Myelin Sheath

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myelin sheath

[′mī·ə·lən ′shēth]
An investing cover of myelin around the axis cylinder of certain nerve fibers.

Myelin Sheath


(medullary substance; medullary sheath), the sheath enclosing the medullated nerve fibers. The outside of the myelin sheath is covered with a plasma membrane of the Schwann cell; inside, it borders the surface membrane of the axon—the axolemma.

It is believed that the myelin sheath consists of myelin, which includes biomolecular layers of lipides (a phosphatide-cholesterol complex and other chemical components) and coaxially distributed monomolecular layers of protein. The myelin sheath forms as a result of the envelopment of the nerve-cell process by Schwann cells. In the vicinity of the nodes of Ranvier, the myelin sheath is interrupted; the area between any two nodes is formed by a single Schwann cell. The myelin sheath prevents the scattering of nerve impulses and their transfer to other nerve fibers. Impulses are conducted more rapidly in medullated nerve fibers than in nonmedullated ones.

References in periodicals archive ?
Because the mice did not express Lkb1 in myelin forming glial cells, this allowed scientists to analyze its role in glial cell metabolism and formation of the myelin sheath coating.
Plus, say the scientists, these tiny tubes resemble myelin sheaths, which surround and protect neuron extensions in living organisms.
Polar capping of immunoglobulin G (IgG) on macrophages engaged in active myelin phagocytosis; (13) the presence of large numbers of plasma cells in subacute plaques; the identification of immunoglobulin and complement products on degenerating myelin sheaths in acute lesions; (14,15) and, most recently, evidence of dramatic clinical and radiological efficacy of the monoclonal antiCD20 antibody, rituximab, in relapsing MS (16) support the notion that humoral factors play an important role in the immunogenesis of the disease.
In MS, the patients' immune systems turn on their own central nervous systems, stripping the protective myelin sheaths from nerve fibers and leading to problems with vision, balance, and coordination.
The nerves or neurones are the wiring and the myelin sheath is the plastic coat around them.
MCT-125 targets fatigue associated with MS, an autoimmune disease in which immune cells attack and destroy the myelin sheath protecting neurons in the brain and spinal cord.
The money is going to a Cambridge University research project which aims to find a way of repairing the central nervous system's myelin sheath, that is damaged when MS is contracted.
But the overdose also ate away at the myelin sheath that protects the spinal cord.
I have multiple system's atrophy, one of the illnesses which directly attacks the myelin sheath of the brain and central nervous system.
In this disorder the antibodies destroy the myelin sheath that surrounds the peripheral motor neurons and cause inflammation of the axons of the affected nerve cells.
In particular, differences were marked in genes involved in compaction and maintenance of the myelin sheath, and in aptosis and survival of oligodendrocytes.
Waxman's early research showed that when the axon's protective myelin sheath is damaged, as happens in MS, the exposed parts of the axon don't contain enough sodium channels to power nerve conduction.