Definition of "myelin" [my•e•lin]

• A white fatty material, composed chiefly of lipids and lipoproteins, that encloses certain axons and nerve fibers. Also called medulla. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "For the first time researchers at the Krembil Neuroscience Centre, Toronto Western Hospital have successfully transplanted adult spinal cord stem cells into mice and rats to produce the protective cover, known as myelin, which is necessary to insulate the nerves in the central nervous system."
• "They have also been trying to figure out why the patients with multiple sclerosis lose the protective coating, called myelin, surrounding their axons, the part of the nerve cell that conducts electrical impulses."
• "David Van Essen Washington University scientists use MRI scanning of a substance called myelin to find brain-cell branches."