my·e·lin, my·e·line n. Physiol. Chem. (a) A soft white substance constituting the medullary sheaths of nerve fibers, and composed mainly of cholesterin, lecithin, cerebrin, protein, and some fat. (b) One of a group of phosphorized principles occurring in nerve tissue, both in the brain and nerve fibers.
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myeline
n : a white fatty substance that forms a medullary sheath around
the axis cylinder of some nerve fibers [syn: myelin, medulla]