myelin

American  

[mahy-uh-lin] / ˈmaɪ ə lɪn /

Also myeline

noun

Biology.

1. a soft, white, fatty material in the membrane of Schwann cells and certain neuroglial cells: the substance of the myelin sheath.

---

myelin British  

/ ˈmaɪɪˌliːn, ˈmaɪɪlɪn /

noun

1. 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

---

myelin Scientific  

/ mī′ə-lĭn /

1. 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.

---

Other Word Forms

• myelinic
  adjective

Etymology

Origin of myelin

First recorded in 1865–70; myel- + -in ²

Example Sentences

MS is a disease of the brain and central nervous system, in which the immune system mistakenly attacks the fatty myelin sheath that normally protects the nerves, like insulation around electric wires.

From BBC • May 29, 2026

Damage to myelin is also a defining feature of multiple sclerosis.

From Science Daily • May 27, 2026

These specialized brain cells are responsible for producing and maintaining myelin.

From Science Daily • May 27, 2026

"ATDR is something everyone already has in their body. Our findings suggest that there may be an alternative approach that uses naturally occurring molecules to treat diseases related to myelin damage," he says.

From Science Daily • Apr. 15, 2026

Throughout adolescence, the brain is busily lining important neural pathways with a fatty sheath called myelin.

From "The 57 Bus" by Dashka Slater