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MYELIN
Copyright 1993 National Multiple Sclerosis Society

The central nervous system (the brain, spinal cord and optic
nerves) is made up of different components: gray matter, white
matter, and supporting cells. The gray matter contains the cell
bodies of the nerves. White matter contains nerve fibers coated
with a fatty insulation called myelin.

The nerve can be likened to an electrical cable, which is
comprised of a 'wire', the axon which actually transmits the
nerve impulse, and the 'insulator', or myelin sheath.

In the central nervous system, the myelin is produced by special
cells called oligodendrocytes. Schwann cells produce myelin in
the peripheral nervous system. In both instances, the axon is
wrapped by concentric layers of myelin.

The myelin itself is a protein- and lipid-rich membrane which
layers around the nerve and acts as insulation. The myelin is
segmental, and there are small areas or 'nodes' which are
unmyelinated.

Chemical ions pass in and out of the axons and generate
electrical current. This current is conducted down the nerve, and
'jumps' from node to node. The myelin prevents the current from
leaking out of the nerve, acts as an insulator and decreases the
electrical resistance of the nerve, thus helping to insure
efficient conduction of the nerve impulse.

An abnormal autoimmune reaction in MS is believed to initiate an
attack on the myelin, resulting in denuded and scarred areas
along the nerve. Conduction of the nerve impulse is then slowed
or halted, producing neurologic signs and symptoms.

Demyelination can also lead to 'cross-talk' between nerves, or
abnormal nerve-to-nerve signalling, which may also produce
symptoms.

Much of the current research in MS is focused on clarifying the
exact nature of the autoimmune response, trying to stop or slow
it, and searching for factors which will promote remyelination of
the damaged nerves. Remyelination has been shown to occur
spontaneously in some MS lesions, and studies with an animal
model of MS, experimental allergic encephalomyelitis (EAE),
have shown that certain compounds can induce remyelination in the
nerves of these animals.

SOURCE: NMSS Information Resource Center and Library. Compendium
of Multiple Sclerosis Information (CMSI), Rev. ed., New York:
National Multiple Sclerosis Society, c. 1992.
Transmitted:  95-08-24 16:20:03 EDT