Eyes - the organ of vision - can be compared to a window in the world... Approximately 70% of all information we receive with the help of sight, for example, about the shape, size, color of objects, distance to them, etc. The visual analyzer controls the motor and labor activity human; thanks to sight, we can study the experience accumulated by mankind through books and computer screens.

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

Eyebrows and eyelashes protect the eyes from dust. In addition, the brows wick away sweat from the forehead. Everyone knows that a person constantly blinks (2-5 movements for centuries in 1 minute). But do they know why? It turns out that the surface of the eye at the moment of blinking is moistened with tear fluid, which protects it from drying out, at the same time being cleared of dust. The lacrimal fluid is produced by the lacrimal gland. It contains 99% water and 1% salt. Up to I g of lacrimal fluid is released per day, it collects in the inner corner of the eye, and then enters the lacrimal canals, which bring it into nasal cavity... If a person cries, the lacrimal fluid does not have time to leave through the tubules into the nasal cavity. Then tears flow through the lower eyelid and drip down the face.

The eyeball is located in the recess of the skull - the eye socket. It has a spherical shape and consists of inner core, covered with three membranes: outer - fibrous, middle - vascular and inner - reticular. The fibrous membrane is subdivided into the posterior opaque part - the tunica albuginea, or sclera, and the anterior transparent part - the cornea. The cornea is a convex-concave lens through which light enters the interior of 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 opening - 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 permeated by a dense network of blood vessels that feed the eyeball. From inside to choroid there is a layer of pigment cells that absorb light, therefore, 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 shell of the eye. In the retina, receptors are located: rods (receptors for twilight light, which distinguish light from dark) and cones (they are less sensitive to light, but distinguish colors). Most of the cones are located on the retina, opposite the pupil, in the macula. Near this spot is the exit site of the optic nerve, there are no receptors, therefore it is called a 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 on the retina. Six oculomotor muscles provide such a position of the eyeball so that the image of the object would fall exactly on the retina, on its macula.

In the receptors of the retina, light is converted into nerve impulses, which are transmitted along the optic nerve to the brain through the nuclei of the midbrain (upper tubercles of the quadruple) and diencephalon (optic nuclei of the thalamus) - to the visual area of ​​the cerebral cortex located in the occipital region. The perception of color, shape, illumination of an object, its details, which began in the retina, ends with an analysis in the visual cortex. All information is collected here, it is deciphered and generalized. As a result of this, an idea of ​​the subject is formed.

Visual impairment. People's vision changes with age, as the lens loses its elasticity, the ability to change its curvature. In this case, the image of closely spaced objects is blurred - hyperopia develops. Another visual defect is myopia, when people, on the contrary, poorly see distant objects; it develops after prolonged stress, improper lighting. Myopia often occurs in school-age children due to improper work regime, poor illumination of the workplace. With myopia, the image of the object is focused in front of the retina, and with hyperopia - behind the retina and therefore is perceived as blurry. Congenital changes in the eyeball can also be the cause of these visual defects.

Nearsightedness and hyperopia are corrected with specially selected glasses or lenses.

• The human visual analyzer has tremendous sensitivity. So, we can distinguish a hole illuminated from the inside in a wall with a diameter of only 0.003 mm. A trained person (and women do it much better) 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. What are the functions of the eye auxiliary apparatus?
4. How does the eyeball work?
5. What are the functions of the pupil and lens?
6. Where are rods and cones located, what are their functions?
7. How does a visual analyzer work?
8. What is a blind spot?
9. How do myopia and hyperopia arise?
10. What are the causes of visual impairment?

Think

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

The organ of vision is formed by the eyeball and the auxiliary apparatus. The eyeball can move thanks to six oculomotor muscles. The pupil is a small opening 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 section: retinal receptors;

conduction department: optic nerve;

central section: the occipital lobe of the cerebral cortex.

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

Eye structures

The eye consists of eyeball and auxiliary apparatus.

Assistive apparatus of the eye

brows- sweat protection;

eyelashes- dust protection;

eyelids- mechanical protection and moisture maintenance;

lacrimal glands- located at the top of the outer edge of the orbit. It produces tears that moisturize, rinse, and disinfect the eye. Excess tear fluid is removed into the nasal cavity through lacrimal canal located in the inner corner of the eye socket .

Eyeball

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

It is located on a fat pad in the anterior orbit.

The eye has three shells:

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

choroid with outer iris and ciliary body- riddled with blood vessels(eye nutrition) and contains a pigment that prevents light from scattering 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- the mucous membrane that connects the eyeball with the skin.

The tunica albuginea (sclera)- outer durable shell of the eye; the inner part of the sclera is impervious to the set rays. Function: eye protection and light isolation;

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

Lens- a biconvex lens located behind the cornea. Lens function: focusing light beams. The lens has no vessels and nerves. It does not develop inflammatory processes... It contains a lot of proteins, which can sometimes lose their transparency, which leads 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 the light flux entering the eye. The diameter of the pupil is involuntarily changed by the smooth muscles of the iris when the light changes.

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

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

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

Retina (retina)- the receptor apparatus of the eye.

Retinal structure

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

The retina consists of supporting cells that form mesh structure where its name comes from. Light rays are perceived only by its back. The retina, in its development and function, is a part nervous system... All other parts of the eyeball play an auxiliary role for the retina's perception of visual stimuli.

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

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

the first neurons have rod and cone dendrites; these neurons are the end cells of the optic nerve, they perceive visual stimuli and are light receptors.

the second, bipolar neurons;

the third - multipolar neurons ( ganglion cells); axons depart from them, which stretch along the bottom of the eye and form the optic nerve.

Light-sensitive elements of the retina:

sticks- perceive brightness;

cones- perceive color.

The cones are slowly excited and only with bright light. They are able to perceive color. There are three types of cones in the retina. The former perceive red, the latter - 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 intermixed, but in some places they are very densely located, in others they are rare or absent altogether. For each nerve fiber there are about 8 cones and about 130 rods.

In the area of macular there are no rods on the retina - only cones, here the eye has the greatest visual acuity and the best perception of color. Therefore, the eyeball is in continuous motion, so that the part of the object under consideration 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 process of vision (twilight vision), and the eye does not distinguish between colors, vision turns out to be achromatic (colorless).

Nerve fibers leave the rods and cones, which, when combined, form the optic nerve. The exit point from the retina of the optic nerve is called optic disc... There are no light-sensitive 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 attach to the conjunctiva; carry out the movement of the eyeball;

pupil muscles- smooth muscles of the iris (circular and radial), which change the diameter of the pupil;
The circular muscle (constrictor) of the pupil is innervated by parasympathetic fibers from the oculomotor nerve, and the radial muscle (dilator) of the pupil is innervated by the fibers of the sympathetic nerve. The iris thus regulates the amount of light entering the eye; in strong, bright light, the pupil narrows and restricts the flow of rays, and in weak light it expands, making it possible to penetrate more rays. The diameter of the pupil is affected by the hormone adrenaline. When a person is in excited state(with 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 narrow in the same way. Even if only one eye is exposed to bright light, 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).

Conductor department

The optic nerve is a conductor of 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 cross ( chiasm). After the intersection, the optic nerves continue into visual tracts... The optic nerve is connected with the nuclei of the diencephalon, and through them - with the cerebral cortex.

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

Central department

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

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

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Ministry of Education and Science FGOU VPO "I.Ya. Yakovlev ChGPU"

Department of Development, Pedagogical and Special Psychology

Test

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

on the topic:" The structure of the visual analyzer"

Completed by a 1st year student

Marzoeva Anna Sergeevna

Checked by: Doctor of Biological Sciences, Associate Professor

Vasilieva Nadezhda Nikolaevna

Cheboksary 2016

• 1. Concept of the visual analyzer
• 2. Peripheral section of the visual analyzer
• 2.1 Eyeball
• 2.2 Retina, structure, function
• 2.3 Photoreceptor apparatus
• 2.4 Histological structure of the retina
• 3. The structure and functions of the conduction 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 visualohm analizator

The visual analyzer is a sensory system that includes 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 share) bark of the pain-chic hemispheres. With the help of the visual analyzer, the perception and analysis of visual stimuli is carried out, the formation of visual sensations, the combination 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 section of the visual analyzer is the organ of vision of the eye. It consists of an eyeball and an auxiliary apparatus. The eyeball is located in the orbit of the skull. The auxiliary apparatus of the eye includes protective devices(eyebrows, eyelashes, eyelids), lacrimal apparatus, locomotor apparatus (eye muscles).

Eyelids - these are lunate plates of fibrous connective tissue, they are covered with skin on the outside, and on the inside with a mucous membrane (conjunctiva). The conjunctiva covers the anterior surface of the eyeball, except for the cornea. The conjunctiva is limited by the conjunctival sac, it contains the 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. The lacrimal fluid prevents the cornea from drying out and washes away dust particles. It flows through the lacrimal canals into the lacrimal sac, which connects the nasolacrimal duct with the nasal cavity. The motor apparatus of the eye is formed by six muscles. They are attached to the eyeball and start from the tendon end around the optic nerve. The rectus muscles of the eye: lateral, medial upper and lower - rotate the eyeball around the frontal and sagittal axes, turning it inward and outward, upward and downward. The superior oblique muscle of the eye, turning the eyeball, draws the pupil down and outward, the lower oblique muscle of the eye - up and out.

2.1 Eyeball

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

Fibrous sheath in front forms a transparent cornea, which passes into the tunica albuginea or sclera. Cornea- the transparent membrane covering the front of the eye. There are no blood vessels in it, it has a great refractive power. It is included in the optical system of the eye. The cornea is bordered by the opaque outer shell of the eye - the sclera. Sclera- the opaque outer shell of the eyeball, passing in the front part of the eyeball into the transparent cornea. 6 oculomotor muscles are attached to the sclera. It contains a small number of nerve endings and blood vessels. This outer shell protects the nucleus and maintains the shape of the eyeball.

Choroid lining the inside of the white, 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). The retina is adjacent to it, 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, with its disease, pain does not occur, usually signaling any malfunction. The choroid itself is thin, rich in blood vessels, contains pigment cells that give it dark brown... visual analyzer perception brain

Ciliary body , having the form of a roller, protrudes into the eyeball where the tunica albuginea passes into the cornea. The posterior edge of the body passes into the choroid itself, and from the anterior one extends to "70 ciliary processes, from which thin filaments originate, with the other end 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 attaches to the ciliary body, similar in shape to a circle with a hole inside (pupil). The iris is made up of muscles that, when contracted and relaxed, change the size of the pupil. It enters the choroid. 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 there are a lot of brown). Performs the same function as the aperture in a camera, adjusting the light flux.

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

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

The nucleus of the eyeball 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 front 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 consists of a colorless fibrous substance, has the shape of a biconvex lens, has elasticity. It is located inside the capsule, which is attached by filamentous ligaments to the ciliary body. When the ciliary muscles contract (when looking at close objects), the ligaments relax and the lens becomes convex. This increases its refractive power. When the ciliary muscles are relaxed (when examining distant objects), the ligaments are stretched, the capsule squeezes the lens and it flattens. In this case, its refractive power decreases. This phenomenon is called accommodation. The lens, like the cornea, is part of the optical system of the eye. Vitreous - a gel-like transparent substance located in the back of the eye. The vitreous body maintains the shape of the eyeball, participates in intraocular metabolism. It is included in the optical system of the eye.

2. 2 Retina, structure, functions

The retina lines the choroid from the inside (Atlas, p. 100); it forms the anterior (smaller) and posterior (large) parts. The back part consists of two layers: pigment, growing together with the choroid and cerebral. The medulla contains light-sensitive cells: cones (6 million) and rods (125 million) The largest number cones in the central fossa of the macula, located outside of 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. The cones and net l glasses are the photoreceptors of the visual analyzer. Cones provide color perception, rods - light perception. They come in contact with bipolar cells, which in turn come in contact with ganglion cells. The axons of the ganglion cells form the optic nerve (Atlas, p. 101). In the disc of the eyeball, photoreceptors are absent from this 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 assumes an almost symmetrical shape. By the time of birth, the structure of the retina is mostly formed, with the exception of the foveal part. Its final formation is completed by the age of 5 years of the child's life.

Retinal structure. Functionally distinguish:

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 the underlying tissues only at the dentate line and near the optic nerve head. The rest of the retinal surface adjoins the choroid freely and is held by the pressure of the vitreous body and the thin bonds 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.

The retina is isolated

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

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

The distal and proximal sections connect interlexiform cells, but unlike the connection of bipolar cells, this connection is carried out in the opposite direction (by the type of feedback). 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 the difference in shape, synaptic connections, determined by the nature of dendritic branching in different zones of the inner synaptic layer, where complex systems synapses.

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

The synapse consists of a complex of postsynaptic processes that penetrate into the terminal. On the side of the photoreceptor, 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 neurons of the 2nd and 3rd order (if we assume that the photoreceptor is the first neuron). In the same synapse, feedback from horizontal cells is carried out, which plays an important role in the spatial and color processing of photoreceptor signals.

The synaptic terminals of the cones contain many such complexes, while the rod terminals contain one or more. The neurophysiological features of the presynaptic apparatus are that the release of the mediator 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 of release of mediators 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 a mediator into the synaptic cleft. The release of a mediator 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 pathways.

The surface of the reticular membrane is heterogeneous in its structure and functioning. V clinical practice, in particular, in documenting the pathology of the fundus, four of its areas are taken into account:

1.central area

2.equatorial region

3.the peripheral region

4.macular area

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

Lateral (to the temporal side) of the posterior pole of the eye 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 fossa, which is formed as a result of thinning of the retina (diameter 1-2 mm). In the middle of the central fossa lies a dimple - a depression with a diameter of 0.2-0.4 mm, it is the place of the greatest visual acuity, contains only cones (about 2500 cells).

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

Blind part structure:

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 ciliary part of the retina consists of a two-layer cubic epithelium (ciliary epithelium) that covers the posterior surface of the ciliary body.

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

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

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

Internal - the ganglion layer of the optic nerve consists of bodies of multipolar cells, myelin-free axons, which form the optic nerve.

Also, the retina is subdivided into the outer pigment part (pars pigmentosa, stratum pigmentosum), and the 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 those responsible for color vision and central vision; length 0.035 mm, diameter 6 microns.

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

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

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

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

In the cones, the outer membrane forms numerous invaginations, folds. Thus, the photoreceptor disc in the outer segment of the rod is completely separated from the plasma membrane, while in the outer segment of the cones the discs are not closed and the intradiscal space communicates with the extracellular environment. The cones have a rounded, larger and lighter colored nucleus than rods. Central processes - axons - which form synaptic connections with dendrites of rod bipolar, horizontal cells, branch off from the nucleus-containing part of the rods. The cone axons also have synapses with horizontal cells and with dwarf and flat bipolar cells. The outer segment is connected to the inner segment by a connecting leg - the cilium.

The inner segment contains many radially oriented and densely packed mitochondria (ellipsoid) that provide energy 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 inner segment between the ellipsoid and the nucleus is called the myoid. The nuclear-cytoplasmic body of the cell, located proximal to the inner segment, passes into the synaptic process, into which the ends 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 take place.

The retina contains three types of cones. They differ in visual pigment that perceives rays with different wavelengths. The different spectral sensitivity of the 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 conducted through successive layers of neurons of the retina itself, then into the nerve fibers of the optic pathways, and finally into the cerebral cortex.

2 .4 Histological structure of the retina

Highly organized retinal cells form 10 retinal layers.

In the retina, 3 cellular levels are distinguished, 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 are composed of axons or axons and dendrites of the corresponding photoreceptors and neurons of the 1st and 2nd order, which include bipolar, ganglionic, and amacrine and horizontal cells called interneurons. (list from choroid):

1. Pigment layer ... Most outer layer the retina, adjacent to the inner surface of the choroid, produces visual purple. The membranes of the digital 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 in which an outer and inner segment and a complex presynaptic ending (rod spherula or cone stem) are distinguished. All parts of the photoreceptor cell are united by the plasma membrane. Dendrites of bipolar and horizontal cells approach and invade the presynaptic end of the photoreceptor.

3. Outer boundary plate (membrane) - located in the outer or apical part of the neurosensory retina and is a band of intercellular adhesions. It is not really a membrane at its core, since it consists of permeable, viscous tightly intertwining apical portions of Müllerian cells and photoreceptors; it is not a barrier to macromolecules. The outer boundary membrane is called the Verhofe fenestrated membrane, since the inner and outer segments of 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 nuclei of photoreceptors

5. Outer mesh (reticular) layer - processes of rods and cones, bipolar cells and horizontal cells with synapses. It is the area between the 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 Muller 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.

The line of synaptic connections, including the stem of the cone, the rod end, and the dendrites of bipolar cells, forms the middle border membrane that separates the outer plexiform layer. It delimits the vascular inner part retina. Outside the middle border membrane, the retina is devoid of blood vessels and is dependent on choroidal oxygen and nutrient circulation.

8. Layer of ganglionic multipolar cells. Retinal ganglion cells (second-order neurons) are located in the inner layers of the retina, the thickness of which decreases markedly 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 the ganglion cells that form the optic nerve.

10. Internal boundary plate (membrane) the most the inner layer retina adjacent to the vitreous humor. Covers the inner surface of the retina. It is the main membrane formed by the base of the processes of Müller's neuroglial cells.

3 . The structure and functions of the conduction section of the visual analyzer

The conduction section of the visual analyzer starts from the ganglion cells of the ninth layer of the retina. The axons of these cells form the so-called optic nerve, which should not be viewed as a peripheral nerve, but as the 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 area of ​​the macula; 4) light, going to the supraoptic nucleus of the hypothalamus. In the region of the base of the skull, the optic nerves of the right and left sides intersect. In a person with binocular vision, about half of the nerve fibers of the optic tract intersect.

After the intersection, 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 synaptic connection with the neurons of the optic tubercle. Part of the fibers of the optic tract ends in the upper tubercles of the quadruple. 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 optic 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 back of the occipital lobe. Here, the region of the central fovea of ​​the retina (central vision) is mainly projected. Peripheral vision presented in the more anterior part of the visual lobe.

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

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

2 - the nucleus of the visual analyzer of the second signal system - in the area of ​​the left angular gyrus.

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

The outer segments of rods and cones have a large number of discs. They are actually folds of the cell membrane, "packed" in a stack. Each stick or cone contains approximately 1000 discs.

Both rhodopsin and color pigments- conjugated proteins. They are incorporated into 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.

The main functional segments of photoreceptors:

1. outer segment, there is a light-sensitive substance

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

4. synaptic body (body is a part of 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 visualtsentra

V lateral geniculate bodies, which are subcortical visual centers, the bulk of the axons of the retinal ganglion cells ends and nerve impulses are switched to the next visual neurons, called subcortical, or central. Each of the subcortical visual centers receives nerve impulses from the homolateral halves of the retinas of both eyes. In addition, information also enters the lateral geniculate bodies 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 brainstem, which stimulates 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 illumination. In the visual center, not only information processing is performed on the boundary lines, brightness and color gradation, but also the assessment of the direction of the object's movements. 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 lateral 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

Features of the structure and functional significance of individual sections of the cortex make it possible to distinguish individual cortical fields. There are three main groups of fields in the bark: primary, secondary and tertiary fields. Primary fields connected with the sense organs and organs of movement on the periphery, they mature earlier than others in ontogenesis, they have the largest cells. These are the so-called nuclear zones of the analyzers, according to I.P. Pavlov (for example, the field of pain, temperature, tactile and musculo-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 analyze individual stimuli entering the cortex from the corresponding receptors. When the primary fields are destroyed, so-called cortical blindness, cortical deafness, etc. secondary fields, or the peripheral zones of the analyzers, which are connected with individual organs only through the primary fields. They serve to summarize and further process the incoming information. Separate sensations are synthesized in them into complexes that determine the processes of perception.

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

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

The main cellular element here are star-shaped neurons.

Tertiary fields are located in the posterior half of the cortex - at the borders 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 perform the most complex functions of the cortex. This is where the processes of higher analysis and synthesis take place. In the tertiary fields, on the basis of the synthesis of all afferent stimuli and taking into account the traces of previous stimuli, the goals and objectives of behavior are developed. According to them, the programming of motor activity takes place.

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 (utters 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 emerged as 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 information about the changing external world most of all through the visual analyzer. In addition, the eyes still adorn a person's face, it is not for nothing 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 to humans. Comprehensive technical progress, general computerization of our life - this is an additional and tough load on our eyes. Therefore, it is so important to observe hygiene of vision, which, in essence, is not so difficult: do not read in uncomfortable conditions for the eyes, protect eyes at work with protective glasses, work on the computer intermittently, do not play games that can lead to eye injuries etc. Through vision, we perceive the world as it is.

List usedthliterature

1. Kuraev T.A. and other 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 does not know what this image means. He begins to wonder: "A circle ... and another circle ... and a stick ... a crossbar ... perhaps 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: "Probably, this is 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 gross character.

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

Naturally, the patient with optic agnosia is 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 find that the image of this object has disintegrated and that he can depict (or rather, designate) only its individual parts, giving a graphical listing of 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, in accordance with which information about different signal parameters is simultaneously transmitted through different channels of the analyzer system;

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

v) the principle of sequential complication of information processing from level to level, in accordance with which each of them carries out its own analytic functions;

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

e) the principle of 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 common model (scheme) of signals of this modality (by the type of "spherical model of color vision"). In fig. 17 and 18, A B C, D (color insert) shows the cerebral organization of the main analytic systems: visual, auditory, olfactory and skin-kinesthetic. Various levels of analytic systems are presented - from receptors to the primary zones of the cerebral cortex.

Man, like all primates, belongs to "visual" mammals; he receives basic information about the outside world through visual channels. Therefore, the role of the visual analyzer for human mental functions can hardly 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: retina (peripheral level); optic nerve (II pair); the area of ​​intersection of the optic nerves (chiasm); the optic cord (the point of exit of the visual path from the chiasm area); external or lateral geniculate body (tubing or LCT); cushion of the optic hillock, where some fibers of the optic path end; path from the lateral geniculate body to the cortex (visual radiance) and the primary 17th field of the cerebral cortex (Fig. 19, A, B, C

rice. twenty; color insert). The work of the visual system is provided 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 impairment.

The 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 retinal receptor structure contains two types of receptors:

· ¦ cones (daytime, photopic vision apparatus);

· ¦ sticks (apparatus of twilight, scotopic vision).

When light reaches the eye, the photopic response arising 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 much more cones in the central part of the retina (fovea) - the zone is maximally clear vision... This zone is slightly shifted to the side of the exit site of the optic nerve - an area called the blind spot (papilla n. Optici).

Man is one of the so-called frontal mammals, that is, 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 hand manipulations under visual control, as well as ensure the accuracy and depth of vision ( binocular vision). Thanks to binocular vision, it became possible to combine the images of an object that appear in the retinas of both eyes, which sharply improved the perception of the depth of the image and its spatial features.

The overlapping area of ​​the visual fields of both eyes is approximately 120 °. The monocular vision area is about 30 ° for each eye; we see this zone with only one eye, if we fix the central point of the field of view 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, areas of the retina located nasally from the midline (nosal regions) are involved in binocular vision mechanisms, and areas located in the temporal regions (temporal regions) are involved in monocular vision.

In addition, it is important to remember that the retina is also organized according to the upper-lower principle: its upper and lower sections are represented on different levels the 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 the anterior cranial fossa, on the basal surface of the cerebral hemispheres. Different fibers of the optic nerves carry visual information from different parts of the retinas. Fibers from the inner sections of the retinas pass in the inner part of the optic nerve, from the outer sections - in the outer, from the upper sections - in the upper, and from the lower ones - in the lower.

The chiasm area is the third link of the visual system.... As you know, in a person in the chiasm zone, an incomplete intersection of the visual pathways occurs. Fibers from the nosal halves of the retinas enter the opposite (contralateral) hemisphere, and the fibers from the temporal halves enter the ipsilateral hemisphere. Due to the incomplete intersection 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; the fibers from the fovea also undergo partial crossover and are located in the center of the chiasm.

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

As mentioned above, in addition to the NKT, there are other instances where visual information enters - this is the cushion of the optic tubercle, the anterior colliculus and the brainstem. When they are damaged, no violations of visual functions as such arise, which indicates their other 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 cushion of the optic hillock, associated with a large number of instances, in particular, with the area of ​​the basal nuclei. Brain stem structures are involved in the regulation of general nonspecific activation of the brain through collaterals from the visual tract. Thus, visual information going to the brain stem is one of the sources that support the activity of the nonspecific system (see Chapter 3).

The fifth level of the visual system- visual radiance (Graziole's bundle) - a fairly extended area of ​​the brain, located in the depths of the parietal and occipital lobes. This is a wide fan of fibers that occupies a large space, carrying visual information from different parts of the retina to different areas of the 17th field of the cortex.

Last resort- the primary 17th field of the cerebral cortex, located mainly on medial surface the brain in the form of a triangle, which is directed with a point deep into the brain. This is a significant area of ​​the cerebral cortex in comparison with 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 a good development of the IV layer of the cortex, where visual afferent impulses come; Layer IV is associated with layer V, from where local motor reflexes are "triggered", which characterizes the "primary neural complex of the cortex" (GI Polyakov, 1965). The 17th field is organized according to the topical principle, that is, different areas of the retina are represented in its different areas. This field has two coordinates: top-bottom and front-back. Top part 17th field is associated with top retina, i.e. with lower visual fields; the lower part of the 17th field receives impulses from the lower parts of the retina, that is, from the upper fields of view. In the rear part of the 17th field, binocular vision is presented in the front part - peripheral monocular vision.

The visual sensory system, together with the auditory system, play a special role in cognitive activities 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, determining the shape of objects, their size, distance of objects from the eye, perception of movement, color vision and binocular vision.

The 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 is spherical.

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 a liquid medium - aqueous humor.

The fibrous membrane is thick, dense, it 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 part of the fibrous membrane - the white membrane, resembles in color the protein of a boiled chicken egg.

A dense fibrous membrane is formed connective tissue... The choroid is located under the albugine 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 part 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 form of a roller. From leading edge of the ciliary body, outgrowths branch off to the lens - ciliary processes and thin fibers (ciliary girdle), which attach to the lens capsule along its equator. Most of the ciliary body is made up 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 front cornea and the back of the lens. It looks like a front disc 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 defines the opening of the pupil. The connective tissue base of the iris contains vessels, smooth muscle and pigment cells.

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

The retina, or retina, is adjacent to the choroid from the inside. In the retina, two parts are distinguished: the posterior visual 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 the 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 light-sensitive 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 light-sensitive layer of the retina. The inner layer of the retina consists of three layers of nerve cells: the outer one, adjacent to the pigment layer, is photoreceptor, the middle is associative, and the inner is ganglion.

The photoreceptor layer of the retina consists of neurosensory rods and cone-shaped cells, the outer segments of which (dendrites) are rod-shaped or cone-shaped. 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 retina of the human eye reaches 6-7 million, and the number of rods is 20 times more. The rods perceive information about the shape and illumination of objects, while the cones perceive information about the color.

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

The ganglion layer consists of large neurocytes, the axons of which form the optic nerve. In the back of the retina, two areas are distinguished - a blind spot and a yellow spot. The blind spot is the exit point from the eyeball of the optic nerve. Here, the retina contains no light-sensitive elements. The macula is located in the region of the posterior pole of the eye. This is the most light-sensitive area of ​​the retina.

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

For better vision of the eyes with the help of the oculomotor 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 in front is the posterior chamber of the eye, which contains a transparent liquid - aqueous humor. Behind the lens is the vitreous humor. The substance of the lens is colorless, transparent, dense. The lens has no vessels and nerves. The lens is covered with a transparent capsule, which is connected to the ciliary body by means of a ciliary band. 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 body fills the entire cavity of the eyeball between the retina in the back and the lens in front.

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