American Heritage® Dictionary of the English Language, Fourth Edition
- n. The insulating envelope of myelin that surrounds the core of a nerve fiber or axon and facilitates the transmission of nerve impulses. In the peripheral nervous system, the sheath is formed from the cell membrane of the Schwann cell and, in the central nervous system, from oligodendrocytes. Also called medullary sheath.
- n. a layer of myelin encasing (and insulating) the axons of medullated nerve fibers
“One of the cell types injured by high levels of the protein IL-6 includes oligodendrocytes, which help to produce the protective myelin sheath around nerve cells.”
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