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about Optic Nerve
The optic nerve, also known as cranial nerve II, is a paired nerve that transmits visual information from the retina to the brain. The optic nerve is derived from optic stalks during the seventh week of development and is composed of retinal ganglion cell axons and glial cells.
In humans, the optic nerve extends from the optic disc to the optic chiasmand continues as the optic tract to the lateral geniculate nucleus, pretectal nuclei, and superior colliculus.
The optic nerve is the second of twelve paired cranial nerves and is technically part of the central nervous system, rather than the peripheral nervous system because it is derived from an out-pouching of the diencephalon (optic stalks) during embryonic development. As a consequence, the fibers of the optic nerve are covered with myelin produced byoligodendrocytes, rather than Schwann cells of the peripheral nervous system, and are encased within the meninges.
Peripheral neuropathies like Guillain-Barré syndrome do not affect the optic nerve. However, most typically the optic nerve is grouped with the other eleven cranial nerves and considered to be part of the peripheral nervous system.
The optic nerve is ensheathed in all three meningeal layers (dura, arachnoid, and pia mater) rather than theepineurium, perineurium, and endoneurium found in peripheral nerves. Fiber tracts of the mammalian central nervous system (as opposed to the peripheral nervous system) are incapable of regeneration, and, hence, optic nerve damage produces irreversible blindness. The fibres from the retina run along the optic nerve to nine primary visual nuclei in the brain, from which a major relay inputs into the primary visual cortex.
The optic nerve is composed of retinal ganglion cell axons and glial cells. Each human optic nerve contains between 770,000 and 1.7 million nerve fibers, which are axons of the retinal ganglion cells of one retina. In the fovea, which has high acuity, these ganglion cells connect to as few as 5 photoreceptor cells; in other areas of retina, they connect to many thousand photoreceptors.