According to a Wikipedia article about the optic nerve, the optic nerve is the second of twelve paired cranial nerves 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 fibers are covered with myelin produced by oligodendrocytes rather than the Schwann cells of the peripheral nervous system. Similarly, 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. This is an important issue, as fiber 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.
But hold on! According to more recent research, central nervous system neurons do have a limited capability for self-repair and regeneration. Central nervous system axons have been proven to regrow in permissible environments **; therefore, the primary problem to central nervous system axonal regeneration is crossing (or eliminating) the glial scar (which usually forms after injury as a result of debris not being cleared away efficiently enough by the immune system). Here is a link to another Wikipedia article that discusses nerve regeneration in a little more detail: http://en.wikipedia.org/wiki/Nerve_regeneration
In my opinion, many scientists vastly underestimate the body's ability to heal itself, so I expect continued upward revisions regarding the possibilities for optic nerve regeneration.
This drawing of the optic nerve comes from Gray's Anatomy.
** Recknor, J.B. and S.K. Mallapragada, Nerve Regeneration: Tissue Engineering Strategies, in The Biomedical Engineering Handbook: Tissue Engineering and Artificial Organs, J.D. Bronzino, Editor. 2006, Taylor & Francis: New York
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