Myelin

Myelin ensheathes the nerve fibers in a spiral lamellar fashion, promoting a faster and more effective conduction of nervous impulses along the nerve fibers. It is produced by the oligodendrocytes during development of the brain and spinal cord and maintained by them after completion of myelination (Fig. 2.10). The major chemical components of myelin are lipids, which constitute about 70% to 85%. The sphingolipids and cholesterol are the most important of these. The remaining 15% to 30% of myelin consists of proteins; among them, myelin basic protein, proteolipid protein, and

Holmes Stain Axons

FIGURE 2.10

Myelin. A. Schematic drawing of axons, myelin sheaths, and oligodendrocytes. B. Light microscopic picture showing longitudinally oriented myelin sheaths (stained blue) along nerve fibers (stained black; Holmes stain). C. Swelling and breaking up of myelin sheaths (LFB-eosin). D. Disintegration of myelin into small oil-red O-positive lipid globules.

TABLE 2.6.

FIGURE 2.10

Myelin. A. Schematic drawing of axons, myelin sheaths, and oligodendrocytes. B. Light microscopic picture showing longitudinally oriented myelin sheaths (stained blue) along nerve fibers (stained black; Holmes stain). C. Swelling and breaking up of myelin sheaths (LFB-eosin). D. Disintegration of myelin into small oil-red O-positive lipid globules.

TABLE 2.6.

Chemical Composition of Central Myelin

Lipids 70%-85% Sphingolipids:

Sphingomyelin: phospholipid Cerebroside: glycolipid (galactose) Sulfatide: cerebroside sulfate ester

Cholesterol

Proteins 15%-30% Myelin basic protein Myelin proteolipid protein Myelin-associated glycoprotein Myelin oligodendrocyte-glycoprotein myelin oligodendrocyte-glycoprotein are particularly important because of their antigenic role in autoimmune diseases (Table 2.6).

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