Darkfield photomicrograph, Human eye optic nerve detail
The second of twelve paired cranial nerves in the human body but is considered to be part of the central nervous system as it is derived from an outpouching of the diencephalon during embryonic development. Consequently, the fibres are covered with myelin produced by oligodendrocytes rather than the Schwann cells of the peripheral nervous system and are encased within the meninges. Therefore the distinction of nerve is technically a misnomer, as the optic system lies within the central nervous system and nerves exist, by definition, within the peripheral nervous system. Therefore peripheral neuropathies like Guillain-Barré syndrome do not affect the optic nerve. 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. Fibre tracks 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, whence a major relay inputs into the primary visual cortex.
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Photo credit: © Scenics & Science / Alamy / Afripics
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Keywords: cones, cortex, darkfield, detail, eye, human, imaging, myelin, nerve, oligodendrocytes, optic, photomicrograph, primary, retina, rods, visual
