The eyes, the organ of vision, can be compared to a window into the world. We receive approximately 70% of all information through vision, for example about the shape, size, color of objects, distance to them, etc. The visual analyzer controls motor and labor activity person; Thanks to vision, we can use books and computer screens to study the experience accumulated by humanity.

The organ of vision consists of the eyeball and an auxiliary apparatus. Accessory apparatus - eyebrows, eyelids and eyelashes, lacrimal gland, lacrimal canaliculi, oculomotor muscles, nerves and blood vessels

Eyebrows and eyelashes protect your eyes from dust. In addition, eyebrows drain sweat from the forehead. Everyone knows that a person blinks constantly (2-5 eyelid movements per minute). But do they know why? It turns out that at the moment of blinking, the surface of the eye is moistened with tear fluid, which protects it from drying out, while at the same time being cleansed of dust. Tear fluid is produced by the lacrimal gland. It contains 99% water and 1% salt. Up to 1 g of tear fluid is secreted per day, it collects in the inner corner of the eye, and then enters the lacrimal canaliculi, which discharge it into the nasal cavity. If a person cries, the tear fluid does not have time to escape through the canaliculi into the nasal cavity. Then tears flow through the lower eyelid and run down the face in drops.

The eyeball is located in the recess of the skull - the orbit. It has a spherical shape and consists of inner core, covered with three membranes: the outer - fibrous, the middle - vascular and the inner - reticular. The fibrous membrane is divided into a posterior opaque part - the tunica albuginea, or sclera, and an anterior transparent part - the cornea. The cornea is a convex-concave lens through which light enters the eye. The choroid is located under the sclera. Its front part is called the iris, and it contains the pigment that determines the color of the eyes. In the center of the iris there is a small hole - the pupil, which reflexively, with the help of smooth muscles, can expand or contract, allowing the required amount of light into the eye.

The choroid itself is penetrated by a dense network of blood vessels that supply the eyeball. From inside to choroid There is an adjacent layer of pigment cells that absorb light, so light is not scattered or reflected inside the eyeball.

Directly behind the pupil is a biconvex transparent lens. It can reflexively change its curvature, providing a clear image on the retina - the inner layer of the eye. The retina contains receptors: rods (twilight light receptors that distinguish light from dark) and cones (they have less light sensitivity, but distinguish colors). Most cones are located on the retina opposite the pupil, in the macula. Next to this spot is where the optic nerve exits; there are no receptors here, which is why it is called the blind spot.

The inside of the eye is filled with a transparent and colorless vitreous humor.

Perception of visual stimuli. Light enters the eyeball through the pupil. Lens and vitreous serve to conduct and focus light rays onto the retina. Six oculomotor muscles ensure that the eyeball is positioned so that the image of an object falls exactly on the retina, on its macula.

In the retinal receptors, light is converted into nerve impulses, which are transmitted along the optic nerve to the brain through the nuclei of the midbrain (superior colliculus) and diencephalon (visual nuclei of the thalamus) - to the visual zone of the cerebral cortex, located in the occipital region. The perception of color, shape, illumination of an object, and its details, which begins in the retina, ends with analysis in the visual cortex. Here all the information is collected, deciphered and summarized. As a result, an idea of ​​the subject is formed.

Visual impairment. People's vision changes with age, as the lens loses elasticity and the ability to change its curvature. In this case, the image of closely located objects blurs - farsightedness develops. Another vision defect is myopia, when people, on the contrary, have difficulty seeing distant objects; it develops after prolonged stress and improper lighting. Myopia often occurs in school-age children due to improper working hours and poor lighting in the workplace. With myopia, the image of an object is focused in front of the retina, and with farsightedness, it is focused behind the retina and is therefore perceived as blurry. These visual defects can also be caused by congenital changes in the eyeball.

Myopia and farsightedness are corrected with specially selected glasses or lenses.

• The human visual analyzer has amazing sensitivity. Thus, we can distinguish a hole in the wall illuminated from the inside with a diameter of only 0.003 mm. A trained person (and women are much better at this) can distinguish hundreds of thousands of color shades. The visual analyzer only needs 0.05 seconds to recognize an object that comes into the field of view.

Test your knowledge

1. What is an analyzer?
2. How does the analyzer work?
3. Name the functions of the auxiliary apparatus of the eye.
4. How does the eyeball work?
5. What functions do the pupil and lens perform?
6. Where are the rods and cones located, what are their functions?
7. How does the visual analyzer work?
8. What is a blind spot?
9. How do myopia and farsightedness occur?
10. What are the causes of visual impairment?

Think

Why do they say that the eye looks, but the brain sees?

The organ of vision is formed by the eyeball and auxiliary apparatus. The eyeball can move thanks to six extraocular muscles. The pupil is a small hole through which light enters the eye. The cornea and lens are the refractive apparatus of the eye. Receptors (light-sensitive cells - rods, cones) are located in the retina.

The visual analyzer includes:

peripheral: retinal receptors;

conduction section: optic nerve;

central section: occipital lobe of the cerebral cortex.

Visual analyzer function: perception, conduction and decoding of visual signals.

Structures of the eye

The eye consists of eyeball And auxiliary apparatus.

Accessory eye apparatus

brows- protection from sweat;

eyelashes- protection from dust;

eyelids- mechanical protection and moisture maintenance;

lacrimal glands- located at the upper part of the outer edge of the orbit. It secretes tear fluid that moisturizes, washes and disinfects the eye. Excess tear fluid is removed into the nasal cavity through tear duct located in the inner corner of the orbit .

Eyeball

The eyeball is roughly spherical in shape with a diameter of about 2.5 cm.

It is located on the fat pad in the anterior part of the orbit.

The eye has three membranes:

tunica albuginea (sclera) with transparent cornea- outer very dense fibrous membrane of the eye;

choroid with outer iris and ciliary body- permeated blood vessels(nutrition of the eye) and contains a pigment that prevents the scattering of light through the sclera;

retina (retina) - the inner shell of the eyeball - the receptor part of the visual analyzer; function: direct perception of light and transmission of information to the central nervous system.

Conjunctiva- mucous membrane connecting the eyeball to the skin.

Tunica albuginea (sclera)- durable outer shell of the eye; the inner part of the sclera is impenetrable to set rays. Function: eye protection from external influences and light insulation;

Cornea- anterior transparent part of the sclera; is the first lens on the path of light rays. Function: mechanical protection of the eye and transmission of light rays.

Lens- a biconvex lens located behind the cornea. Function of the lens: focusing light rays. The lens has no blood vessels or nerves. It does not develop inflammatory processes. It contains many proteins, which can sometimes lose their transparency, leading to a disease called cataract.

Choroid- the middle layer of the eye, rich in blood vessels and pigment.

Iris- anterior pigmented part of the choroid; contains pigments melanin And lipofuscin, determining eye color.

Pupil- a round hole in the iris. Function: regulation of light flow entering the eye. The diameter of the pupil involuntarily changes with the help of the smooth muscles of the iris when the light changes.

Front and rear cameras- space in front and behind the iris filled with clear liquid ( aqueous humor).

Ciliary (ciliary) body- part of the middle (choroid) membrane of the eye; function: fixation of the lens, ensuring the process of accommodation (change in curvature) of the lens; production of aqueous humor in the chambers of the eye, thermoregulation.

Vitreous body- the cavity of the eye between the lens and the fundus of the eye, filled with a transparent viscous gel that maintains the shape of the eye.

Retina (retina)- receptor apparatus of the eye.

Structure of the retina

The retina is formed by the branches of the endings of the optic nerve, which, approaching the eyeball, passes through the tunica albuginea, and the sheath of the nerve merges with the tunica albuginea of ​​the eye. Inside the eye, the nerve fibers are distributed in the form of a thin retina that lines the posterior 2/3 inner surface eyeball.

The retina consists of supporting cells that form mesh structure, which is where its name comes from. Only its back part perceives light rays. The retina, in its development and function, is a part nervous system. However, the remaining parts of the eyeball play a supporting role in the retina’s perception of visual stimuli.

Retina- this is the part of the brain that is pushed outward, closer to the surface of the body, and maintains a connection with it through a pair of optic nerves.

Nerve cells form chains in the retina consisting of three neurons (see figure below):

the first neurons have dendrites in the form of rods and cones; these neurons are the terminal cells of the optic nerve; they perceive visual stimuli and are light receptors.

the second - bipolar neurons;

the third are multipolar neurons ( ganglion cells); Axons extend from them, which stretch along the bottom of the eye and form the optic nerve.

Photosensitive elements of the retina:

sticks- perceive brightness;

cones- perceive color.

The cones are excited slowly and only by bright light. They are able to perceive color. There are three types of cones in the retina. The first perceive the color red, the second - green, the third - blue. Depending on the degree of excitation of the cones and the combination of irritations, the eye perceives different colors and shades.

The rods and cones in the retina of the eye are mixed together, but in some places they are very densely located, in others they are rare or absent altogether. For each nerve fiber there are approximately 8 cones and about 130 rods.

In area macular spot There are no rods on the retina - only cones; here the eye has the greatest visual acuity and the best color perception. Therefore, the eyeball is in continuous motion, so that the part of the object being examined falls on the macula. As you move away from the macula, the density of the rods increases, but then decreases.

In low light, only rods are involved in the vision process (twilight vision), and the eye does not distinguish colors, vision turns out to be achromatic (colorless).

Nerve fibers extend from the rods and cones, which unite to form the optic nerve. The place where the optic nerve exits the retina is called optic disc. There are no photosensitive elements in the area of ​​the optic nerve head. Therefore, this place does not give a visual sensation and is called blind spot.

Muscles of the eye

oculomotor muscles- three pairs of striated skeletal muscles that are attached to the conjunctiva; carry out movement of the eyeball;

pupil muscles- smooth muscles of the iris (circular and radial), changing the diameter of the pupil;
The circular muscle (contractor) of the pupil is innervated by parasympathetic fibers from the oculomotor nerve, and the radial muscle (dilator) of the pupil is innervated by fibers of the sympathetic nerve. The iris thus regulates the amount of light entering the eye; in strong, bright light, the pupil narrows and limits the entry of rays, and in weak light, it expands, allowing more rays to penetrate. The diameter of the pupil is influenced by the hormone adrenaline. When a person is in excited state(during fear, anger, etc.), the amount of adrenaline in the blood increases, and this causes the pupil to dilate.
The movements of the muscles of both pupils are controlled from one center and occur synchronously. Therefore, both pupils always dilate or contract equally. Even if you apply bright light to only one eye, the pupil of the other eye also narrows.

lens muscles(ciliary muscles) - smooth muscles that change the curvature of the lens ( accommodation--focusing the image on the retina).

Wiring department

The optic nerve conducts light stimuli from the eye to the visual center and contains sensory fibers.

Moving away from the posterior pole of the eyeball, the optic nerve leaves the orbit and, entering the cranial cavity, through the optic canal, together with the same nerve on the other side, forms a chiasm ( chiasmus). After the chiasm, the optic nerves continue in visual tracts. The optic nerve is connected to the nuclei of the diencephalon, and through them to the cerebral cortex.

Each optic nerve contains the totality of all its processes nerve cells retina of one eye. In the area of ​​the chiasm, an incomplete crossover of fibers occurs, and each optic tract contains about 50% of the fibers of the opposite side and the same number of fibers of the same side.

Central department

The central section of the visual analyzer is located in occipital lobe cerebral cortex.

Impulses from light stimuli travel along the optic nerve to the cerebral cortex of the occipital lobe, where the visual center is located.

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Ministry of Education and Science Federal State Educational Institution of Higher Professional Education "ChSPU named after I.Ya. Yakovlev"

Department of Developmental, Pedagogical and Special Psychology

Test

in the discipline "Anatomy, physiology and pathology of the organs of hearing, speech and vision"

on the topic of:" Structure of the visual analyzer"

Completed by a 1st year student

Marzoeva Anna Sergeevna

Checked by: Doctor of Biological Sciences, Associate Professor

Vasilyeva Nadezhda Nikolaevna

Cheboksary 2016

• 1. The concept of the visual analyzer
• 2. Peripheral section of the visual analyzer
• 2.1 Eyeball
• 2.2 Retina, structure, functions
• 2.3 Photoreceptor apparatus
• 2.4 Histological structure of the retina
• 3. Structure and functions of the conductive section of the visual analyzer
• 4. Central department of the visual analyzer
• 4.1 Subcortical and cortical visual centers
• 4.2 Primary, secondary and tertiary cortical fields
• Conclusion
• List of used literature

1. The concept of visualom ananalyzer

The visual analyzer is a sensory system, including a peripheral section with a receptor apparatus (eyeball), a conducting section (afferent neurons, optic nerves and visual pathways), a cortical section, which represents a set of neurons located in the occipital lobe (17,18,19 lobe) cortex of the large hemispheres. With the help of a visual analyzer, the perception and analysis of visual stimuli is carried out, the formation of visual sensations, the totality of which gives a visual image of objects. Thanks to the visual analyzer, 90% of the information enters the brain.

2. Peripheral departmentvisual analyzer

Peripheral department of the visual analyzer - This is the organ of vision of the eyes. It consists of the eyeball and an auxiliary apparatus. The eyeball is located in the orbit of the skull. The accessory apparatus of the eye includes protective devices(eyebrows, eyelashes, eyelids), lacrimal apparatus, motor apparatus (eye muscles).

Eyelids - these are semilunar plates of fibrous connective tissue, they are covered on the outside with skin, and on the inside with mucous membrane (conjunctiva). The conjunctiva covers the anterior surface of the eyeball, except for the cornea. The conjunctiva limits the conjunctival sac, which contains tear fluid that washes the free surface of the eye. The lacrimal apparatus consists of the lacrimal gland and lacrimal ducts.

Lacrimal gland located in the upper-outer part of the orbit. Its excretory ducts (10-12) open into the conjunctival sac. Tear fluid protects the cornea from drying out and washes away dust particles. It flows through the lacrimal canaliculi into the lacrimal sac, which is connected by the nasolacrimal duct to the nasal cavity. The motor apparatus of the eye is formed by six muscles. They are attached to the eyeball, starting from the tendon end located around the optic nerve. The rectus muscles of the eye: lateral, medial superior and inferior - rotate the eyeball around the frontal and sagittal axes, turning it inward and outward, up and down. The superior oblique muscle of the eye, turning the eyeball, turns the pupil down and outward, the inferior oblique muscle of the eye - upward and outward.

2.1 Eyeball

The eyeball consists of membranes and a nucleus . Shells: fibrous (outer), vascular (middle), retina (inner).

Fibrous casing in front it forms a transparent cornea, which passes into the tunica albuginea or sclera. Cornea- a transparent membrane covering the front of the eye. It lacks blood vessels and has great refractive power. Part of the optical system of the eye. The cornea borders the opaque outer layer of the eye - the sclera. Sclera- the opaque outer layer of the eyeball, which passes into the transparent cornea in the front part of the eyeball. 6 extraocular muscles are attached to the sclera. It contains a small number of nerve endings and blood vessels. This outer shell protects the core and maintains the shape of the eyeball.

Choroid It lines the albuginea from the inside and consists of three parts that are different in structure and function: the choroid itself, the ciliary body located at the level of the cornea and iris (Atlas, p. 100). Adjacent to it is the retina, with which it is closely connected. The choroid is responsible for the blood supply to intraocular structures. In diseases of the retina, it is very often involved in the pathological process. There are no nerve endings in the choroid, so when it is diseased, there is no pain, which usually signals some kind of problem. The choroid proper is thin, rich in blood vessels, and contains pigment cells that give it dark brown color. visual analyzer perception brain

Ciliary body , which looks like a roller, protrudes into the eyeball where the tunica albuginea passes into the cornea. The posterior edge of the body passes into the choroid proper, and up to 70 ciliary processes extend from the anterior one, from which thin fibers originate, the other end of which is attached to the lens capsule along the equator. At the base of the ciliary body, in addition to the vessels, there are smooth muscle fibers that make up ciliary muscle.

Iris or iris - a thin plate, it is attached to the ciliary body, shaped like a circle with a hole inside (the pupil). The iris consists of muscles that, when contracted and relaxed, change the size of the pupil. It enters the choroid of the eye. The iris is responsible for the color of the eyes (if it is blue, it means there are few pigment cells in it, if it is brown, it means a lot). Performs the same function as the aperture in a camera, regulating the light flow.

Pupil - hole in the iris. Its size usually depends on the light level. The more light, the smaller the pupil.

Optic nerve - using the optic nerve, signals from nerve endings are transmitted to the brain

Nucleus of the eyeball - these are light-refracting media that form the optical system of the eye: 1) aqueous humor of the anterior chamber(it is located between the cornea and the anterior surface of the iris); 2) aqueous humor of the posterior chamber of the eye(it is located between the back surface of the iris and the lens); 3) lens; 4)vitreous(Atlas, p. 100). Lens It consists of a colorless fibrous substance, has the shape of a biconvex lens, and is elastic. It is located inside a capsule attached to the ciliary body by filiform ligaments. When the ciliary muscles contract (when viewing close objects), the ligaments relax and the lens becomes convex. This increases its refractive power. When the ciliary muscles relax (when viewing distant objects), the ligaments become tense, the capsule compresses the lens and it flattens. At the same time, its refractive power decreases. This phenomenon is called accommodation. The lens, like the cornea, is part of the optical system of the eye. Vitreous body - 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. Part of the optical system of the eye.

2. 2 Retina of the eye, structure, functions

The retina lines the choroid from the inside (Atlas, p. 100); it forms the anterior (smaller) and posterior (larger) parts. The posterior part consists of two layers: pigment, fused with the choroid, and medulla. The medulla contains light-sensitive cells: cones (6 million) and rods (125 million) Largest quantity cones in the central fovea of ​​the macula, located lateral to the disc (the exit point of the optic nerve). With distance from the macula, the number of cones decreases and the number of rods increases. Cones and net glasses are photoreceptors of the visual analyzer. Cones provide color perception, rods provide light perception. They contact bipolar cells, which in turn contact ganglion cells. The axons of ganglion cells form the optic nerve (Atlas, p. 101). There are no photoreceptors in the disk of the eyeball, this is the blind spot of the retina.

Retina, or retina, retina- the innermost of the three membranes of the eyeball, adjacent to the choroid along its entire length up to the pupil, - the peripheral part of the visual analyzer, its thickness is 0.4 mm.

Retinal neurons are the sensory part of the visual system that perceives light and color signals from the outside world.

In newborns, the horizontal axis of the retina is one third longer than the vertical axis, and during postnatal development, by adulthood, the retina takes on an almost symmetrical shape. By the time of birth, the structure of the retina is mainly formed, with the exception of the foveal part. Its final formation is completed by the age of 5 years of the child’s life.

Structure of the retina. Functionally there are:

back large (2/3) - visual (optical) part of the retina (pars optica retinae). It is a thin, transparent, complex cellular structure that is attached to underlying tissues only at the dentate line and near the optic disc. The remaining surface of the retina is freely adjacent to the choroid and is held in place by the pressure of the vitreous body and the thin connections of the pigment epithelium, which is important in the development of retinal detachment.

· smaller (blind) - ciliary , covering the ciliary body (pars ciliares retinae) and the posterior surface of the iris (pars iridica retina) to the pupillary edge.

In the retina there are

· distal section- photoreceptors, horizontal cells, bipolars - all these neurons form connections in the outer synaptic layer.

· proximal part- the inner synaptic layer, consisting of axons of bipolar cells, amacrine and ganglion cells and their axons, forming the optic nerve. All neurons of this layer form complex synaptic switches in the internal synaptic plexiform layer, the number of sublayers in which reaches 10.

The distal and proximal sections are connected by interplexiform cells, but unlike the connection of bipolar cells, this connection occurs in the opposite direction (feedback type). These cells receive signals from elements of the proximal retina, in particular from amacrine cells, and transmit them to horizontal cells through chemical synapses.

Retinal neurons are divided into many subtypes, which is associated with differences in shape, synaptic connections, determined by the nature of dendritic branching in different zones of the internal synaptic layer, where they are localized. complex systems synapses.

Synaptic invaginating terminals (complex synapses), in which three neurons interact: the photoreceptor, the horizontal cell and the bipolar cell, are the output section of the photoreceptors.

The synapse consists of a complex of postsynaptic processes that penetrate into the terminal. On the photoreceptor side, in the center of this complex there is a synaptic ribbon bordered by synaptic vesicles containing glutamate.

The postsynaptic complex is represented by two large lateral processes, always belonging to horizontal cells, and one or more central processes, belonging to bipolar or horizontal cells. Thus, the same presynaptic apparatus carries out synaptic transmission to 2nd and 3rd order neurons (if we assume that the photoreceptor is the first neuron). The same synapse provides feedback from horizontal cells, which plays an important role in the spatial and color processing of photoreceptor signals.

The synaptic terminals of cones contain many such complexes, while rod terminals contain one or several. The neurophysiological features of the presynaptic apparatus are that the release of the transmitter from the presynaptic endings occurs all the time while the photoreceptor is depolarized in the dark (tonic), and is regulated by a gradual change in the potential on the presynaptic membrane.

The mechanism for the release of transmitters in the synaptic apparatus of photoreceptors is similar to that in other synapses: depolarization activates calcium channels, incoming calcium ions interact with the presynaptic apparatus (vesicles), which leads to the release of the transmitter into the synaptic cleft. The release of the transmitter from the photoreceptor (synaptic transmission) is suppressed by calcium channel blockers, cobalt and magnesium ions.

Each of the major types of neurons has many subtypes, forming the rod and cone tracts.

The surface of the retina is heterogeneous in its structure and functioning. IN clinical practice In particular, when documenting fundus pathology, four areas are taken into account:

1. central area

2. equatorial region

3. peripheral area

4. macular area

The origin of the optic nerve of the retina is the optic disc, which is located 3-4 mm medially (towards the nose) from the posterior pole of the eye and has a diameter of about 1.6 mm. There are no light-sensitive elements in the area of ​​the optic nerve head, so this place does not provide visual sensation and is called a blind spot.

Lateral (to the temporal side) from the posterior pole of the eye there is a spot (macula) - a section of the retina yellow color, having an oval shape (diameter 2-4 mm). In the center of the macula there is a central fovea, which is formed as a result of thinning of the retina (diameter 1-2 mm). In the middle of the central fovea there is a dimple - a depression with a diameter of 0.2-0.4 mm; it is the place of greatest visual acuity and contains only cones (about 2500 cells).

In contrast to the other membranes, it comes from the ectoderm (from the walls of the optic cup) and, according to its origin, consists of two parts: the outer (photosensitive) and the inner (not perceiving light). The retina is distinguished by a dentate line, which divides it into two sections: light-sensitive and non-light-sensitive. The photosensitive section is located posterior to the dentate line and carries light-sensitive elements (the visual part of the retina). The part that does not perceive light is located anterior to the dentate line (blind part).

Structure of the blind part:

1. The iris part of the retina covers the posterior surface of the iris, continues into the ciliary part and consists of a two-layer, highly pigmented epithelium.

2. The ciliated part of the retina consists of a two-layer cuboidal epithelium (ciliated epithelium) covering the posterior surface of the ciliary body.

The nervous part (the retina itself) has three nuclear layers:

· the outer - neuroepithelial layer consists of cones and rods (the cone apparatus provides color perception, the rod apparatus provides light perception), in which light quanta are transformed into nerve impulses;

· middle - ganglion layer of the retina consists of the bodies of bipolar and amacrine neurons (nerve cells), the processes of which transmit signals from bipolar cells to ganglion cells);

· the inner - ganglion layer of the optic nerve consists of multipolar cell bodies, non-myelinated axons, which form the optic nerve.

The retina is also divided into an outer pigment part (pars pigmentosa, stratum pigmentosum), and an inner photosensitive nerve part (pars nervosa).

2 .3 Photoreceptor apparatus

The retina is the light-sensitive part of the eye, consisting of photoreceptors, which contains:

1. cones, responsible for color vision and central vision; length 0.035 mm, diameter 6 microns.

2. sticks, responsible mainly for black-and-white vision, dark vision and peripheral vision; length 0.06 mm, diameter 2 microns.

The outer segment of the cone is shaped like a cone. Thus, in the peripheral parts of the retina, rods have a diameter of 2-5 µm, and cones - 5-8 µm; in the fovea the cones are thinner and have a diameter of only 1.5 µm.

The outer segment of the rods contains the visual pigment - rhodopsin, and the cones - iodopsin. The outer segment of the rods is a thin, rod-like cylinder, while the cones have a conical tip that is shorter and thicker than the rods.

The outer segment of the stick is a stack of disks surrounded by an outer membrane, superimposed on each other, resembling a stack of packaged coins. In the outer segment of the rod there is no contact between the edge of the disc and the cell membrane.

In cones, the outer membrane forms numerous invaginations and folds. Thus, the photoreceptor disk in the outer segment of the rod is completely separated from the plasma membrane, and in the outer segment of the cones the disks are not closed and the intradiscal space communicates with the extracellular environment. Cones have a round, larger, lighter-colored nucleus than rods. From the nuclear-containing part of the rods, central processes extend - axons, which form synaptic connections with the dendrites of rod bipolars and horizontal cells. Cone axons also synapse with horizontal cells and with dwarf and planar bipolars. The outer segment is connected to the inner segment by a connecting leg - cilia.

The inner segment contains many radially oriented and densely packed mitochondria (ellipsoid), which are energy suppliers for photochemical visual processes, many polyribosomes, the Golgi apparatus and a small number of elements of the granular and smooth endoplasmic reticulum.

The area of ​​the internal segment between the ellipsoid and the nucleus is called the myoid. The nuclear-cytoplasmic body of the cell, located proximal to the internal segment, passes into the synaptic process, into which the endings of bipolar and horizontal neurocytes grow.

In the outer segment of the photoreceptor, primary photophysical and enzymatic processes of transformation of light energy into physiological excitation occur.

The retina contains three types of cones. They differ in visual pigment, which perceives rays of different wavelengths. The different spectral sensitivity of cones can explain the mechanism of color perception. 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. When the rods and cones are excited, the signals are first transmitted through successive layers of neurons in the retina itself, then into the nerve fibers of the visual tract, and finally into the cerebral cortex.

2 .4 Histological structure of the retina

The highly organized cells of the retina form 10 retinal layers.

In the retina, there are 3 cellular levels, represented by photoreceptors and neurons of the 1st and 2nd order, connected to each other (in previous manuals, 3 neurons were distinguished: bipolar photoreceptors and ganglion cells). The plexiform layers of the retina consist of axons or axons and dendrites of the corresponding photoreceptors and 1st and 2nd order neurons, which include bipolar, ganglion, amacrine and horizontal cells called interneurons. (list from the choroid):

1. Pigment layer . Most outer layer The retina, adjacent to the inner surface of the choroid, produces visual purple. The membranes of the finger-like processes of the pigment epithelium are in constant and close contact with the photoreceptors.

2. Second layer formed by the outer segments of photoreceptors, rods and cones . Rods and cones are specialized, highly differentiated cells.

Rods and cones are long, cylindrical cells that have an outer and an inner segment and a complex presynaptic ending (rod spherule or cone stalk). All parts of the photoreceptor cell are united by the plasma membrane. The dendrites of bipolar and horizontal cells approach and invaginate the presynaptic end of the photoreceptor.

3. External border plate (membrane) - located in the outer or apical part of the neurosensory retina and is a strip of intercellular adhesion. It is not actually a membrane, since it consists of permeable viscous tightly adjacent intertwined apical portions of Müller cells and photoreceptors; it is not a barrier to macromolecules. The external limiting membrane is called Verhoef's fenestrated membrane because the inner and outer segments of the rods and cones pass through this fenestrated membrane into the subretinal space (the space between the layer of cones and rods and the retinal pigment epithelium), where they are surrounded by an interstitial substance rich in mucopolysaccharides.

4. Outer granular (nuclear) layer - formed by photoreceptor nuclei

5. Outer mesh (reticular) layer - processes of rods and cones, bipolar cells and horizontal cells with synapses. It is the zone between two pools of blood supply to the retina. This factor is decisive in the localization of edema, liquid and solid exudate in the outer plexiform layer.

6. Inner granular (nuclear) layer - form the nuclei of first-order neurons - bipolar cells, as well as the nuclei of amacrine (in the inner part of the layer), horizontal (in the outer part of the layer) and Müller cells (the nuclei of the latter lie at any level of this layer).

7. Inner mesh (reticular) layer - separates the inner nuclear layer from the layer of ganglion cells and consists of a tangle of complex branching and intertwining processes of neurons.

A line of synaptic connections including the cone stalk, rod end, and bipolar cell dendrites forms the middle limiting membrane, which separates the outer plexiform layer. It delimits the vascular inner part retina. Outside the middle limiting membrane, the retina is avascular and dependent on the choroidal circulation of oxygen and nutrients.

8. Layer of ganglion multipolar cells. Retinal ganglion cells (second order neurons) are located in the inner layers of the retina, the thickness of which noticeably decreases towards the periphery (around the fovea the layer of ganglion cells consists of 5 or more cells).

9. Optic nerve fiber layer . The layer consists of the axons of ganglion cells that form the optic nerve.

10. Internal border plate (membrane) the most inner layer retina adjacent to the vitreous body. Covers the surface of the retina from the inside. It is the main membrane formed by the base of the processes of neuroglial Müller cells.

3 . Structure and functions of the conductive section of the visual analyzer

The conductive section of the visual analyzer begins from the ganglion cells of the ninth layer of the retina. The axons of these cells form the so-called optic nerve, which should be considered not as a peripheral nerve, but as an optic tract. The optic nerve consists of four types of fibers: 1) optic, starting from the temporal half of the retina; 2) visual, coming from the nasal half of the retina; 3) papillomacular, emanating from the macula area; 4) light, going to the supraoptic nucleus of the hypothalamus. At the base of the skull, the optic nerves of the right and left sides intersect. In a person with binocular vision, approximately half of the nerve fibers of the optic tract are crossed.

After the chiasm, each optic tract contains nerve fibers coming from the inner (nasal) half of the retina of the opposite eye and from the outer (temporal) half of the retina of the same side.

The fibers of the optic tract go without interruption to the thalamic region, where in the external geniculate body they enter into a synaptic connection with the neurons of the visual thalamus. Some of the fibers of the optic tract end in the superior colliculi. The participation of the latter is necessary for the implementation of visual motor reflexes, for example, movements of the head and eyes in response to visual stimuli. The external geniculate bodies are an intermediate link that transmits nerve impulses to the cerebral cortex. From here, third-order visual neurons travel directly to the occipital lobe of the brain

4. Central department of the visual analyzer

The central section of the human visual analyzer is located in the posterior part of the occipital lobe. Here the area of ​​the central fovea of ​​the retina (central vision) is projected predominantly. Peripheral vision presented in the more anterior part of the optic lobe.

The central section of the visual analyzer can be divided into 2 parts:

1 - nucleus of the visual analyzer of the first signal system - in the area of ​​the calcarine sulcus, which mainly corresponds to field 17 of the cerebral cortex according to Brodmann);

2 - the core of the visual analyzer of the second signal system - in the region of the left angular gyrus.

Field 17 generally matures at 3 to 4 years of age. It is the organ of higher synthesis and analysis of light stimuli. If field 17 is damaged, physiological blindness may occur. TO central department The visual analyzer includes fields 18 and 19, where zones with full representation of the visual field are found. In addition, neurons that respond to visual stimulation are found along the lateral suprasylvian fissure, in the temporal, frontal and parietal cortices. When they are damaged, spatial orientation is disrupted.

There are a large number of disks in the outer segments of rods and cones. They are actually folds of the cell membrane, “packed” into a stack. Each rod or cone contains approximately 1000 disks.

Both rhodopsin and color pigments- conjugated proteins. They are included in the disc membranes as transmembrane proteins. The concentration of these photosensitive pigments in the discs is so high that they account for about 40% of the total mass of the outer segment.

Main functional segments of photoreceptors:

1. outer segment, here is a photosensitive substance

2. internal segment containing cytoplasm with cytoplasmic organelles. Mitochondria are of particular importance - they play an important role in providing photoreceptor function with energy.

4. synaptic body (the body is part of the rods and cones, which connects with subsequent nerve cells (horizontal and bipolar), representing the next links of the visual pathway).

4 .1 Subcortical and cortical visualthisscience

IN lateral geniculate bodies, which are subcortical visual centers, the bulk of the axons of the retinal ganglion cells end and the nerve impulses are switched to the next visual neurons, called subcortical or central. Each of the subcortical visual centers receives nerve impulses coming from the homolateral halves of the retinas of both eyes. In addition, information also comes to the lateral geniculate body from the visual cortex (feedback). It is also assumed that there are associative connections between the subcortical visual centers and the reticular formation of the brain stem, which contributes to the stimulation of attention and general activity (arousal).

Cortical visual center has a very complex multifaceted system of neural connections. It contains neurons that respond only to the beginning and end of lighting. In the visual center, not only information is processed along boundary lines, brightness and color gradations, but also the direction of movement of an object is assessed. In accordance with this, the number of cells in the cerebral cortex is 10,000 times greater than in the retina. There is a significant difference between the number of cellular elements of the external geniculate body and the visual center. One neuron of the lateral geniculate body is connected to 1000 neurons of the visual cortical center, and each of these neurons, in turn, forms synaptic contacts with 1000 neighboring neurons.

4 .2 Primary, secondary and tertiary cortical fields

The structural features and functional significance of individual areas of the cortex make it possible to distinguish individual cortical fields. There are three main groups of fields in the cortex: primary, secondary and tertiary fields. Primary fields are associated with sensory organs and organs of movement on the periphery, they mature earlier than others in ontogenesis, and have the largest cells. These are the so-called nuclear zones of analyzers, according to I.P. Pavlov (for example, the field of pain, temperature, tactile and muscle-articular sensitivity in the posterior central gyrus of the cortex, the visual field in the occipital region, the auditory field in the temporal region and the motor field in the anterior central gyrus of the cortex).

These fields carry out the analysis of individual irritations entering the cortex from the corresponding receptors. When the primary fields are destroyed, so-called cortical blindness, cortical deafness, etc. occur. secondary fields, or peripheral zones of analyzers, which are connected to individual organs only through primary fields. They serve to summarize and further process incoming information. Individual sensations are synthesized in them into complexes that determine the processes of perception.

When secondary fields are damaged, the ability to see objects and hear sounds is retained, but the person does not recognize them and does not remember their meaning.

Both humans and animals have primary and secondary fields. The furthest from direct connections with the periphery are the tertiary fields, or the overlap zones of the analyzers. Only humans have these fields. They occupy almost half of the cortex and have extensive connections with other parts of the cortex and with nonspecific brain systems. These fields are dominated by the smallest and most diverse cells.

The main cellular element here is stellate neurons.

Tertiary fields are located in the posterior half of the cortex - at the boundaries of the parietal, temporal and occipital regions and in the anterior half - in the anterior parts of the frontal regions. In these zones, the largest number of nerve fibers connecting the left and right hemisphere, therefore their role is especially great in organizing the coordinated work of both hemispheres. Tertiary fields mature in humans later than other cortical fields; they carry out the most complex functions of the cortex. Processes of higher analysis and synthesis take place here. In tertiary fields, based on the synthesis of all afferent stimuli and taking into account traces of previous stimuli, goals and objectives of behavior are developed. According to them, motor activity is programmed.

The development of tertiary fields in humans is associated with the function of speech. Thinking (inner speech) is possible only with the joint activity of analyzers, the integration of information from which occurs in tertiary fields. With congenital underdevelopment of the tertiary fields, a person is not able to master speech (pronounces only meaningless sounds) and even the simplest motor skills (cannot dress, use tools, etc.). Perceiving and evaluating all signals from the internal and external environment, the cerebral cortex carries out the highest regulation of all motor and emotional-vegetative reactions.

Conclusion

Thus, the visual analyzer is a complex and very important tool in human life. It is not without reason that the science of the eyes, called ophthalmology, has become an independent discipline both because of the importance of the functions of the organ of vision and because of the peculiarities of the methods of its examination.

Our eyes provide the perception of the size, shape and color of objects, their relative position and the distance between them. A person receives most information about the changing external world through the visual analyzer. In addition, eyes also adorn a person’s face; it is not without reason that they are called the “mirror of the soul.”

The visual analyzer is very important for a person, and the problem of preserving good vision very relevant for humans. Comprehensive technical progress, the general computerization of our lives is an additional and severe burden on our eyes. Therefore, it is so important to maintain visual hygiene, which, in essence, is not so difficult: do not read in conditions that are uncomfortable for the eyes, protect your eyes at work with protective glasses, work on the computer intermittently, do not play games that can lead to eye injuries and so on. Thanks to vision, we perceive the world as it is.

List of usedthliterature

1. Kuraev T.A. and others. Physiology of the central nervous system: Textbook. allowance. - Rostov n/a: Phoenix, 2000.

2. Fundamentals of sensory physiology / Ed. R. Schmidt. - M.: Mir, 1984.

3. Rakhmankulova G.M. Physiology of sensory systems. - Kazan, 1986.

4. Smith, K. Biology of sensory systems. - M.: Binom, 2005.

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Here is a typical patient with such a lesion.

He carefully examines the image of glasses offered to him. He is confused and doesn't know what the image means. He begins to wonder: “A circle... and another circle... and a stick... a crossbar... probably this is a bicycle?” He examines the image of a rooster with beautiful multi-colored tail feathers and, not perceiving the phase of the whole image, says: “It’s probably a fire - these are the flames...”.

In cases of massive lesions of the secondary parts of the occipital cortex, the phenomena of optical agnosia can take on a severe character.

In cases of limited lesions in this area, they appear in more erased forms and appear only when viewing complex pictures or in experiments where visual perception is carried out under complicated conditions (for example, under time pressure). Such patients may mistake a telephone with a rotating dial for a watch, or a brown sofa for a suitcase, etc. They cease to recognize contour or silhouette images and find it difficult if the images are presented to them in “noisy” conditions, for example, when contour figures are crossed out with broken lines ( Fig. 56) or when they are composed of individual elements and included in a complex optical field (Fig. 57). All these defects are especially clear visual perception appear when experiments with perception are carried out under time pressure - 0.25-0.50 s (using a tachistoscope).

Naturally, the patient with optical agnosia, it turns out to be unable not only to perceive entire visual structures, but also to depict them . If he is given the task of drawing an object, it is easy to discover that his image of this object has disintegrated and that he can depict (or rather, designate) only its individual parts, giving a graphical listing of the details where normal person draws an image.

Basic principles of the structure of the visual analyzer.

There are several general principles structures of all analyzer systems:

A) the principle of parallel multichannel information processing, according to which information about different signal parameters is simultaneously transmitted through various channels of the analyzer system;

b) the principle of information analysis using neuron detectors, aimed at highlighting both relatively elementary and complex, complex characteristics of the signal, which is provided by different receptive fields;

V) the principle of consistent complication of information processing from level to level, in accordance with which each of them carries out its own analyzing functions;

G) topical principle("point to point") representation of peripheral receptors in the primary field of the analyzing system;

d) the principle of a holistic integrative representation of a signal in the central nervous system in conjunction with other signals, which is achieved due to the existence of a general model (scheme) of signals of a given modality (similar to the “spherical model of color vision”). In Fig. 17 and 18, A B C, D (color insert) shows the brain organization of the main analytical systems: visual, auditory, olfactory and cutaneous-kinesthetic. Different levels of analyzer systems are presented - from receptors to the primary zones of the cerebral cortex.

Humans, like all primates, are “visual” mammals; he receives basic information about the outside world through visual channels. Therefore, the role of the visual analyzer for human mental functions cannot be overestimated.

The visual analyzer, like all analyzing systems, is organized according to a hierarchical principle. The main levels of the visual system of each hemisphere are: the retina (peripheral level); optic nerve (II pair); the area where the optic nerves intersect (chiasm); optic cord (where the visual pathway exits the chiasm); external or lateral geniculate body (NKT or LCT); the cushion of the optic thalamus, where some fibers of the optic pathway end; the path from the external geniculate body to the cortex (visual radiance) and the primary 17th field of the cerebral cortex (Fig. 19, A, B, W

rice. 20; color insert). The functioning of the visual system is ensured by the II, III, IV and VI pairs of cranial nerves.

The defeat of each of the listed levels, or links, of the visual system is characterized by special visual symptoms, special visual impairments.

First level of the visual system- the retina of the eye is a very complex organ, which is called “a piece of the brain brought out.”

The receptor structure of the retina contains two types of receptors:

· ¦ cones (device of daytime, photopic vision);

· rods (twilight, scotopic vision apparatus).

When light reaches the eye, the photopic response that occurs in these elements is converted into impulses that are transmitted through various levels of the visual system to the primary visual cortex (field 17). The number of cones and rods is unevenly distributed in different areas of the retina; There are significantly more cones in the central part of the retina (fovea) - the zone of maximum clear vision. This zone is slightly shifted away from the exit point of the optic nerve - an area called the blind spot (papilla n. optici).

Humans are one of the so-called frontal mammals, i.e. animals whose eyes are located in the frontal plane. As a result, the visual fields of both eyes (that is, that part of the visual environment that is perceived by each retina separately) overlap. This overlap of visual fields is a very important evolutionary acquisition that allowed humans to perform precise manual manipulations under visual control, as well as providing accuracy and depth of vision ( binocular vision). Thanks to binocular vision, it became possible to combine images of an object appearing in the retinas of both eyes, which dramatically improved the perception of image depth and its spatial features.

The overlap area of ​​the visual fields of both eyes is approximately 120°. The monocular vision zone is approximately 30° for each eye; We see this zone with only one eye, if we fix the central point of the visual field common to both eyes.

Visual information perceived by two eyes or only one eye (left or right) Visual information perceived by two eyes or only one eye (left or right) is projected onto different parts of the retina and, therefore, enters different parts of the visual system.

In general, the areas of the retina located towards the nose from the midline (nasal sections) are involved in the mechanisms of binocular vision, and the areas located in the temporal sections (temporal sections) are involved in monocular vision.

In addition, it is important to remember that the retina is also organized according to the superior-inferior principle: its upper and lower sections are represented on different levels visual system in different ways. Knowledge about these structural features of the retina makes it possible to diagnose its diseases (Fig. 21; color insert).

The second level of the visual system- optic nerves (II pair). They are very short and located behind the eyeballs in front cranial fossa, on the basal surface of the cerebral hemispheres. Different fibers of the optic nerves carry visual information from different parts of the retina. Fibers from the inner parts of the retinas pass in the inner part of the optic nerve, from the outer parts - in the outer part, from the upper parts - in the upper part, and from the lower parts - in the lower part.

The chiasm area constitutes the third link of the visual system. As is known, in humans, incomplete crossover of the visual pathways occurs in the chiasm zone. Fibers from the nasal halves of the retinas enter the opposite (contralateral) hemisphere, and fibers from the temporal halves enter the ipsilateral hemisphere. Due to incomplete decussation of the visual pathways, visual information from each eye enters both hemispheres. It is important to remember that the fibers coming from the upper parts of the retinas of both eyes form the upper half of the chiasm, and those coming from the lower parts - the lower; fibers from the fovea also undergo partial decussation and are located in the center of the chiasma.

Fourth level of the visual system- external or lateral geniculate body (NKT or LCT). This is part of the visual thalamus, the most important of the thalamic nuclei, and is a large formation consisting of nerve cells where the second neuron of the visual pathway is concentrated (the first neuron is located in the retina). Thus, visual information, without any processing, comes directly from the retina to the NKT. In humans, 80% of the visual pathways coming from the retina end in the NKT, the remaining 20% ​​go to other formations (pillow of the visual thalamus, anterior colliculus, brainstem), which indicates high level corticalization of visual functions. The NKT, like the retina, is characterized by a topical structure, i.e. various areas The retina corresponds to different groups of nerve cells in the NKT. Besides, in different areas The NKT represents the areas of the visual field that are perceived by one eye (monocular vision zones), and the areas that are perceived by both eyes (binocular vision zones), as well as the region of the region that is perceived by both eyes (binocular vision zones), as well as the central vision area.

As mentioned above, in addition to the NKT, there are other instances where visual information is received - this is the pillow of the visual thalamus, the anterior colliculus and the brainstem. When they are damaged, no visual dysfunction as such occurs, which indicates a different purpose. The anterior colliculus is known to regulate a number of motor reflexes (such as start reflexes), including those that are “triggered” by visual information. Apparently, similar functions are performed by the thalamus cushion, which is associated with a large number of instances, in particular with the area of ​​the basal ganglia. Brain stem structures are involved in the regulation of general nonspecific brain activation through collaterals coming from the visual pathways. Thus, visual information going to the brainstem is one of the sources that supports the activity of the nonspecific system (see Chapter 3).

Fifth level of the visual system- optic radiance (Graziole bundle) is a rather extended area of ​​the brain located deep in the parietal and occipital lobes. This is a wide fan of fibers occupying a large space, carrying visual information from different parts of the retina to different areas of the 17th field of the cortex.

Last resort- primary 17th field of the cerebral cortex, located mainly on medial surface brain in the form of a triangle, which is directed deep into the brain. This is a significant area of ​​the cerebral cortex compared to the primary cortical fields of other analyzers, which reflects the role of vision in human life. The most important anatomical feature of the 17th field is the good development of the IV layer of the cortex, where visual afferent impulses arrive; Layer IV is connected to layer V, from where local motor reflexes are “launched,” which characterizes the “primary neural complex of the cortex” (G. I. Polyakov, 1965). The 17th field is organized according to the topical principle, i.e. different areas of the retina are represented in its different sections. This field has two coordinates: superior-inferior and anterior-posterior. Top part The 17th field is associated with top part retina, i.e. with the lower fields of vision; the lower part of the 17th field receives impulses from the lower parts of the retina, i.e., from the upper visual fields. The posterior part of the 17th field represents binocular vision; the anterior part represents peripheral monocular vision.

The visual sensory system, together with the auditory system, plays a special role in cognitive activity person.

Through the visual analyzer, a person receives up to 90% of information about the world around him. The following functions are associated with the activity of the visual analyzer: photosensitivity, determination of the shape of objects, their size, the distance of objects from the eye, perception of movement, color vision and binocular vision.

Structure and functions of the organ of vision. The organ of vision consists of the eyeball (eye) and the auxiliary organs of the eye, which are located in the orbit. The eyeball has a spherical shape.

It consists of three shells and a core. The outer shell is fibrous, the middle one is vascular, the inner one is photosensitive, reticular (retina). The nucleus of the eyeball includes the lens, vitreous body and liquid medium - aqueous humor.

The fibrous membrane is thick, dense, and has two sections: anterior and posterior. Anterior section occupies 1/5 of the surface of the eyeball. It is formed by a transparent, anteriorly convex cornea. The cornea is devoid of blood vessels and has high light refractive properties. The posterior section of the fibrous membrane is the tunica albuginea, which resembles the color of the white of a boiled chicken egg.

The tunica albuginea is formed by a dense fibrous connective tissue. The choroid is located under the tunica albuginea and consists of three parts that are different in structure and function: the choroid itself, the ciliary body and the iris. The choroid itself occupies a large back eyes.

It is thin, rich in blood vessels, and contains pigment cells that give it a dark brown color.

The ciliary body is located anterior to the choroid itself and has the appearance of a roller. From leading edge From the ciliary body, outgrowths extend to the lens - ciliary processes and thin fibers (ciliary belt), which are attached to the lens capsule along its equator. Most of the ciliary body consists of the ciliary muscle. During its contraction, this muscle changes the tension of the fibers of the ciliary girdle and thereby regulates the curvature of the lens, changing its refractive power.

The iris, or iris, is located between the cornea at the front and the lens at the back. It looks like a frontally located disk with a hole (pupil) in the middle. With its outer edge, the iris passes into the ciliary body. The inner, free edge of the iris limits the opening of the pupil. The connective tissue base of the iris contains blood vessels, smooth muscle and pigment cells.

The color of the eyes depends on the amount and depth of pigment - brown, black (if there is a large amount of pigment), blue, greenish (if there is little pigment). Bunches of smooth muscle cells have a dual direction and form the muscle that dilates the pupil and the muscle that constricts the pupil. These muscles regulate the amount of light entering the eye.

The retina, or retina, is adjacent to the choroid from the inside. The retina has two parts: the posterior optic and the anterior ciliary and iris. In the posterior visual part there are light-sensitive cells - photoreceptors. The anterior part of the retina (blind) is adjacent to the ciliary body and iris. It does not contain light-sensitive cells. The visual part of the retina has a complex structure. It consists of two sheets: the inner one is photosensitive and the outer one is pigmented. The cells of the pigment layer are involved in the absorption of light entering the eye and passing through the photosensitive layer of the retina. The inner layer of the retina consists of three layers of nerve cells: the outer layer, adjacent to the pigment layer, is photoreceptor, the middle layer is associative, and the inner layer is ganglionic.

The photoreceptor layer of the retina consists of neurosensory rod and cone cells, the outer segments of which (dendrites) are shaped like rods or cones. The disc-like structures of rod-shaped and cone-shaped neurocytes (rods and cones) contain photopigment molecules: in rods - sensitive to black and white light, in cones - sensitive to red, green and blue light. The number of cones in the human retina reaches 6-7 million, and the number of rods is 20 times more. Rods perceive information about the shape and illumination of objects, and cones perceive information about color.

The central processes (axons) of neurosensory cells (rods and cones) transmit visual impulses to the biopolar cells of the second cellular layer of the retina, which have contact with the ganglion neurocytes of the third (ganglionic) layer of the retina.

The ganglion layer consists of large neurocytes, the axons of which form the optic nerve. At the back of the retina there are two areas - the blind spot and the macula. The blind spot is where the optic nerve exits the eyeball. Here the retina does not contain light-sensitive elements. The macula is located in the posterior pole of the eye. This is the most light-sensitive area of ​​the retina.

The middle of its recess is called the central fossa. The line connecting the middle of the anterior pole of the eye with the central fovea is called the optical axis of the eye.

For better vision of the eyes, with the help of the extraocular muscles, it is installed so that the object in question and the central fossa are on the same axis. As already noted, the nucleus of the eyeball includes the lens, vitreous humor and aqueous humor. The lens is a transparent biconvex lens with a diameter of about 9 mm. The lens is located behind the iris. Between the lens at the back and the iris at the front is the posterior chamber of the eye, which contains a clear liquid - aqueous humor. Behind the lens is the vitreous body. The lens substance is colorless, transparent, dense. The lens does not have vessels or nerves. The lens is covered with a transparent capsule, which is connected to the ciliary body with the help of the ciliary girdle. When the ciliary muscle contracts or relaxes, the tension of the girdle fibers weakens or increases, which leads to a change in the curvature of the lens and its refractive power. nervous physiological vision

The vitreous fills the entire cavity of the eyeball between the retina at the back and the lens at the front.

It consists of a transparent jelly-like substance and has no blood vessels. Aqueous humor is secreted by the blood vessels of the ciliary processes. It fills the posterior and anterior chambers of the eye, communicating through the hole in the iris - the pupil. Aqueous humor flows from the posterior chamber to the anterior chamber, and from the anterior chamber into the veins at the border of the cornea and tunica albuginea eyes.