myelin

noun

my·​e·​lin ˈmī-ə-lən 

: 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

ˌmī-ə-ˈli-nik 

adjective

Examples of myelin in a Sentence

Recent Examples on the Web

Without myelin, signals that would normally rapidly fire across nerves are slowed or blocked. — Kaitlin Sullivan, NBC news, 15 Mar. 2026

Without proper myelin, nerve signals slow down or get lost, damaging the brain’s white matter. — Lucy Notarantonio, MSNBC Newsweek, 2 Nov. 2025

Over time, learning something new may also help thicken myelin, which is the layer of protein coating the neurons in your brain. — Ayana Underwood, SELF, 15 Sep. 2025

White matter, so named because of a pale, fatty substance called myelin that wraps the bundles of nerves, carries information between gray matter areas like highways in the brain. — Christopher M. Filley, The Conversation, 3 Feb. 2026

Word History

Etymology

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

Phrases Containing myelin

• myelin sheath

Rhymes for myelin

• sphingomyelin

Kids Definition

myelin

noun

my·​elin

ˈmī-ə-lən

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

Medical Definition

myelin

noun

my·​e·​lin ˈmī-ə-lən 

: 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

ˌmī-ə-ˈlin-ik 

adjective