The proportion of decussating fibers varies between species, and is correlated with the degree of binocular vision enjoyed by a species.
The optic nerve leaves the orbit (eye socket) via the optic canal, running postero-medially towards the optic chiasm, where there is a partial decussation (crossing) of fibers from the temporal visual fields (the nasal hemi-retina) of both eyes. In the fovea, which has high acuity, these ganglion cells connect to as few as 5 photoreceptor cells in other areas of the retina, they connect to thousands of photoreceptors. 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. The optic nerve is composed of retinal ganglion cell axons and glia. The white circle is the beginning of the optical nerve.
The fibers 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.Ī fundus photograph showing the back of the retina. Therefore, in most mammals, optic nerve damage results in irreversible blindness. Fiber tracts of the mammalian central nervous system have only limited regenerative capabilities compared to the peripheral nervous system. The optic nerve is ensheathed in all three meningeal layers ( dura, arachnoid, and pia mater) rather than the epineurium, perineurium, and endoneurium found in peripheral nerves. However, most typically, the optic nerve is grouped with the other eleven cranial nerves and is considered to be part of the peripheral nervous system. Peripheral neuropathies like Guillain–Barré syndrome do not affect the optic nerve.
As a consequence, the fibers of the optic nerve are covered with myelin produced by oligodendrocytes, rather than Schwann cells of the peripheral nervous system, and are encased within the meninges. The optic nerve has been classified as the second of twelve paired cranial nerves, but it is technically a myelinated tract of the central nervous system, rather than a classical nerve of the peripheral nervous system because it is derived from an out-pouching of the diencephalon ( optic stalks) during embryonic development. In humans, 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 it extends from the optic disc to the optic chiasma and continues as the optic tract to the lateral geniculate nucleus, pretectal nuclei, and superior colliculus. In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain.
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