The conductive path of the visual analyzer

The light that enters the retina first passes through the transparent light-refracting media of the eyeball: the cornea, the watery moisture of the anterior and posterior chambers, the lens, the vitreous. On the path of the light beam is the pupil. Under the influence of the muscles of the iris, the pupil contracts, then expands. Refractive media (cornea, lens, etc.) direct a beam of light to the most sensitive place of the retina, the place of the best vision is a spot with its central fossa. An important role in this is played by the lens, which with the help of the ciliary muscle can increase or decrease its curvature when seeing a near or far distance. This ability of the lens to change its curvature (accommodation) ensures the direction of the light beam always on the central fossa of the retina, which is in line with the observed object. The direction of the eyeballs towards the object under consideration is provided by the oculomotor muscles, which establish the visual axes of the right and left eyes parallel to the vision or converge them (convergence) when viewing the subject at close range.

The light that penetrates the retina penetrates into its deep layers and causes complex photochemical transformations of visual pigments. As a result, a nerve impulse appears in photosensitive cells (in rods and cones). Then the nerve impulse is transferred to the following neurons of the retina - bipolar cells (neurocytes), and from them to the neurocytes of the ganglionic layer, ganglionic neurocytes. The processes of ganglionic neurocytes are directed toward the disc and form the optic nerve. Enveloped by its own vagina, the optic nerve emerges from the orbit cavity through the optic nerve channel into the cranial cavity and forms a visual crossover on the lower surface of the brain. Not all fibers of the optic nerve cross, but only those that follow from the medial, turned towards the nose of the part of the retina. Thus, the visual path following the chiasm is the nerve fibers of the ganglion cells of the lateral (temporal) part of the retina of the eyeball of its side and the medial (nasal) part of the retina of the eyeball of the other side. That is why if the chiasma is damaged, the functions of carrying out impulses from the medial parts of the retina of both eyes are lost, and if the visual path is damaged - from the lateral part of the retina of the same side and the medial part of the other.

Nerve fibers in the optic tract follow to the subcortical visual centers: the lateral geniculate body and the upper hillocks of the midbrain roof. In the lateral geniculate body, the fibers of the third neuron (ganglionic neurocytes) of the visual pathway terminate and come into contact with the cells of the next neuron. The axons of these neurocytes pass through the subclavian part of the inner capsule, form a visual radiance (radiatio optica) and reach the portion of the occipital lobe of the cortex near the furrow groove, where a higher analysis of visual perception is performed. Part of the axons of ganglion cells does not end in the lateral geniculate body, but passes through it in transit and reaches the upper mound in the handle. From the gray layer of the upper hillock, the impulses enter the nucleus of the oculomotor nerve and its additional nucleus (the nucleus of Yakubovich), from which the innervation of the oculomotor muscles takes place, as well as the muscle contracting the pupil and the ciliary muscle. On these fibers, in response to light stimulation, the pupil narrows (pupillary, papillary, reflex), and the eyeballs turn in the right direction.