my·​e·​lin ˈmī-ə-lən How to pronounce myelin (audio)
: a soft white material that forms a thick layer around the axons of some neurons and is composed chiefly of lipids (such as cerebroside and cholesterol), water, and smaller amounts of protein
myelinic adjective

Examples of myelin in a Sentence

Recent Examples on the Web In Emma’s case, the combination of mutations appears to affect her brain’s myelin, the protective sheathing that covers our nerves and brain cells, says Carlos Bacino, a clinical geneticist at the Baylor College of Medicine, a UDN site, and Emma’s physician at Texas Children’s Hospital. Nathaniel Scharping, Discover Magazine, 18 June 2021 An analogy sometimes given is that the nervous system is like the wiring of a lamp, and the myelin like the wiring’s protective sheath; when that sheath wears away, so much can go wrong. Rivka Galchen, The New Yorker, 17 July 2023 To pull that off, axons are insulated with myelin, a fatty substance that speeds transmission. Lydia Denworth, Scientific American, 1 Aug. 2021 Degrading myelin leads to communication difficulties between neurons and their connections with the rest of the body. Kristine Zengeler, Discover Magazine, 10 Dec. 2022 As children become teenagers, the rapid expansion of myelin increasingly joins and coordinates activities in different parts of the brain on a variety of cognitive tasks. Jay N. Giedd, Scientific American, 1 May 2016 Recent investigations are revealing another, more nuanced role for myelin. Jay N. Giedd, Scientific American, 1 May 2016 Researchers today announced progress toward a multiple sclerosis treatment that fights myelin destruction while keeping patients’ immune systems intact. Becky Lang, Discover Magazine, 5 June 2013 Now Fields and others have figured out exactly how glial cells alter myelin, the insulation of our neural wiring, to support the mind’s acquisition of knowledge. Curtis Brainard, Scientific American, 1 Mar. 2020 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'myelin.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


borrowed from German Myelin, from Greek myelós "bone marrow" + German -in -in entry 1 — more at myelo-

Note: The term was introduced by Rudolf virchow in "Ueber das ausgebreitete Vorkommen einer dem Nervenmark analogen Substanz in den thierischen Geweben," Archiv für pathologische Anatomie und Physiologie und für klinische Medicin, 6. Band (1854), p. 571

First Known Use

1866, in the meaning defined above

Time Traveler
The first known use of myelin was in 1866

Dictionary Entries Near myelin

Cite this Entry

“Myelin.” Dictionary, Merriam-Webster, Accessed 6 Dec. 2023.

Kids Definition


: a soft white somewhat fatty material that forms a thick layer around the axons of some neurons

Medical Definition


my·​e·​lin ˈmī-ə-lən How to pronounce myelin (audio)
: a soft white material of lipid and protein that is secreted by oligodendrocytes and Schwann cells and forms a thick sheath about axons see myelin sheath
myelinic adjective

More from Merriam-Webster on myelin

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