Optic nerve myelination

Sivron T, Schwab ME, Schwartz M (1994) Presence of growth inhibitors in fish optic nerve myelin Postinjury changes. J Comp Neurol 343 237-246. 

The functional significance of myelin is revealed by the neurological deficits observed in patients with multiple sclerosis. This disorder is caused by the demyelination of neurons in the brain, spinal cord, and optic nerve. The loss of myelin disrupts the normal conduction of impulses along the axons of these neurons and results in weakness, numbness, loss of bladder control, and visual disturbances. 

Myelinating oligodendrocytes have been studied extensively [5,30] (see Ch. 4). Examination of the CNS during myelinogenesis (Fig. 1-15) reveals connections between the cell body and the myelin sheath [31] however, connections between these elements have never been demonstrated in a normal adult animal, unlike the PNS counterpart, the Schwann cell. In contrast to the Schwann cell (see below), the oligodendrocyte is capable of producing many internodes of myelin simultaneously. It has been estimated that oligodendrocytes in the optic nerve produce... 

After the axons enter the optic nerve, each fiber is encapsulated with a myelin sheath, formed by a class of cells called oligodendrocytes this sheath decreases the membrane conductance of the axons, increasing the conduction velocity and the length over which impulses can be conducted without severe attenuation. Only at the so-called Ranvier nodes is the myelin sheath interrupted, allowing the impulses to be reinforced by virtue of the gating properties of the local membrane. 

Several disorders may mimic glaucomatous ONH and/or visual field changes. Those that resemble structural glaucomatous optic neuropathy or interfere wdth assessment of glaucomatous cupping include optic disc anomalies, tilted discs, optic nerve drusen, optic nerve pits, optic nerve colobomas, myelinated nerve fibers, ischemic optic neuropathy and optic atrophy. 

The retina also contains three other types of gUa astrocytes, oligodendrocytes and microglia. Retinal astrocytes are located primarily in the NFL and oligodendrocytes form the myelin sheath of axons in the optic nerve. Hematopoetically derived microglia are small stellate cells that, when quiescent, associate with inner retinal blood vessels. 

Wong EV, David S, Jacob MH, Jay DG (2003) Inactivation of myelin-associated glycoprotein enhances optic nerve regeneration. J Neurosci 23 3112-3117. 

Lang DM, Rubin BP, Schwab ME, Stuermer CA (1995) CNS myelin and oligodendrocytes of the Xenopus spinal cord—but not optic nerve—are nonpermissive for axon growth. J Neurosci 15 99-109. 

Stoll G, Trapp BD, Griffin JW (1989) Macrophage function during Wallerian degeneration of rat optic nerve Clearance of degenerating myelin and la expression. 1 Neurosci 9 2327-2335. 

After exposure to 3300 ppm tellurium in the diet for 5 months, rats were markedly impaired in their ability to learn a sequence of behavioral tasks. The administration of 500-3000 ppm tellurium through the diet to pregnant rats resulted in a high incidence of hydrocephalic offspring. Neonatal rats exposed to tellurium via the mother s milk from the day of birth until killing at 7, 14, 21, or 28 days of age developed Schwann cell and myelin degeneration in the sciatic nerves at each age studied. In the central nervous system (CNS), hypomyelination of the optic nerves was demonstrated at 14, 21, and 28 days of age. 

Maxwell, W. L., McCreath, B. J., Graham, D. I., and Gennarelli, T. A., Cytochemical evidence for redistribution of membrane pump calcium-ATPase and ecto-Ca-ATPase activity, and calcium influx in myelinated nerve fibres of the optic nerve after stretch injury, J. Neurocytol., 24, 925, 1995. 

Liu, K. M. and Shen, C. L., Ultrastructural sequence of myelin breakdown during Wallerian degeneration in the rat optic nerve, Cell Tissue Res., 242, 245, 1985. 

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