The structure and operation of the human visual analyzer. Visual analyzer

14.07.2019 -

REPORT ON THE TOPIC:

PHYSIOLOGY OF THE VISUAL ANALYZER.

STUDENTS: Putilina M., Adzhieva A.

Teacher: Bunina T.P.

The visual analyzer (or visual sensory system) is the most important of the sense organs of humans and most higher vertebrates. It provides more than 90% of the information going to the brain from all receptors. Thanks to the rapid evolutionary development of visual mechanisms, the brain of carnivorous animals and primates has undergone dramatic changes and achieved significant perfection. Visual perception is a multi-link process, starting with the projection of an image onto the retina and excitation of photoreceptors and ending with the adoption by the higher parts of the visual analyzer, localized in the cerebral cortex, of a decision about the presence of a particular visual image in the field of view.

Structures of the visual analyzer:

Eyeball.

Auxiliary apparatus.

Structure eyeball:

The nucleus of the eyeball is surrounded by three membranes: outer, middle and inner.

The outer - very dense fibrous membrane of the eyeball (tunica fibrosa bulbi), to which the external muscles of the eyeball are attached, performs protective function and, thanks to turgor, determines the shape of the eye. It consists of an anterior transparent part - the cornea, and a posterior opaque whitish part - the sclera.

The middle, or choroid, layer of the eyeball plays important role in metabolic processes, providing nutrition to the eye and removing metabolic products. It is rich in blood vessels and pigment (pigment-rich choroidal cells prevent light from penetrating the sclera, eliminating light scattering). It is formed by the iris, the ciliary body and the choroid itself. In the center of the iris there is a round hole - the pupil, through which light rays penetrate into the eyeball and reach the retina (the size of the pupil changes as a result of the interaction of smooth muscle fibers - the sphincter and dilator, contained in the iris and innervated by the parasympathetic and sympathetic nerves). The iris contains varying amounts of pigment, which determines its color - “eye color”.

The inner, or reticular, shell of the eyeball (tunica interna bulbi), the retina, is the receptor part of the visual analyzer, here the direct perception of light, biochemical transformations of visual pigments, changes in the electrical properties of neurons and the transmission of information to the central nervous system occur. The retina consists of 10 layers:

Pigmentary;

Photosensory;

External limiting membrane;

Outer granular layer;

Outer mesh layer;

Inner granular layer;

Inner mesh;

Ganglion cell layer;

Layer of optic nerve fibers;

Internal limiting membrane

The central fovea (macula macula). The area of the retina containing only cones (color-sensitive photoreceptors); in connection with this, he has twilight blindness (hemerolopia); This area is characterized by miniature receptive fields (one cone - one bipolar - one ganglion cell), and as a result, maximum visual acuity

From a functional point of view, the membranes of the eye and its derivatives are divided into three apparatuses: refractive (light refractive) and accommodative (adaptive), forming optical system eyes, and sensory (receptive) apparatus.

Light refractive apparatus

The light-refracting apparatus of the eye is a complex system of lenses that forms a reduced and inverted image of the outside world on the retina; it includes the cornea, chamber humor - fluids of the anterior and posterior chambers of the eye, the lens, as well as the vitreous body, behind which lies the retina, which perceives light.

Lens (lat. lens) - a transparent body located inside the eyeball opposite the pupil; Being a biological lens, the lens is an important part of the light-refracting apparatus of the eye.

The lens is a transparent biconvex round elastic formation, circularly fixed to the ciliary body. The posterior surface of the lens is adjacent to the vitreous body, in front of it are the iris and the anterior and posterior chambers.

The maximum thickness of the lens of an adult is approximately 3.6-5 mm (depending on the accommodation tension), its diameter is about 9-10 mm. The radius of curvature of the anterior surface of the lens at rest of accommodation is 10 mm, and the posterior surface is 6 mm; at maximum accommodation stress, the anterior and posterior radii are compared, decreasing to 5.33 mm.

The refractive index of the lens is heterogeneous in thickness and averages 1.386 or 1.406 (core), also depending on the state of accommodation.

At rest of accommodation, the refractive power of the lens averages 19.11 diopters, at maximum accommodation voltage - 33.06 diopters.

In newborns, the lens is almost spherical, has a soft consistency and a refractive power of up to 35.0 diopters. Its further growth occurs mainly due to an increase in diameter.

Accommodation apparatus

The accommodative apparatus of the eye ensures the focusing of the image on the retina, as well as the adaptation of the eye to the intensity of light. It includes the iris with a hole in the center - the pupil - and the ciliary body with the ciliary band of the lens.

Focusing of the image is ensured by changing the curvature of the lens, which is regulated by the ciliary muscle. As the curvature increases, the lens becomes more convex and refracts light more strongly, tuning itself to seeing nearby objects. When the muscle relaxes, the lens becomes flatter and the eye adapts to see distant objects. In other animals, in particular cephalopods, during accommodation it is precisely the change in the distance between the lens and the retina that prevails.

The pupil is a variable-sized hole in the iris. It acts as the eye's diaphragm, regulating the amount of light falling on the retina. In bright light, the circular muscles of the iris contract and the radial muscles relax, while the pupil narrows and the amount of light entering the retina decreases, this protects it from damage. In low light, on the contrary, the radial muscles contract and the pupil dilates, letting more light into the eye.

ligaments of Zinn (ciliary bands). The processes of the ciliary body are directed to the lens capsule. In a relaxed state, the smooth muscles of the ciliary body have a maximum stretching effect on the lens capsule, as a result of which it is maximally flattened and its refractive ability is minimal (this occurs when viewing objects located at a great distance from the eyes); under conditions of a contracted state of the smooth muscles of the ciliary body, the opposite picture occurs (when examining objects close to the eyes)

The anterior and posterior chambers of the eye, respectively, are filled with aqueous humor.

Receptor apparatus of the visual analyzer. Structure and functions of individual layers of the retina

The retina is the inner layer of the eye, which has a complex multilayer structure. There are two types of photoreceptors with different functional significance - rods and cones and several types of nerve cells with their numerous processes.

Under the influence of light rays, photochemical reactions occur in photoreceptors, consisting of changes in light-sensitive visual pigments. This causes excitation of the photoreceptors, and then synaptic excitation of the rod and cone-related nerve cells. The latter form the actual nervous apparatus of the eye, which transmits visual information to the centers of the brain and participates in its analysis and processing.

AUXILIARY DEVICE

The accessory apparatus of the eye includes the protective devices and muscles of the eye. Protective devices include the eyelids with eyelashes, the conjunctiva and the lacrimal apparatus.

The eyelids are paired skin-conjunctival folds that cover the eyeball in front. The anterior surface of the eyelid is covered with thin, easily folded skin, under which lies the muscle of the eyelid and which on the periphery passes into the skin of the forehead and face. The posterior surface of the eyelid is lined with the conjunctiva. The eyelids have anterior edges of the eyelids that bear eyelashes and posterior edges of the eyelids that merge into the conjunctiva.

Between the upper and lower eyelids there is an eyelid fissure with medial and lateral angles. At the medial corner of the eyelid fissure, the anterior edge of each eyelid has a small elevation - the lacrimal papilla, at the top of which the lacrimal canaliculus opens with a pinhole. The thickness of the eyelids contains cartilage, which is closely fused with the conjunctiva and largely determines the shape of the eyelids. These cartilages are strengthened to the edge of the orbit by the medial and lateral ligaments of the eyelids. Quite numerous (up to 40) cartilage glands lie in the thickness of the cartilage, the ducts of which open near the free posterior edges of both eyelids. People working in dusty workshops often experience blockage of these glands with subsequent inflammation.

The muscular apparatus of each eye consists of three pairs of antagonistically acting oculomotor muscles:

Upper and lower straight lines,

Internal and external straight lines,

Upper and lower obliques.

All muscles, with the exception of the inferior oblique, begin as the levator muscles upper eyelid, from the tendon ring located around the optic canal of the orbit. Then the four rectus muscles are directed, gradually diverging, anteriorly and, after perforating Tenon’s capsule, their tendons fly into the sclera. The lines of their attachment are at different distances from the limbus: internal straight - 5.5-5.75 mm, lower - 6-6.6 mm, external - 6.9-7 mm, upper - 7.7-8 mm.

The superior oblique muscle from the optic foramen is directed to the bone-tendon block located at the upper inner corner of the orbit and, having spread across it, goes posteriorly and outward in the form of a compact tendon; attaches to the sclera in the upper outer quadrant of the eyeball at a distance of 16 mm from the limbus.

The inferior oblique muscle begins from the inferior bony wall of the orbit somewhat lateral to the entry into the nasolacrimal canal, runs posteriorly and outward between the inferior wall of the orbit and the inferior rectus muscle; attaches to the sclera at a distance of 16 mm from the limbus (inferior outer quadrant of the eyeball).

The internal, superior and inferior rectus muscles, as well as the inferior oblique muscle, are innervated by branches of the oculomotor nerve, the external rectus - by the abducens nerve, and the superior oblique - by the trochlear nerve.

When one muscle or another contracts, the eye moves around an axis that is perpendicular to its plane. The latter runs along the muscle fibers and crosses the rotation point of the eye. This means that for most oculomotor muscles (with the exception of the external and internal rectus muscles), the axes of rotation have one or another angle of inclination relative to the original coordinate axes. As a result, when such muscles contract, the eyeball makes a complex movement. So, for example, the superior rectus muscle, with the eye in the middle position, lifts it upward, rotates inwards and turns it slightly towards the nose. Vertical movements of the eye will increase as the angle of divergence between the sagittal and muscular planes decreases, i.e., when the eye turns outward.

All movements of the eyeballs are divided into combined (associated, conjugated) and convergent (fixation of objects at different distances due to convergence). Combined movements are those that are directed in one direction: up, right, left, etc. These movements are performed by muscles - synergists. So, for example, when looking to the right, the external rectus muscle contracts in the right eye, and the internal rectus muscle contracts in the left eye. Convergent movements are realized through the action of the internal rectus muscles of each eye. A variety of them are fusion movements. Being very small, they carry out particularly precise fixation of the eyes, thereby creating conditions for the unhindered merging of two retinal images into one solid image in the cortical section of the analyzer.

Perception of light

We perceive light due to the fact that its rays pass through the optical system of the eye. There, the excitation is processed and transmitted to the central parts of the visual system. The retina is a complex layer of the eye containing several layers of cells that vary in shape and function.

The first (outer) layer is the pigment layer, consisting of densely located epithelial cells containing the black pigment fuscin. It absorbs light rays, contributing to a clearer image of objects. The second layer is the receptor layer, formed by light-sensitive cells - visual receptors - photoreceptors: cones and rods. They perceive light and convert its energy into nerve impulses.

Each photoreceptor consists of a light-sensitive outer segment containing visual pigment, and an inner segment containing the nucleus and mitochondria, which provide energy processes in the photoreceptor cell.

Electron microscopic studies have revealed that the outer segment of each rod consists of 400-800 thin plates, or disks, with a diameter of about 6 microns. Each disk is a double membrane consisting of monomolecular layers of lipids located between layers of protein molecules. Retinal, which is part of the visual pigment rhodopsin, is associated with protein molecules.

The outer and inner segments of the photoreceptor cell are separated by membranes through which a bundle of 16-18 thin fibrils passes. The internal segment passes into a process, with the help of which the photoreceptor cell transmits excitation through the synapse to the bipolar nerve cell in contact with it.

A person has about 6-7 million cones and 110-125 million rods in the eye. Rods and cones are distributed unevenly in the retina. The central fovea of the retina (fovea centralis) contains only cones (up to 140,000 cones per 1 mm2). Towards the periphery of the retina, the number of cones decreases and the number of rods increases. The periphery of the retina contains almost exclusively rods. Cones function in bright light conditions and perceive colors; rods are receptors that perceive light rays under twilight vision conditions.

Stimulation of various areas of the retina shows that various colors are perceived best when light stimuli are applied to the fovea, where cones are located almost exclusively. As you move away from the center of the retina, color perception becomes worse. The periphery of the retina, where only the rods are located, does not perceive color. The light sensitivity of the cone apparatus of the retina is many times less than that of the elements associated with the rods. Therefore, at dusk in low light conditions, central cone vision is sharply reduced and peripheral rod vision predominates. Since rods do not perceive colors, a person does not distinguish colors at dusk.

Blind spot. The entry point of the optic nerve into the eyeball, the optic nipple, does not contain photoreceptors and is therefore insensitive to light; This is the so-called blind spot. The existence of a blind spot can be verified through the Marriott experiment.

Marriott performed the experiment like this: he placed two nobles at a distance of 2 m opposite each other and asked them to look with one eye at a certain point on the side - then it seemed to each that his counterpart had no head.

Oddly enough, it was only in the 17th century that people learned that there was a “blind spot” on the retina of their eyes, which no one had thought about before.

Retinal neurons. Inward from the layer of photoreceptor cells in the retina there is a layer of bipolar neurons, which are adjacent to a layer of ganglion nerve cells from the inside.

The axons of ganglion cells form the fibers of the optic nerve. Thus, the excitation that occurs in the photoreceptor under the action of light enters the fibers of the optic nerve through nerve cells - bipolar and ganglion.

Perception of images of objects

A clear image of objects on the retina is provided by the complex unique optical system of the eye, consisting of the cornea, fluids of the anterior and posterior chambers, lens and vitreous body. Light rays pass through the listed media of the optical system of the eye and are refracted in them according to the laws of optics. The lens is of primary importance for the refraction of light in the eye.

For a clear perception of objects, it is necessary that their image is always focused in the center of the retina. Functionally, the eye is adapted for viewing distant objects. However, people can clearly distinguish objects located at different distances from the eye, thanks to the ability of the lens to change its curvature, and, accordingly, the refractive power of the eye. The ability of the eye to adapt to clearly seeing objects located at different distances is called accommodation. Violation of the accommodative ability of the lens leads to impaired visual acuity and the occurrence of myopia or farsightedness.

Parasympathetic preganglionic fibers originate from the Westphal-Edinger nucleus (visceral part of the nucleus of the III pair cranial nerve) and then go as part of the III pair of cranial nerves to the ciliary ganglion, which lies immediately behind the eye. Here, preganglionic fibers form synapses with postganglionic parasympathetic neurons, which, in turn, send fibers as part of the ciliary nerves to the eyeball.

These nerves excite: (1) the ciliary muscle, which regulates the focusing of the eye lenses; (2) the iris sphincter, which constricts the pupil.

The source of sympathetic innervation of the eye is the neurons of the lateral horns of the first thoracic segment spinal cord. The sympathetic fibers emerging from here enter the sympathetic chain and ascend to the superior cervical ganglion, where they synapse with ganglion neurons. Their postganglionic fibers run along the surface of the carotid artery and further along smaller arteries and reach the eye.

Here, sympathetic fibers innervate the radial fibers of the iris (which dilate the pupil), as well as some extraocular muscles of the eye (discussed below in relation to Horner's syndrome).

The accommodation mechanism, which focuses the optical system of the eye, is important for maintaining high visual acuity. Accommodation occurs as a result of contraction or relaxation of the ciliary muscle of the eye. Contraction of this muscle increases the refractive power of the lens, and relaxation reduces it.

Lens accommodation is regulated by a negative feedback mechanism that automatically adjusts the refractive power of the lens to achieve the highest degree of visual acuity. When the eyes, focused on some distant object, must suddenly focus on a near object, the lens usually accommodates in less than 1 second. Although the exact regulatory mechanism that causes this rapid and accurate focusing of the eye is not clear, some of its features are known.

First, when the distance to the fixation point suddenly changes, the refractive power of the lens changes in the direction corresponding to the achievement of a new state of focus within a fraction of a second. Secondly, various factors help change the strength of the lens in the desired direction.

1. Chromatic aberration. For example, red rays are focused slightly behind the blue rays because blue rays are more refracted by the lens than red rays. The eyes appear to be able to determine which of these two types of rays is better focused, and this "key" transmits information to the accommodating mechanism to increase or decrease the power of the lens.

2. Convergence. When the eyes fixate on a near object, the eyes converge. The neural convergence mechanisms simultaneously send a signal that increases the refractive power of the eye lens.

3. The clarity of focus in the depth of the fovea is different compared to the clarity of focus at the edges, since the central fovea lies somewhat deeper than the rest of the retina. It is believed that this difference also provides a signal in which direction the lens power should be changed.

4. The degree of accommodation of the lens fluctuates slightly all the time with a frequency of up to 2 times per second. In this case, the visual image becomes clearer when the lens power fluctuates in the correct direction, and becomes less clear when the lens power fluctuates in the wrong direction. This can provide a quick signal to select the correct direction of change in lens power to ensure appropriate focus. The areas of the cerebral cortex that regulate accommodation function in close parallel connection with the areas that control fixation eye movements.

In this case, the analysis of visual signals is carried out in the areas of the cortex corresponding to Brodmann's fields 18 and 19, and motor signals to the ciliary muscle are transmitted through the pretectal zone of the brain stem, then through the Westphal-Edinger nucleus and ultimately through the parasympathetic nerve fibers to the eyes.

Photochemical reactions in retinal receptors

The retinal rods of humans and many animals contain the pigment rhodopsin, or visual purple, the composition, properties and chemical transformations of which have been studied in detail in recent decades. The pigment iodopsin is found in cones. The cones also contain the pigments chlorolab and erythrolab; the first of them absorbs rays corresponding to the green, and the second - to the red part of the spectrum.

Rhodopsin is a high molecular weight compound (molecular weight 270,000) consisting of retinal, an aldehyde of vitamin A, and a beam of opsin. Under the action of a light quantum, a cycle of photophysical and photochemical transformations of this substance occurs: retinal is isomerized, its side chain is straightened, the connection of retinal with the protein is broken, and the enzymatic centers of the protein molecule are activated. A conformational change in pigment molecules activates Ca2+ ions, which reach sodium channels through diffusion, as a result of which the conductivity for Na+ decreases. As a result of a decrease in sodium conductance, an increase in electronegativity occurs inside the photoreceptor cell relative to the extracellular space.

After which the retinal is cleaved from the opsin. Under the influence of an enzyme called retinal reductase, the latter is converted into vitamin A.

When the eyes darken, visual purple is regenerated, i.e. resynthesis of rhodopsin. This process requires that the retina receive the cis isomer of vitamin A, from which retinal is formed. If vitamin A is absent in the body, the formation of rhodopsin is sharply disrupted, which leads to the development of night blindness.

Photochemical processes in the retina occur very economically, i.e. When exposed to even very bright light, only a small part of the rhodopsin present in the rods is broken down.

The structure of iodopsin is close to rhodopsin. Iodopsin is also a compound of retinal with the protein opsin, which is formed in cones and differs from opsin in rods.

The absorption of light by rhodopsin and iodopsin is different. Iodopsin absorbs yellow light most strongly at a wavelength of about 560 nm.

Color perception

The perception of color begins with the absorption of light by cones - the photoreceptors of the retina (fragment below). The cone always responds to the signal in the same way, but its activity is transmitted to two various types neurons called ON- and OFF-type bipolar cells, which, in turn, are connected to ON- and OFF-type ganglion cells, and their axons carry a signal to the brain - first to the lateral geniculate body, and from there further to the visual cortex

Multicolor is perceived due to the fact that cones react to a certain spectrum of light in isolation. There are three types of cones. Type 1 cones respond predominantly to red, type 2 to green, and type 3 to blue. These colors are called primary. When exposed to waves of different lengths, each type of cone is excited differently.

The longest wavelength corresponds to red, the shortest to violet;

The colors between red and violet are arranged in the well-known sequence red-orange-yellow-green-blue-blue-violet.

Our eye perceives wavelengths only in the range of 400-700 nm. Photons with wavelengths above 700 nm are classified as infrared radiation and are perceived in the form of heat. Photons with wavelengths below 400 nm are classified as ultraviolet radiation, they are because of their high energy can have a damaging effect on the skin and mucous membranes; After ultraviolet comes X-ray and gamma radiation.

As a result, each wavelength is perceived as a special color. For example, when we look at a rainbow, the primary colors (red, green, blue) seem to be the most noticeable to us.

By optical mixing of primary colors, other colors and shades can be obtained. If all three types of cones are excited simultaneously and equally, the sensation of white color occurs.

Color signals are transmitted along the slow fibers of ganglion cells

As a result of the mixing of signals that carry information about color and shape, a person can see something that would not be expected based on an analysis of the wavelength of light reflected from an object, as illusions clearly demonstrate.

Visual pathways:

The axons of ganglion cells give rise to the optic nerve. The right and left optic nerves merge at the base of the skull to form the chiasm, where the nerve fibers coming from the inner halves of both retinas cross and pass to the opposite side. Fibers coming from the outer halves of each retina join together with a decussated bundle of axons from the contralateral optic nerve to form the optic tract. The optic tract ends in the primary centers of the visual analyzer, which include the lateral geniculate body, the superior colliculus and the pretectal region of the brain stem.

The lateral geniculate bodies are the first structure of the central nervous system where excitation impulses switch on the path between the retina and the cerebral cortex. Neurons of the retina and lateral geniculate body analyze visual stimuli, assessing their color characteristics, spatial contrast and average illumination in different parts of the visual field. In the lateral geniculate bodies, binocular interaction begins from the retina of the right and left eyes.

Understanding the analyzer

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

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

Having two eyes allows us to make our vision stereoscopic (that is, form a three-dimensional image). The right side of the retina of each eye transmits through the optic nerve" right side" images in right side brain, acts similarly left-hand side retina. 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 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 in it, 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 a hole in the iris. Its size usually depends on the light level. 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. These cells, which produce the enzyme rhodopsin, convert light energy (photons) into electrical energy nerve 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 are the ones that allow you to see small details (responsible for central vision), 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 choroid, but in many areas it is loose. This is where it tends to flake off when various diseases retina.

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; the retina is adjacent to it, 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 - with the help of the optic nerve, signals from nerve endings are transmitted to the brain.

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

Department of Developmental, Pedagogical and Special Psychology

Test

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

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

Completed by a 1st year student

Marzoeva Anna Sergeevna

Checked by: Doctor of Biological Sciences, Associate Professor

Vasilyeva Nadezhda Nikolaevna

Cheboksary 2016

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

1. The concept of visualom ananalyzer

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

2. Peripheral departmentvisual analyzer

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

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

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

2.1 Eyeball

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

Fibrous casing in front it forms a transparent cornea, which passes into the tunica albuginea or sclera. Cornea- a transparent membrane covering the front of the eye. It has no blood vessels and has great refractive power. Part of the optical system of the eye. The cornea borders the opaque outer layer of the eye - the sclera. Sclera- the opaque outer layer of the eyeball, which passes into the transparent cornea in the front part of the eyeball. 6 extraocular muscles are attached to the sclera. It contains a small number of nerve endings and blood vessels. This outer shell protects the core and maintains the shape of the eyeball.

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

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

Iris or iris - a thin plate, it is attached to ciliary body, 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 in it, if it is brown, it means a lot). Performs the same function as the aperture in a camera, regulating the light flow.

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

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

Nucleus of the eyeball - these are light-refracting media that form the optical system of the eye: 1) aqueous humor of the anterior chamber(it is located between the cornea and the anterior surface of the iris); 2) aqueous humor rear camera eyes(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, and has elasticity. It is located inside a capsule attached to the ciliary body by filiform ligaments. When the ciliary muscles contract (when viewing close objects), the ligaments relax and the lens becomes convex. This increases its refractive power. When the ciliary muscles relax (when viewing distant objects), the ligaments become tense, the capsule compresses the lens and it flattens. At the same time, its refractive power decreases. This phenomenon is called accommodation. The lens, like the cornea, is part of the optical system of the eye. Vitreous body - a gel-like transparent substance located in the back of the eye. The vitreous body maintains the shape of the eyeball and is involved in intraocular metabolism. Part of the optical system of the eye.

2. 2 Retina of the eye, structure, functions

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

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

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

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

Structure of the retina. Functionally there are:

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

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

In the retina there are

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

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

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

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

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

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

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

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

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

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

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

1. central area

2. equatorial region

3. peripheral area

4. macular area

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

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

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

Structure of the blind part:

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

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

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

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

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

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

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

2 .3 Photoreceptor apparatus

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

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

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

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

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

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

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

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

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

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

The retina contains three types of cones. They differ in visual pigment, which perceives rays of different wavelengths. The different spectral sensitivity of cones can explain the mechanism of color perception. In these cells, which produce the enzyme rhodopsin, the energy of light (photons) is converted into electrical energy of the nervous tissue, i.e. photochemical reaction. When rods and cones are excited, signals are first conducted through successive layers of neurons in the retina itself, then into the nerve fibers visual pathways and ultimately into the cerebral cortex.

2 .4 Histological structure of the retina

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

4. Central department of the visual analyzer

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

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

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

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

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

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

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

Main functional segments of photoreceptors:

1. outer segment, where the photosensitive substance is located

2. internal segment containing cytoplasm with cytoplasmic organelles. Special meaning have mitochondria - they play an important role in providing photoreceptor function with energy.

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

4 .1 Subcortical and cortical visualthisscience

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

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

4 .2 Primary, secondary and tertiary cortical fields

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

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

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

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

The main cellular element here is stellate neurons.

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

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

Conclusion

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

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

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

List of usedthliterature

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

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

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

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

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Components of vision and their functions

Let's start by considering the structure of the visual analyzer, consisting of:

eyeball;
conducting pathways - through them the picture recorded by the eye is fed to the subcortical centers, and then to the cerebral cortex.

Therefore, in general, three sections of the visual analyzer are distinguished:

peripheral – eyes;
conduction – optic nerve;
central – visual and subcortical zones of the cerebral cortex.

The visual analyzer is also called the visual secretory system. The eye includes the orbit as well as the ancillary apparatus.

The central part is located mainly in the occipital part of the cerebral cortex. The accessory apparatus of the eye is a system of protection and movement. IN the latter case inner part The eyelid has a mucous membrane called the conjunctiva. The protective system includes the lower and upper eyelids with eyelashes.

The sweat from the head goes down, but does not get into the eyes due to the existence of the eyebrows. Tears contain lysozyme, which kills harmful microorganisms that enter the eyes. Blinking the eyelids helps to regularly moisten the apple, after which the tears descend closer to the nose, where they enter the lacrimal sac. Then they move into the nasal cavity.

The eyeball moves constantly, for which 2 oblique and 4 rectus muscles are provided. U healthy person both eyeballs move in the same direction.

The diameter of the organ is 24 mm, and its weight is about 6-8 g. The apple is located in the orbit formed by the bones of the skull. There are three membranes: retina, choroid and outer.

Outdoor

The outer shell contains the cornea and sclera. The first has no blood vessels, but has many nerve endings. Nutrition is provided by intercellular fluid. The cornea allows light to pass through and also has a protective function, preventing damage to the inside of the eye. It has nerve endings: when even a little dust gets on it, cutting pain appears.

The sclera is either white or bluish in color. The oculomotor muscles are attached to it.

Average

IN middle shell Three parts can be distinguished:

the choroid, located under the sclera, has many vessels and supplies blood to the retina;
the ciliary body is in contact with the lens;
iris - the pupil reacts to the intensity of light that hits the retina (dilates in low light, contracts in strong light).

Internal

The retina is a brain tissue that allows the function of vision to be realized. It looks like a thin membrane adjacent over the entire surface to the choroid.

The eye has two chambers filled with clear fluid:

front;
rear

As a result, we can identify the factors that ensure the performance of all functions of the visual analyzer:

sufficient amount of light;
focusing the image on the retina;
accommodation reflex.

Oculomotor muscles

They are part of the auxiliary system of the organ of vision and visual analyzer. As noted, there are two oblique and four rectus muscles.

lower;
top.

lower;
lateral;
top;
medial.

Transparent media inside the eyes

They are necessary to transmit light rays to the retina, as well as refract them in the cornea. Then the rays enter the anterior chamber. Then refraction is carried out by the lens - a lens that changes the power of refraction.

There are two main visual impairments:

farsightedness;
myopia.

The first disorder occurs when the convexity of the lens decreases; myopia is the opposite. There are no nerves or blood vessels in the lens: development inflammatory processes excluded.

Binocular vision

To get one picture formed by two eyes, the picture is focused at one point. Such lines of vision diverge when looking at distant objects, and converge when looking at close objects.

Thanks to binocular vision, you can determine the location of objects in space in relation to each other, evaluate their distance, etc.

Vision hygiene

We examined the structure of the visual analyzer, and also figured out in a certain way how the visual analyzer works. And finally, it’s worth finding out how to properly monitor the hygiene of your visual organs to ensure their efficient and uninterrupted operation.

it is necessary to protect the eyes from mechanical impact;
It is necessary to read books, magazines and other textual information in good lighting, keep the object of reading at the proper distance - about 35 cm;
it is desirable that the light falls from the left;
reading at a short distance contributes to the development of myopia, since the lens has to remain in a convex state for a long time;
exposure to excessively bright lighting, which can destroy light-receiving cells, should not be allowed;
You should not read in transport or lying down, since in this case the focal length constantly changes, the elasticity of the lens decreases, and the ciliary muscle weakens;
a lack of vitamin A can cause a decrease in visual acuity;
frequent walks on fresh air – good prevention many eye diseases.

Summarizing

Consequently, it can be noted that the visual analyzer is a complex, but very important tool for ensuring quality life person. It is not for nothing that the study of the organs of vision has grown into a separate discipline - ophthalmology.

In addition to a specific function, eyes also play an aesthetic role, decorating human face. Therefore, the visual analyzer is a very important element of the body, it is very important to maintain hygiene of the visual organs, periodically come for examination to a doctor and eat right, maintain healthy image life.

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

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

The main substance of the cornea consists of a transparent connective tissue stroma and corneal bodies. In front, the cornea is covered with multilayered epithelium. Cornea ( cornea) the anterior most convex transparent part of the eyeball, one of the light-refracting media of the eye.

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

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

Photoreceptors signs rods cones Length 0.06 mm 0.035 mm Diameter 0.002 mm 0.006 mm Number 125 – 130 million 6 – 7 million Image Black and white Colored Substance Rhodopsin (visual purple) iodopsin location Predominant in the periphery Predominant in the central part of the retina Macula – a collection of cones, the blind spot – the exit point of the optic nerve (no receptors)

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

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

Farsightedness (hyperopia) is a feature of the refraction of the eye, consisting in the fact that images of distant objects at rest of accommodation are focused behind the retina. At a young age, if farsightedness is not too high, using accommodation voltage, you can focus the image on the retina. One of the causes of farsightedness may be a reduced size of the eyeball on the anterior-posterior axis. Almost all babies are farsighted. But with age, in most people this defect disappears due to the growth of the eyeball. The cause of age-related (senile) farsightedness (presbyopia) is a decrease in the ability of the lens to change curvature. This process begins at about 25 years of age, but only by 4050 years of age leads to a decrease in visual acuity when reading at the usual distance from the eyes (2530 cm).