The optic nerve, its structure and functions

The optic nerve belongs to highly specialized nerves and resembles the cerebral cortex in structure. The functions of the optic nerve consist in the transmission of nerve impulses obtained by the action of various light stimuli from the retina of the eye to the visual center of the cerebral cortex.

Optic nerve: structure.

Nerve fibers of the eye retina combine into one optic nerve. It consists of four sections: intraocular, intracanular, intraorbital and intracranial. The intraocular department is a disc with a diameter of about 1.5 mm. The orbital part has a length of about 3 cm. The optic nerve has a length of 5-6 mm in the bone channel and 4-17 mm in the intracranial canal.

The location of nerve endings in various areas of the retina is constructed according to a certain structure. Thus, when approaching the disk, the layer of nerve fibers has a large thickness, while the nerve fibers in the disk are curved at right angles, forming the intraocular compartment of the optic nerve.

The optic nerve starts from the disk and has an ending in the chiasm. The optic nerve in an adult has a length of 35 to 55 mm. It is covered with three medullary membranes: firm, soft and arachnoid. The space between these shells is filled with a special liquid with a complex chemical composition.

The visual fibers from both eyes exit into the cranial cavity, where they join in the area of the Turkish saddle. The place of their unification is called chiasma. It partially overlaps the visual fibers. Crossing is subject to those fibers that come from the inner parts of the retina. These crossovers are very important for the correct diagnosis of certain diseases. After crossing, visual tracts are formed, which at the base of the brain skirt around its pedicle and end in the geniculate bodies, the front quadruple, and also in the posterior region of the visual hillock. Cranial bodies are most important in the transmission of visual impulses to the cerebral cortex. Those fibers that terminate in the visual hillock effect reflex regulation of visceral and somatic reflexes. And the front quadruple is used to transmit reflexes of the pupils. The visual fibers pass to the nuclei of the oculomotor nerve, in which they enter the eye, ending in the musculature of the iris.

Pathological processes that develop in the optic nerve have a close relationship with its structure. Because of the large number of capillaries that are contained in the septum and surround the optic nerve, as well as hypersensitivity to toxins, conditions are created for toxic effects on the visual nerve endings and infectious diseases. When the intraocular pressure rises, the disc becomes the most vulnerable place, as a result of which it is punctured and formed in the case of glaucoma. High intracranial pressure delays the outflow of fluid in the interbloc space, resulting in compression of the nerve and swelling of the interstitial substance contained therein.

The disc is also adversely affected by hydrodynamic and hemodynamic changes, which lead to a decrease in intraocular pressure. Any changes in the optic nerve always lead to impaired peripheral or central vision, and there may be a deterioration in twilight vision and color differences. Diseases related to the optic nerve are degenerative, allergic or inflammatory. Sometimes there are tumors and abnormalities in the development and structure of the optic nerve.