optic nerve(redirected from CN II)
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Related to CN II: Cranial nerves, CN III
optic nerve:see visionvision,
physiological sense of sight by which the form, color, size, movements, and distance of objects are perceived. Vision in Humans
The human eye functions somewhat like a camera; that is, it receives and focuses light upon a photosensitive receiver, the retina.
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(nervus opticus), the second pair of cranial nerves, along which visual stimuli received by the sensory cells of the retina are transmitted to the brain.
The optic nerve is not a typical cranial nerve in structure, but is like brain matter transported to the periphery and connected with the nuclei of the diencephalon, and through them also with the cortex of the large hemispheres. The optic nerve originates in the ganglial cells of the retina. Processes of these cells gather into the optic disk (or papilla), which is located 3 mm closer to the middle from the posterior pole of the eye. Farther on, the bundles of nerve fibers penetrate the sclera in the region of the lamina cribrosa and are surrounded by meningeal structures, forming a compact nerve trunk. Located among the bundles of fibers of the optic nerve are the central artery of the retina and the analogous vein. Together with the ophthalmic artery, the optic nerve passes into the cranial cavity through the optic canal, which is formed by a small wing of the sphenoid bone. Within the cranial cavity, the optic nerve goes from each eye toward the posterior and closer to the middle for about 1 cm, and then approaches the optic nerve of the opposite side over the sella turcica of the sphenoid bone; anterior to the hypophysis the optic chiasma is formed, where there is a crossover only of the axons of the cells of the nasal half of the retina. After the chiasma, the optic nerve continues into the optic tracts.
V. V. KUPRIIANOV