Dictionary

myelin sheath

noun

Definition of MYELIN SHEATH

:  a layer of myelin surrounding the axons of some neurons —called also medullary sheath

First Known Use of MYELIN SHEATH

1891

myelin sheath

noun    (Medical Dictionary)

Medical Definition of MYELIN SHEATH

:  the insulating covering that surrounds an axon with multiple spiral layers of myelin, that is discontinuous at the nodes of Ranvier, and that increases the speed at which a nerve impulse can travel along an axon—called also medullary sheath

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