The visual analyzer - the system of bodies consisting of the receptor device (eyes), the carrying-out ways, some sites of bark of a brain. It provides perception to 90% of information arriving from the world around.
Main departments
The system of bodies forming the visual analyzer consists of several departments:
- peripheral (includes retina receptors);
- conduction (presented by an optic nerve);
- central (center of the visual analyzer).
Thanks to peripheral department the possibility of collecting visual information is provided. Through a conduction part it is given to brain bark where there is its processing.
Structure of eyes
Eyes are located in eye-sockets (deepenings) of a skull, consist of eyeballs, the auxiliary device. The first have the sphere form to dia. up to 24 mm, about 7-8 g weigh. They are formed by several covers:
- Sclero – an external cover. Opaque, dense, includes blood vessels, the nervous terminations. A front part is connected to a cornea, back – to a retina. Sclero gives the form to eyes, without allowing them to be deformed.
- Vascular cover. Thanks to it nutrients arrive to a retina.
- It is formed by cells of photoreceptors (sticks, flasks), producing substance rhodopsin. It transforms energy of light to electric, further it is distinguished by brain bark.
- Transparent, without blood vessels. There is it in front department of an eye. In a cornea light refracts.
- Iris of the eye (iris). Formed by muscle fibers. They provide reduction of the pupil which is in the center of an iris. The amount of light getting into a retina is quite so regulated. Color of an iris of eyes is provided with concentration in it a special pigment.
- Ciliary muscle (ciliary corbel). Its function - ensuring ability of a crystalline lens to focus a look.
- Crystalline lens. A transparent lens thanks to which the distinct sight is provided.
- Vitreous body. It is presented by the gel transparent substance which is in eyeballs. Through a vitreous body light gets from a crystalline lens to a retina. Its function – formation of steady eye shape.
Auxiliary device
The auxiliary device of eyes is formed for centuries, eyebrows, plaintive muscles, eyelashes, motive muscles. It provides protection of eyes and their movement. Behind they are surrounded with fat cellulose.
Over eye-sockets there are eyebrows protecting eyes from liquid hit. Eyelids promote moistening of eyeballs, provide protective function.
Eyelashes belong to the auxiliary device, at irritation they provide a protective reflex of a smykaniye a century. It is also necessary to mention a conjunctiva (mucous membrane), it covered eyeballs in a front part (except a cornea), eyelids from within.
In the upper outer (lateral) edges of eye-sockets there are plaintive glands. They produce the liquid necessary for ensuring transparency of a cornea and its purity. Also it protects eyes from drying. Thanks to blinking a century plaintive liquid can be distributed on the surface of eyes. Protective function is also provided by 2 locking reflexes: corneal, pupillary.
The eyeball moves with the help, 6 muscles, 4 call straight lines, and 2 - slanting. One pair of muscles provides movements up-down, the second couple provides movements to the left-to the right. The third pair of muscles gives the chance to eyeballs to rotate rather optical axis, eyes can look in various directions, reacting to irritants.
Optic nerve, its functions
Considerable part of the carrying-out way is formed by an optic nerve 4-6 cm long. It begins on a back pole of eyeballs where it is presented by several nervous shoots (the so-called disk of an optic nerve (DON). It passes and in an eye-socket, around it there are brain covers. A small part of a nerve is located in a front cranial pole where it is surrounded with brain tanks, a soft cover.
Main functions:
- Transfers impulses from receptors in a retina. They pass to subcrustal structures of a brain, and from there to bark.
- Provides feedback by signal transmission from brain bark to eyes.
- Is responsible for fast reaction of eyes to irritants from the outside.
Over the place of an entrance of a nerve (opposite to a pupil) there is a yellow spot. It is called the site of the highest visual acuity. The painting pigment which concentration is quite considerable is a part of a yellow spot.
Central department
The place of localization of the central (cortical) department of the central analyzer - in an occipital share (back part). In visual zones of bark processes of the analysis come to an end, and then recognition of an impulse - creation of an image begins. Conditionally allocate:
- Kernel of the 1st alarm system (the place of localization - around a shporny furrow).
- Kernel of the 2nd alarm system (the place of localization - around the left angular crinkle).
Across Brodman the central department of the analyzer is located in fields 17, 18, 19. If field 17 is struck, approach of a physiological blindness is possible.
Functions
The main functions of the visual analyzer – perception, carrying out, processing of information obtained through organs of vision. Thanks to it the person has an opportunity to perceive surrounding with way of transformation to visions of the beams which are reflected from objects. The day sight is provided with the central visual and nervous office, and twilight, night - peripheral.
Mechanism of perception of information
The mechanism of operation of the visual analyzer is compared to operation of the TV. Eyeballs can be associated with the antenna accepting a signal. Reacting to an irritant, they are transformed to an electrowave which is transferred to sites of bark of a brain.
The conduction part consisting their nervous fibers is a television cable. And the TV is served by the central department which is in brain bark. It processes signals, transferring them to images.
In cortical department of a brain there is a perception of difficult objects, the form, the size, remoteness of objects are estimated. As a result the obtained information unites in the general picture.
So, light is perceived by a peripheral part of eyes, passing to a retina through a pupil. In a crystalline lens it refracts and will be transformed to an electrowave. On nervous fibers it arrives to bark where the obtained information is deciphered and estimated, and then is decoded in the visual picture.
The image is perceived by the healthy person in a three-dimensional look that is provided with existence of 2 eyes. From the left eye the wave goes to the right hemisphere, and from right – to left. Connecting, waves give the accurate image. Light refracts on a retina, images come to a brain turned, and after they will be transformed to the form habitual for perception. At any violation of binocular sight of people sees 2 pictures at once.
It is supposed what newborns surrounding sees in the turned look, and images are represented in black-and-white color. In 1 year children perceive the world almost like adult. Formation of organs of vision comes to an end by 10-11 years. After 60 years the visual functions worsen as there comes the natural wear of cages of an organism.
Violations of operation of the visual analyzer
Malfunction of the visual analyzer becomes the reason of difficulties of perception surrounding. It limits contacts, the person will have less opportunities to be engaged in any type of activity. The reasons of violations divide into congenital, acquired.
Carry to congenital:
- the negative factors operating on a fruit in the pre-natal period (infectious diseases, metabolism violations, inflammatory processes);
Acquired:
- some infectious diseases (tuberculosis, syphilis, smallpox, measles, diphtheria, scarlet fever);
- hemorrhages (intra cranial, intraocular);
- injuries of the head, eye;
- diseases which are followed by increase in intraocular pressure;
- violations of communications between the visual center, a retina;
- central nervous system diseases (encephalitis, meningitis).
Congenital violations are shown mikroftalmy (reduction of the sizes of the 1st or both eyes), anoftalmy (bezglaziy), a cataract, retina dystrophy. Carry a cataract, glaucoma which break function of visual bodies to the acquired diseases.