be mobile. Three pairs of oculomotor muscles are responsible for the movement of the visual apparatus: two pairs of straight and one oblique. These muscles are perhaps the fastest-acting in the human body. The oculomotor nerve controls the movement of the eyeball. It connects with four of the six eye muscles, ensuring their adequate work and coordinated eye movements. If for some reason the oculomotor nerve ceases to function normally, this is expressed in various symptoms: strabismus, drooping of the eyelid, doubling of objects, pupil dilation, disturbances of accommodation, protrusion of the eyes.

Protective eye systems

Continuing such a voluminous topic as the structure and functions of the visual analyzer, one cannot fail to mention those systems that protect it. The eyeball is located in the bone cavity - the eye socket, on a shock-absorbing fatty pad, where it is reliably protected from impact.

In addition to the orbit, the protective apparatus of the organ of vision includes the upper and lower eyelids with eyelashes. They protect the eyes from the ingress of various objects from the outside. In addition, the eyelids help to evenly distribute tear fluid over the surface of the eye, remove the smallest dust particles from the cornea when blinking. Eyebrows also perform protective functions to some extent, protecting the eyes from sweat flowing from the forehead.

The lacrimal glands are located in the upper outer corner of the orbit. Their secret protects, nourishes and moisturizes the cornea, and also has a disinfecting effect. Excess fluid drains through the tear duct into the nasal cavity.

Further processing and final processing of information

The conduction section of the analyzer consists of a pair of optic nerves that exit the eye sockets and enter special canals in the cranial cavity, further forming an incomplete decussation, or chiasma. Images from the temporal (outer) part of the retina remain on the same side, while images from the inner, nasal part are crossed and transmitted to the opposite side of the brain. As a result, it turns out that the right visual fields are processed by the left hemisphere, and the left - by the right. Such an intersection is necessary for the formation of a three-dimensional visual image.

After decussation, the nerves of the conduction section continue in the optic tracts. Visual information enters the part of the cerebral cortex that is responsible for its processing. This zone is located in the occipital region. There, the final transformation of the received information into a visual sensation takes place. This is the central part of the visual analyzer.

So, the structure and functions of the visual analyzer are such that disturbances in any of its sections, whether it be the perceiving, conducting or analyzing zones, entail a failure of its work as a whole. This is a very multifaceted, subtle and perfect system.

Violations of the visual analyzer - congenital or acquired - in turn, lead to significant difficulties in the knowledge of reality and limited opportunities.