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.

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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

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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.

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Other Word Forms

• myelinic adjective

Etymology

Origin of myelin

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

Example Sentences

Multiple sclerosis occurs when the immune system mistakenly attacks myelin, the protective layer surrounding nerve fibers in the brain and spinal cord.

From Science Daily • Feb. 6, 2026

Oligodendrocytes, the cells that produce myelin to insulate nerve fibers, expressed fewer genes required for maintaining and regenerating the myelin sheath.

From Science Daily • Nov. 24, 2025

Their findings show that the immune system begins attacking the brain's protective myelin sheath -- the fatty covering that insulates nerve fibers -- much earlier than scientists once believed.

From Science Daily • Oct. 21, 2025

It not only stimulated myelin repair but also helped regulate immune activity, a critical balance for MS therapies.

From Science Daily • Oct. 11, 2025

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

From "The 57 Bus" by Dashka Slater