Visual Pathways

The visual pathways (tertiary apparatus) are the nerve pathways of the central nervous system, starting from the retina and containing over 2 million nerve fibers that ensure the transmission of visual impulses to the cortex of the occipital lobes of the brain along with associative fibers from the subcortical visual centers. These fibers form bundles - visual radiance. Thanks to the visual pathways, vision, clear vision of space, movement of the eyeball, narrowing, expansion and focusing of the visual field, vision with closed eyes are carried out. The optic radiance also includes vasoparasympathetic fibers of the oculomotor nerve and fibers of the sympathetic system. Optic radiance is formed by three interconnected systems: 1) the optic nerve (the fibers of which make up the rod, cone and, to a lesser extent, the ganglion system); 2) posterior communicating branch; 3) the optic nerve’s own optical system, which includes about 2.5 million axons of retinal ganglion cells, which are conventionally divided into pigment (olfactory) fibers, axons of transitional (bipolar), granular (cone) fibers, fibers with large endings, etc. Formation of the optic nerve pathways end in the midbrain and cerebellum, in the thalamus and striatum. When considering the issue of localization of visual functions and physiological characteristics of the visual pathway, a variety of points of view is noted. One of them suggests that primary information processing occurs at the level of photoreceptor cells in the retina. Another point of view is that the information necessary to preserve tactile, tactile, olfactory sensations in fish (primarily in clear, refined water or an aquarium environment) is transmitted by an intermediate conductor along the optic nerve, without decoding in the central apparatus of the visual analyzer located in the anterior brain stem - the central cortex, the visual zone of the cingulate and temporal cortex of the brain. According to the third point of view, the visual pathway in its primary function is most closely connected with the perception of the external world and only after that it directs information to the brain formations. Therefore, despite the different biological significance of the visual function, there is a unified method for studying the functions of the visual parts of the brain and its structures (Chapter 86).

The visual pathway consists of five neurons. The first layer is the retina or photoreceptors. It is made up of sensitive light-sensitive cells called cones, which are responsible for the perception of light and color. They transmit messages through a second neuron, called a ganglion neuron, to a third neuron in the cerebral cortex, where sensations are formed. Each optical image falling on the retina is nothing more than the sum of the luminances of monochrome signals created by various points on the surface of the retina (photoreceptor cones differ in spectral sensitivity and are distributed heterogeneously across the retina). This allows you to encode the detail of light, distinguish the direction of light rays and textures.

When you look at an object with both eyes, the brain receives a binocular image. This ensures normal depth perception and the ability to determine the distance to an object. If we look