noun Biology.
a soft, white, fatty material in the membrane of Schwann cells and certain neuroglial cells: the substance of the myelin sheath.
Also, myeline [mahy-uh-leen] .

1865–70; myel- + -in2

myelinic, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
myelin or myeline (ˈmaɪɪlɪn, ˈmaɪɪˌliːn)
a white tissue forming an insulating sheath (myelin sheath) around certain nerve fibres. Damage to the myelin sheath causes neurological disease, as in multiple sclerosis
myeline or myeline
mye'linic or myeline

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

1867, from Ger. myelin, from Gk. myelos "marrow."
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

myelin my·e·lin (mī'ə-lĭn) or my·e·line (-lĭn, -lēn')

  1. A white fatty material composed chiefly of alternating layers of lipids and lipoproteins that encloses the axons of myelinated nerve fibers.

  2. Droplets of lipid formed during autolysis and postmortem decomposition.

my'e·lin'ic adj.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
myelin   (mī'ə-lĭn)  Pronunciation Key 
A whitish, fatty substance that forms a sheath around many vertebrate nerve fibers. Myelin insulates the nerves and permits the rapid transmission of nerve impulses. The white matter of the brain is composed of nerve fibers covered in myelin.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Britannica


white, insulating sheath composed of fatty materials, protein, and water on the axon of many nerve fibres. The myelin sheath is deposited by Schwann cells in layers surrounding the nerve fibres of the central and peripheral nervous systems of many organisms. The sheath is interrupted at intervals by gaps called nodes of Ranvier; this structure speeds nerve conduction, as impulses jump from node to node in a process known as saltatory conduction.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
In both cases, the yellow-green color corresponds to newly-grown myelin.
As myelin degrades, the fibers cannot conduct electrical impulses.
Without this sheath, made of a substance called myelin, nerve cells eventually
The illness is believed to result from impaired signaling between neurons in
  the brain caused by a reduction in myelin.
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