medullary sheath

noun

a layer of myelin encasing (and insulating) the axons of medullated nerve fibers

• Syn: ↑myelin sheath

• Hypernyms: ↑sheath, ↑case

• Part Holonyms: ↑medullated nerve fiber, ↑myelinated nerve fiber

• Substance Meronyms: ↑myelin, ↑myeline, ↑medulla

• Part Meronyms: ↑axolemma, ↑Ranvier's nodes, ↑nodes of Ranvier, ↑oligodendroglia, ↑oligodendria

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noun

1. : the layer of myelin surrounding a medullated nerve fiber

2. : the outer layers of smaller usually thick-walled cells that merge into the central pithy part of the core of many plant stems

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1. Bot. a narrow zone made up of the innermost layer of woody tissue immediately surrounding the pith in plants.

2. Anat. See myelin sheath.

[1840-50]

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medullary sheath noun

1. A thin layer surrounding the pith (botany)

2. A whitish fatty membrane which surrounds the axons of the central nervous system in vertebrates and acts as an insulating coat (anatomy)

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Main Entry: ↑medulla

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medullary sheath,

1. a narrow ring comprising the innermost layer of woody tissue that surrounds the pith in certain plants.

2. = myelin. (Cf. ↑myelin)