The structure and functions of the visual analyzer. Body of sight

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

It can hardly be said that some sense organ is more significant than the rest. They complement each other, creating a complete picture of the world. But the fact that most of all information is up to 90%! - people perceive with the help of the eyes - this is a fact. To understand how this information gets to the brain and how its analysis takes place, one must imagine the structure and functions of the visual analyzer.

Features of the visual analyzer

Thanks to visual perception, we learn about the size, shape, colors, mutual arrangement of objects of the surrounding world, their movement or immobility. This is a complex and multi-stage process. The structure and functions of the visual analyzer - the system that provides the receiving and processing of visual information, and thereby providing vision - are very complex. Initially, it can distinguish peripheral (perceiving the initial data), conductive and analyzing parts. The information is obtained through the receptor apparatus, which includes the eyeball and auxiliary systems, and then it is sent by means of optic nerves to the corresponding centers of the brain, where its processing takes place and visual images are formed. All the departments of the visual analyzer will be considered in the article.

How the eye works. Outer layer of the eyeball

Eyes are a paired organ. Each eyeball in shape resembles a slightly flattened ball and consists of several shells: external, middle and inner, surrounding the fluid filled cavity of the eye.

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

The cornea is the refracting environment of the eye, it is convex, has the form of a lens and consists, in turn, of several layers. There are no blood vessels in it, but there are a lot of nerve endings. A white or bluish sclera, the visible part of which is usually called the eye protein, is formed from connective tissue. To her, and muscles are attached, providing eye turns.

Middle layer of the eyeball

The middle vascular membrane participates in metabolic processes, providing nutrition to the eye and the withdrawal of metabolic products. The front, the most conspicuous part of it is the iris. The pigmented substance in the iris, or more precisely, its amount, determines the individual shade of the human eye: from the blue, if it is small, to the brown, if enough. If the pigment is absent, as happens with albinism, then we can see the interlacing of the vessels, and the iris acquires a red color.

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

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

Retina

The inner, the thinnest layer, is the mesh shell, or the retina formed by nerve cells. Here there is a direct perception and a primary analysis of visual information. The back of the retina consists of special photoreceptors, called cones (their 7 million) and chopsticks (130 million). They are responsible for the perception of objects with the eye.

The cones are responsible for recognizing the color and provide central vision, allowing you to see the smallest details. Wands, being more sensitive, allow a person to see in black and white colors in conditions of poor lighting, and also responsible for peripheral vision. Most cones are concentrated in the so-called yellow spot opposite the pupil, somewhat above the entrance of the optic nerve. This place corresponds to the maximum visual acuity. The retina, as, indeed, all the departments of the visual analyzer, the structure has a difficult - in its structure, 10 layers are distinguished.

Structure of the cavity of the eye

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

Behind the lens, adjacent to it and further to the entire surface of the retina, is a vitreous body. It is a transparent gelatinous substance that fills most of the volume of the organ of vision. 98% of this gel-like substance is water. The purpose of this substance is carrying out light rays, compensating for intraocular pressure drops, maintaining the constancy of the shape of the eyeball.

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

Light refraction

The visual analyzer system is such that initially the light rays refract and focus on the cornea and pass through the anterior chamber to the iris. Through the pupil, the central part of the light stream hits the lens, where it focuses more precisely, and then through the vitreous body - onto the retina. The image of the object is projected on the retina in a reduced and inverted form, and the energy of the light rays is converted into nerve impulses by the photoreceptors. Information further through the optic nerve enters the brain. The place on the retina through which the optic nerve passes is devoid of photoreceptors, therefore it is called a blind spot.

Motor apparatus of the organ of vision

The eye, in order to respond in a timely manner to stimuli, must be mobile. Three pairs of oculomotor muscles correspond to the motion of the visual apparatus : two pairs of straight and one oblique muscles . These muscles, perhaps, are the fastest in the human body. Controls eyeball movements of the oculomotor nerve. He connects with the nervous system four of the six eye muscles, ensuring their adequate work and coordinated eye movements. If the oculomotor nerve for some reason ceases to function normally, it manifests itself in various symptoms: strabismus, omission of the eyelid, duplication of objects, dilatation of the pupil, accommodation disorders, protrusion of the eyes.

Eye protection systems

Continuing such a voluminous topic as the structure and functions of the visual analyzer, it is impossible not to mention those systems that guard it. The eyeball is located in the bone cavity - the eye socket, on the cushioning fat pad, where it is reliably protected from impact.

In addition to the eye socket, the protective apparatus of the organ of vision includes the upper and lower eyelids with eyelashes. They protect the eyes from getting from the outside of various objects. In addition, the eyelids help to distribute a tear fluid uniformly over the eye surface, and remove the smallest dust particles when the cornea flashes. Eyebrows, too, to some extent perform protective functions, protecting the eyes from the sweat from the forehead.

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

Further processing and final processing of information

The conductor section of the analyzer consists of a pair of optic nerves that come out of the eye sockets and enter the special channels in the cavity of the skull, forming a further incomplete intersection, or a chiasm. Images from the temporal (external) part of the retina remain on the same side, and from the inner, nasal - cross and are transmitted to the opposite side of the brain. As a result, it turns out that the right fields of view are processed by the left hemisphere, and the left ones by the right. Such an intersection is necessary for the formation of a three-dimensional visual image.

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

So, the structure and functions of the visual analyzer are such that violations on any of its sections, whether it is the perceiving, conducting or analyzing zones, entail a malfunction of its operation as a whole. It is a very multifaceted, subtle and perfect system.

Violations of the visual analyzer - innate or acquired, - in turn, lead to significant difficulties in understanding reality and limiting opportunities.