From Big Medical Encyclopedia

VISUAL ANALYZER — the complex system of the optical and oculomotor centers and their bonds providing perception, the analysis and integration of visual irritations.

3. and. consists of the peripheral department which is turning on the photoreceptor device of a retina of an eye, an optic nerve and a visual tract (see. Eye , Visual centers, ways , Optic nerve ), and the central (brain) department combining the subcrustal and trunk centers, and also visual area of bark of hemicerebrums. Subcrustal educations 3. and. the lateral cranked body and a pillow of a thalamus are (see. Thalamus ), upper hillocks of a roof of a mesencephalon — chetverokholmiya (see). The visual area of bark of big hemispheres consists of the perceiving 17th field of primary (area striata) and secondary (ekstrastriarny) 18 and 19 fields (see. Very tectonics of a cerebral cortex , Brain , Cerebral cortex ).

3. and. represents a part of the complete functional system connected with many other formations of a brain responsible for irregular shapes of communication visual and other types of information which are the cornerstone of visual recognition, or a gnozis (see. Agnosia ), and also preservation and maintenance of a pose on the basis of vision. Combined activity 3. and. it is provided with broad system of its bonds with a reticular formation of a brainstem, a hypothalamus, various areas of a cerebral cortex. Also other areas of a cerebral cortex participate in the act of sight parietal, temporal, motor, frontal, limbic. The nature of participation of each of these structures is rather specific that promotes ensuring huge range of changes of sensitivity 3. and. depending on degree of illumination, distance to a certain subject, biol, the importance of an irritant and other conditions. Especially defiantly it is shown at a so-called orientative reflex (see. Approximate and research reaction ), caused by inclusion first of all of a reticular formation. Important, though also a little studied, a role in regulation of activity 3. and. belongs to its numerous corticofugal bonds.

3. and. plays a huge role in life of the majority of animals and the person, providing perception of information on various objects and properties of the environment — illumination, a form, size, color, the direction of the movement, about distance to a subject and its space ratios with other objects. Vision is the complex process forming as for pulse counting from effect of light on photoreceptors of a retina of an eye and as a result of proprioceptive irritations of its motive device — muscles of an eyeglobe, iris, an akkomodatsionny (ciliary) muscle.

To the central departments 3. and. the layered arrangement of neurons similar to the perceiving surface of a retina of an eye is peculiar (see. Retina ). The number of nervous elements and their interrelations progressively increases from the periphery to the central departments 3. and. The principle of progressive divergence of visual impulses is combined with the principle of convergence of visual excitement from neurons of a retina of both eyes (binocular interaction) on the same neural complexes — first of all in cortical department Z.a.

For 3. and. also retinotopichesky projection when certain points of a retina are projected on the relevant departments of different levels of the visual analyzer is characteristic. In the field 17 the space continuity of these projections is carried out; less accurate character of projections takes place and in ekstrastriarny visual fields (18 and 19). Svetooptichesky department 3. and. — complex multichannel system, each of channels the cut shall have the functional specifics. Perception of rather simple properties of visual signals is carried out by means of the receptive zones organized in systems of vertically located complexes (columns) of cortical neurons of the 17th field. More difficult complexes of visual signals are perceived by receptive fields 18 and 19.

Partial damage of striatal bark or a rupture of its some afferent bonds with a lateral cranked body is followed by loss of this or that part of a field of vision (see. Scotoma ). At damage of one of hemicerebrums there is a loss of a half of a field of vision (see. Hemianopsia ). At the same time a part of the central sight remains, and at patients the tendency to supplement to whole the familiar objects getting on their «blind» field is observed.

Bilateral destruction of cortical department 3. and. at the highest mammals (dogs, monkeys) or extensive damages of an occipital share at the person lead to loss of subject sight at preservation of ability to distinguish intensity of lighting, and also, perhaps, and contours of objects. These properties of vision are a prerogative of subcrustal and trunk departments 3. and.

The central motive mechanisms of vision — the mechanism of coordination of movements of eyeglobes, convergences of visual axes, reflex regulation of diameter of a pupil — ensure the coordinated work 3. and. in general. The special role in these mechanisms belongs to upper hillocks of a roof of a mesencephalon, pretektalny area, the cortical centers of the movement of eyes, and also kernels and conductors of third cranial nerves. The device of oculomotor function, thus, is generally structurally isolated from svetooptichesky department 3. and.

Value 3. and. for various representatives of fauna not unambiguously also depends on their way of life. Such features of sight as its sharpness, distinguishing of flowers, night or day vision and other, were reflected definitely in structure and chemism of peripheral and central departments 3. and. The acute eyesight and ability to distinguishing of flowers are characteristic of the majority of birds and many primacies, at dogs this feature is expressed more weakly. Distinctive opportunities 3. and. at the person brightness and forms of objects is rather high concerning color. Ability to the most difficult synthesis visual and other perceptions, created in the course of long social development — as a result of work and the articulate speech is especially developed at the person in comparison with animals.

Dysfunction 3. and. — see. Sight, pathology .

Bibliography: Kononova E. P. Anatomy and physiology of occipital shares, M., 1926; Skrebitskiyv. G. Regulation of carrying out excitement in the visual analyzer, M., 1977; Somyen Dzh. Coding of touch information in a nervous system of mammals, the lane with English, M., 1975; Physiology of touch systems, under the editorship of A.S. Batuyev, L., 1976; Sh to about l N and k-Ya p r about with E. G. Neurons and interneural bonds, visual analyzer, L., 1965.

O. S. Adrianov.