The visual analyzer is its departments and functions. The visual analyzer, its structure and functions, the organ of vision. Why do they say that the eye looks, but the brain sees?

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- penetrated by 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. Inflammatory processes do not develop in it. 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 mesh membrane that lines the back 2/3 of the inner surface of the eyeball.

The retina is made up of supporting cells that form a mesh-like structure, hence its name. Only its back part perceives light rays. The retina, in its development and function, is part of the 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 an excited state (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 the processes of the nerve cells of the 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 the occipital lobe of the 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.

Textbook for 8th grade

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 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.

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.

Light enters the eyeball through the pupil. The lens and vitreous body 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.

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.

Test your knowledge

What is an analyzer?
How does the analyzer work?
How does the eyeball work?
What is a blind spot?

Think

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 structure of the human visual analyzer

Understanding the analyzer

Represented by the perceptive department - receptors of the retina, optic nerves, conduction system and corresponding areas of the cortex in the occipital lobes of the brain.

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

All these organs make up our visual analyzer or visual system.

Having two eyes allows us to make our vision stereoscopic (that is, form a three-dimensional image). The right side of the retina in each eye transmits the “right side” of the image through the optic nerve to the right side of the brain, and the left side of the retina acts similarly.

Then the brain connects two parts of the image - right and left - together.

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

Structure of the eye

The eye can be called a complex optical device.

Its main task is to “transmit” the correct image to the optic nerve.

Main functions of the eye:

optical system that projects the image;

· a system that perceives and “encodes” the received information for the brain;

· “servicing” life support system.

The cornea is the transparent membrane that covers 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.

The anterior chamber of the eye is the space between the cornea and the iris.

It is filled with intraocular fluid.

The iris is shaped like a circle with a hole inside (the pupil). The iris consists of muscles 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, if it is brown, it means a lot). Performs the same function as the aperture in a camera, regulating the light flow.

The pupil is an opening in the iris. Its size usually depends on the level of illumination.

The more light, the smaller the pupil.

The lens is the “natural lens” of the eye. It is transparent, elastic - it can change its shape, almost instantly “focusing”, due to which a person sees well both near and far. Located in the capsule, held in place by the ciliary band.

The lens, like the cornea, is part of the optical system of the eye.

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

Part of the optical system of the eye.

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

photochemical reaction.

Rods are highly photosensitivity and allow you to see in low light; they are also responsible for peripheral vision. Cones, on the contrary, require more light for their work, but they allow you to see small details (responsible for central vision) and make it possible to distinguish colors. The largest concentration of cones is located in the central fossa (macula), which is responsible for the highest visual acuity.

The retina is adjacent to the choroid, but in many areas it is loose. This is where it tends to peel off in various retinal diseases.

The sclera is the opaque outer layer of the eyeball that merges at the front of the eyeball into the transparent cornea. 6 extraocular muscles are attached to the sclera. It contains a small number of nerve endings and blood vessels.

The choroid - lines the posterior part of the sclera, 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.

Optic Nerve - The optic nerve transmits signals from nerve endings to the brain.

Human biology

Textbook for 8th grade

Visual analyzer. Structure and functions of the eye

The eyes, the organ of vision, can be compared to a window into the world around us. 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 the motor and labor activity of a 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 an 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 the inside, a layer of pigment cells that absorb light is adjacent to the choroid, 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.

The lens and vitreous body 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.

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.

These visual defects can also be caused by congenital changes in the eyeball.

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

Test your knowledge

What is an analyzer?
How does the analyzer work?
Name the functions of the auxiliary apparatus of the eye.
How does the eyeball work?
What functions do the pupil and lens perform?
Where are the rods and cones located, what are their functions?
How does the visual analyzer work?
What is a blind spot?
How do myopia and farsightedness occur?
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.

Visual analyzer- this is a complex system of organs, which consists of a receptor apparatus represented by the organ of vision - the eye, conductive pathways and the final section - the perceptive areas of the cerebral cortex. The receptor apparatus includes, first of all, eyeball, which is formed by various anatomical formations. So, it consists of several shells. The outer shell is called sclera, or tunica albuginea. Thanks to it, the eyeball has a certain shape and is resistant to deformation. At the front of the eyeball is cornea, which, unlike the sclera, is completely transparent.

The choroid of the eye is located under the tunica albuginea. In its anterior part, deeper than the cornea, there is iris. In the center of the iris there is a hole - the pupil. The concentration of pigment in the iris is the determining factor for such a physical indicator as eye color. In addition to these structures, the eyeball contains lens, performing the functions of a lens. The main receptor apparatus of the eye is formed by the retina, which is the inner membrane of the eye.

The eye has its own assistive apparatus, which provides his movements and protection. The protective function is performed by structures such as eyebrows, eyelids, lacrimal sacs and ducts, and eyelashes. The function of conducting impulses from the eyes to the subcortical nuclei of the cerebral hemispheres brain perform visual nerves having a complex structure. Through them, information from the visual analyzer is transmitted to the brain, where it is processed with the further formation of impulses going to the executive organs.

The function of the visual analyzer is vision, then it would be the ability to perceive light, size, relative position and distance between objects with the help of the organs of vision, which is a pair of eyes.

Each eye is contained in a socket (socket) of the skull and has an accessory eye apparatus and an eyeball.

The accessory apparatus of the eye provides protection and movement of the eyes and includes: eyebrows, upper and lower eyelids with eyelashes, lacrimal glands and motor muscles. The back of the eyeball is surrounded by fatty tissue, which acts as a soft elastic cushion. Above the upper edge of the eye sockets there are eyebrows, the hair of which protects the eyes from liquid (sweat, water) that can flow down the forehead.

The front of the eyeball is covered by the upper and lower eyelids, which protect the eye from the front and help moisturize it. Hair grows along the front edge of the eyelids, which forms eyelashes, the irritation of which causes the protective reflex of closing the eyelids (closing the eyes). The inner surface of the eyelids and the anterior part of the eyeball, with the exception of the cornea, are covered with conjunctiva (mucous membrane). In the upper lateral (outer) edge of each eye socket there is a lacrimal gland, which secretes a fluid that protects the eye from drying out and ensures the cleanliness of the sclera and the transparency of the cornea. The uniform distribution of tear fluid on the surface of the eye is facilitated by blinking of the eyelids. Each eyeball is moved by six muscles, of which four are called rectus muscles and two are called oblique muscles. The eye protection system also includes the corneal (touching the cornea or a speck entering the eye) and pupillary locking reflexes.

The eye or eyeball has a spherical shape with a diameter of up to 24 mm and a weight of up to 7-8 g.

Hearing analyzer- a set of somatic, receptor and nervous structures, the activity of which ensures the perception of sound vibrations by humans and animals. S. a. consists of the outer, middle and inner ear, auditory nerve, subcortical relay centers and cortical sections.

The ear is an amplifier and transducer of sound vibrations. Through the eardrum, which is an elastic membrane, and the system of transmitting bones - the hammer, incus and stirrup - the sound wave reaches the inner ear, causing oscillatory movements in the fluid filling it.

The structure of the hearing organ.

Like any other analyzer, the auditory one also consists of three parts: the auditory receptor, hearing ova nerve with its pathways and the auditory zone of the cerebral cortex, where the analysis and evaluation of sound stimulation occurs.

The organ of hearing is divided into the outer, middle and inner ear (Fig. 106).

The outer ear consists of the pinna and the external auditory canal. The skin-covered ears are made of cartilage. They capture sounds and direct them into the ear canal. It is covered with skin and consists of an outer cartilaginous part and an inner bone part. Deep in the ear canal are hair and skin glands that secrete a sticky yellow substance called earwax. It traps dust and destroys microorganisms. The inner end of the external auditory canal is covered by the eardrum, which converts airborne sound waves into mechanical vibrations.

The middle ear is a cavity filled with air. It contains three auditory ossicles. One of them, the malleus, rests on the eardrum, the second, the stapes, rests on the membrane of the oval window, which leads to the inner ear. The third bone, the anvil, is located between them. The result is a system of bone levers that increases the force of vibration of the eardrum by approximately 20 times.

The middle ear cavity communicates with the pharyngeal cavity using the auditory tube. When swallowing, the entrance to the auditory tube opens, and the air pressure in the middle ear becomes equal to atmospheric pressure. Thanks to this, the eardrum does not bend in the direction where the pressure is less.

The inner ear is separated from the middle ear by a bone plate with two openings - oval and round. They are also covered with membranes. The inner ear is a bony labyrinth consisting of a system of cavities and tubules located deep in the temporal bone. Inside this labyrinth, as if in a case, there is a membranous labyrinth. It has two different organs: the organ of hearing and organ balance -vestibular apparatus . All cavities of the labyrinth are filled with liquid.

The hearing organ is located in the cochlea. Its spirally twisted channel bends around the horizontal axis in 2.5-2.75 turns. It is divided by longitudinal partitions into upper, middle and lower parts. The hearing receptors are located in the spiral organ located in the middle part of the canal. The liquid filling it is isolated from the rest: vibrations are transmitted through thin membranes.

Longitudinal vibrations of air carrying sound cause mechanical vibrations of the eardrum. With the help of the auditory ossicles, it is transmitted to the membrane of the oval window, and through it to the fluid of the inner ear (Fig. 107). These vibrations cause irritation of the receptors of the spiral organ (Fig. 108), the resulting excitations enter the auditory zone of the cerebral cortex and here they are formed into auditory sensations. Each hemisphere receives information from both ears, making it possible to determine the source of sound and its direction. If the sounding object is on the left, then impulses from the left ear come to the brain earlier than from the right. This small difference in time allows not only to determine the direction, but also to perceive sound sources from different parts of space. This sound is called surround or stereophonic.

Date: 04/20/2016

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A little about the structure of the visual analyzer
Functions of the iris and cornea
What does the refraction of the image on the retina give?
Auxiliary apparatus of the eyeball
Eye muscles and eyelids

The visual analyzer is a paired organ of vision, represented by the eyeball, the muscular system of the eye and the auxiliary apparatus. With the help of the ability to see, a person can distinguish the color, shape, size of an object, its illumination and the distance at which it is located. So the human eye is able to distinguish the direction of movement of objects or their immobility. A person receives 90% of information through the ability to see. The organ of vision is the most important of all the senses. The visual analyzer includes the eyeball with muscles and an auxiliary apparatus.

A little about the structure of the visual analyzer

The eyeball is located in the orbit on a fat pad, which serves as a shock absorber. With some diseases, cachexia (emaciation), the fat pad becomes thinner, the eyes sink deeper into the eye socket and it feels like they are “sunken”. The eyeball has three membranes:

protein;
vascular;
mesh.

The characteristics of the visual analyzer are quite complex, so they need to be sorted out in order.

The tunica albuginea (sclera) is the outermost layer of the eyeball. The physiology of this shell is designed in such a way that it consists of dense connective tissue that does not transmit light rays. The muscles of the eye that provide eye movements and the conjunctiva are attached to the sclera. The front part of the sclera has a transparent structure and is called the cornea. A huge number of nerve endings are concentrated on the cornea, providing its high sensitivity, and there are no blood vessels in this area. It is round and somewhat convex in shape, which allows for proper refraction of light rays.

The choroid consists of a large number of blood vessels that provide trophism to the eyeball. The structure of the visual analyzer is designed in such a way that the choroid is interrupted at the place where the sclera passes into the cornea and forms a vertically located disk consisting of a plexus of blood vessels and pigment. This part of the shell is called the iris. The pigment contained in the iris is different for each person, and it provides the color of the eyes. With some diseases, the pigment may decrease or be completely absent (albinism), then the iris becomes red.

In the central part of the iris there is a hole, the diameter of which varies depending on the intensity of illumination. Rays of light penetrate the eyeball onto the retina only through the pupil. The iris has smooth muscles - circular and radial fibers. It is responsible for the diameter of the pupil. Circular fibers are responsible for the constriction of the pupil; they are innervated by the peripheral nervous system and the oculomotor nerve.

The radial muscles are part of the sympathetic nervous system. These muscles are controlled from a single brain center. Therefore, the dilation and contraction of the pupils occurs in a balanced manner, regardless of whether one eye is exposed to bright light or both.

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Functions of the iris and cornea

The iris is the diaphragm of the eye apparatus. It regulates the flow of light rays onto the retina. The pupil narrows when fewer light rays reach the retina after refraction.

This happens when the light intensity increases. When lighting decreases, the pupil dilates and more light enters the fundus of the eye.

The anatomy of the visual analyzer is designed in such a way that the diameter of the pupils depends not only on lighting; this indicator is also influenced by some hormones of the body. For example, when frightened, a large amount of adrenaline is released, which can also act on the contractility of the muscles responsible for the diameter of the pupil.

The iris and cornea are not connected: there is a space called the anterior chamber of the eyeball. The anterior chamber is filled with liquid, which performs a trophic function for the cornea and is involved in the refraction of light as light rays pass through.

The third retina is the specific perceptive apparatus of the eyeball. The retina is formed by branched nerve cells that emerge from the optic nerve.

The retina is located immediately behind the choroid and lines most of the eyeball. The structure of the retina is very complex. Only the back part of the retina, which is formed by special cells: cones and rods, is capable of perceiving objects.

The structure of the retina is very complex. Cones are responsible for perceiving the color of objects, rods are responsible for the intensity of light. Rods and cones are interspersed, but in some areas there is a cluster of only rods, and in some there is a cluster of only cones. Light hitting the retina causes a reaction within these specific cells.

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What does the refraction of the image on the retina give?

As a result of this reaction, a nerve impulse is generated, which is transmitted along the nerve endings to the optic nerve, and then to the occipital lobe of the cerebral cortex. It is interesting that the pathways of the visual analyzer have complete and incomplete crossovers with each other. Thus, information from the left eye enters the occipital lobe of the cerebral cortex on the right and vice versa.

An interesting fact is that the image of objects after refraction on the retina is transmitted upside down.

In this form, information enters the cerebral cortex, where it is then processed. Perceiving objects as they are is an acquired skill.

Newborn babies perceive the world upside down. As the brain grows and develops, these functions of the visual analyzer are developed and the child begins to perceive the outside world in its true form.

The refraction system is presented:

anterior chamber;
posterior chamber of the eye;
lens;
vitreous body.

The anterior chamber is located between the cornea and iris. It provides nutrition to the cornea. The posterior chamber is located between the iris and the lens. Both the anterior and posterior chambers are filled with fluid, which is able to circulate between the chambers. If this circulation is disrupted, a disease occurs that leads to vision impairment and can even lead to its loss.

The lens is a biconvex transparent lens. The function of the lens is to refract light rays. If the transparency of this lens changes due to certain diseases, a disease such as cataract occurs. Currently, the only treatment for cataracts is lens replacement. This operation is simple and quite well tolerated by patients.

The vitreous body fills the entire space of the eyeball, providing a constant shape of the eye and its trophism. The vitreous body is represented by a gelatinous transparent liquid. When passing through it, light rays are refracted.

The human visual analyzer, or simply put, the eyes, has a rather complex structure and simultaneously performs a lot of different functions. It allows a person not only to distinguish objects. A person sees an image in color, which many other inhabitants of the Earth are deprived of. In addition, a person can determine the distance to an object and the speed of a moving object. Rotating the eyes provides a person with a large viewing angle, which is necessary for safety.

The human eye has the shape of an almost regular sphere. He very complicated, has many small parts and at the same time, on the outside it is a rather durable organ. The eye is located in the opening of the skull, called the orbit, and lies there on a fatty layer, which, like a pillow, protects it from injury. The visual analyzer is a rather complex part of the body. Let's take a closer look at how the analyzer works.

Visual analyzer: structure and functions

Sclera

The white membrane of the eye, consisting of connective tissue, is called the sclera. This connective tissue is quite strong. It provides a constant shape to the eyeball, which is necessary to maintain the unchanged shape of the retina. The sclera contains all other parts of the visual analyzer. The sclera does not transmit light radiation. Muscles are attached to it on the outside. These muscles help the eyes move. The part of the sclera located in front of the eyeball is completely transparent. This part is the cornea.

Cornea

There are no blood vessels in this part of the sclera. It is entangled in a dense web of nerve endings. They provide the highest sensitivity of the cornea. The shape of the sclera is a slightly convex sphere. This shape ensures the refraction of light rays and their concentration.

Vascular body

Inside the sclera along its entire inner surface lies the vascular body. Blood vessels tightly intertwine the entire inner surface of the eyeball, transmitting the flow of nutrients and oxygen to all cells of the visual analyzer. At the location of the cornea, the vascular body is interrupted and forms a dense circle. This circle is formed by intertwining blood vessels and pigment. This part of the visual analyzer is called the iris.

Iris

The pigment is individual for each person. It is the pigment that is responsible for what color the eyes of a particular person will be. For some diseases pigmentation decreases or disappears altogether. Then the person's eyes are red. In the middle of the iris there is a transparent hole, clear of pigment. This hole can change its size. It depends on the light intensity. The camera aperture is built on this principle. This part of the eye is called the pupil.

Pupil

Smooth muscles in the form of intertwining fibers are connected to the pupil. These muscles cause the pupil to constrict or dilate. The change in pupil size is related to the intensity of the light flux. If the light is bright, the pupil narrows, and in dim light it dilates. This ensures that the light flux reaches the retina of the eye. approximately the same strength. The eyes act synchronously. They rotate simultaneously, and when light hits one pupil, both constrict. The pupil is completely transparent. Its transparency ensures that light reaches the retina of the eye and forms a clear, undistorted image.

The size of the pupil diameter depends not only on the intensity of the lighting. In stressful situations, danger, during sex - in any situation when adrenaline is released in the body - the pupil also dilates.

Retina

The retina covers the inner surface of the eyeball with a thin layer. It converts a stream of photons into an image. The retina consists of specific cells - rods and cones. These cells connect to countless nerve endings. Rods and cones The surface of the retina of the eye is distributed generally evenly. But there are places where only cones or only rods accumulate. These cells are responsible for transmitting images in color.

Due to exposure to photons of light, a nerve impulse is formed. Moreover, impulses from the left eye are transmitted to the right hemisphere, and impulses from the right eye are transmitted to the left. An image is formed in the brain due to incoming impulses.

Moreover, the picture turns out upside down and the brain then processes and corrects this picture, giving it the correct orientation in space. This property of the brain is acquired by a person during the process of growth. It is known that newborn children see the world upside down and only after some time, the picture of their perception of the world becomes upside down.

In order to obtain a geometrically correct, undistorted image, the human visual analyzer contains a whole light refraction system. It has a very complex structure:

Anterior chamber of the eye
Posterior chamber of the eye
Lens
Vitreous body

The anterior chamber is filled with fluid. It is located between the iris and the cornea. The liquid contained in it is rich in many nutrients.

Between the iris and the lens is the posterior chamber. It is also filled with liquid. Both cameras are connected to each other. The liquid in these chambers constantly circulates. If, as a result of a disease, fluid circulation stops, a person’s vision deteriorates and such a person may even go blind.

The lens is a biconvex lens. It focuses light rays. The lens has muscles attached to it that can change the shape of the lens, making it thinner or more convex. The clarity of the image a person receives depends on this. This principle of image correction is used in cameras and is called focusing.

Thanks to these properties of the lens, we see a clear image of an object and can also determine the distance to it. Sometimes clouding of the lens occurs. This disease is called cataract. Medicine has learned to replace lenses. Modern doctors consider this operation easy.

Inside the eyeball is the vitreous humor. It fills its entire space and consists of a dense substance that has jelly consistency. The vitreous body maintains the eye's constant shape and thus maintains the geometry of the retina in a permanent spherical form. This allows us to see undistorted images. The vitreous body is transparent. It transmits light rays without delay and participates in their refraction.

The visual analyzer is so important for human life that nature provides a whole set of different organs designed to ensure proper functioning and maintain the health of his eyes.

Auxiliary apparatus

Conjunctiva

The thinnest layer covering the inner surface of the eyelid and the outer surface of the eye is called the conjunctiva. This protective film lubricates the surface of the eyeball, helps clean it from dust and maintains the surface of the pupil in a clean and transparent state. The conjunctiva contains substances that prevent the growth and reproduction of pathogenic microflora.

Lacrimal apparatus

The lacrimal gland is located in the area of the outer corner of the eye. It produces a special salty liquid that pours out through the outer corner of the eye and washes the entire surface of the visual analyzer. From there, the fluid flows down the duct and enters the lower parts of the nose.

Muscles of the eye

The muscles hold the eyeball, firmly fixing it in the socket, and, if necessary, turn the eyes up, down and to the sides. A person does not need to turn his head to look at an object of interest, and a person's viewing angle is approximately 270 degrees. In addition, the eye muscles change the size and configuration of the lens, thereby providing a clear, sharp image of the object of interest, regardless of the distance to it. The muscles also control the eyelids.

Eyelids

Movable flaps that cover the eye if necessary. The eyelids are made of skin. The lower part of the eyelids is lined with conjunctiva. The muscles attached to the eyelids ensure their closing and opening - blinking. Control of the eyelid muscles can be instinctive or conscious. Blinking is an important function for maintaining eye health. When blinking, the open surface of the eye is lubricated with the secretion of the conjunctiva, which prevents the development of various types of bacteria on the surface. Blinking may occur when an object approaches the eye to prevent mechanical damage.

A person can control the blinking process. He can slightly delay the interval between blinks or even blink the eyelids of one eye - wink. At the border of the eyelids, hairs grow - eyelashes.

Eyelashes and eyebrows.

Eyelashes are hairs that grow along the edges of the eyelids. Eyelashes are designed to protect the surface of the eye from dust and tiny particles present in the air. During strong wind, dust, and smoke, a person closes his eyelids and looks through his lowered eyelashes. This happens on a subconscious level. In this case, a mechanism is activated to protect the surface of the eye from foreign bodies entering it.

The eye is in the socket. At the top of the orbit there is a brow ridge. This is a protruding part of the skull that protects the eye from damage from falls and impacts. On the surface of the brow ridge, coarse hair grows - eyebrows, which protect against specks getting into it.

Nature provides a whole range of preventive measures to preserve human vision. Such a complex structure of an individual organ indicates its vital importance for preserving human life. Therefore, for any initial visual impairment, the most correct decision would be to consult an ophthalmologist. Take care of your eyesight.