myelin sheath

myelin sheath n a layer of myelin surrounding some nerve fibers called also medullary sheath

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the cylindrical covering on the axons of some neurons; it consists of concentric layers of myelin, formed in the peripheral nervous system by the plasma membrane of Schwann cells, and in the central nervous system by oligodendrocytes. It is interrupted at intervals along its length by gaps known as nodes of Ranvier. Myelin is an electrical insulator that serves to speed the conduction of nerve impulses. See also myelinated nerve fibers, under fiber. Called also medullary s.

Medical dictionary. 2011.

Look at other dictionaries:

  • myelin sheath — noun a layer of myelin encasing (and insulating) the axons of medullated nerve fibers • Syn: ↑medullary sheath • Hypernyms: ↑sheath, ↑case • Part Holonyms: ↑medullated nerve fiber, ↑ …   Useful english dictionary

  • myelin sheath — noun Date: 1896 a layer of myelin surrounding some nerve fibers called also medullary sheath …   New Collegiate Dictionary

  • myelin sheath — my′elin sheath n. anat. zool. a discontinuous wrapping of myelin around certain nerve axons, serving to speed nerve impulses to muscles and other effectors • Etymology: 1895–1900 …   From formal English to slang

  • myelin sheath — Anat. a wrapping of myelin around certain nerve axons, serving as an electrical insulator that speeds nerve impulses to muscles and other effectors. See diag. under neuron. [1895 1900] * * * …   Universalium

  • myelin sheath — noun An envelope of myelin that surrounds nerve fibres …   Wiktionary

  • myelin sheath — /maɪələn ˈʃiθ/ (say muyuhluhn sheeth) noun the layer of myelin encasing the axon of a nerve fibre, serving to insulate the nerve and to facilitate nerve impulses …   Australian English dictionary

  • myelin sheath — A fatty material surrounding a nerve fiber …   Dictionary of invertebrate zoology

  • myelin sheath — An insulating layer surrounding vertebrate peripheral neurons, that dramatically increases the speed of conduction. It is formed by specialized Schwann cells, that can wrap around neurons up to 50 times. The exposed areas are called nodes of… …   Dictionary of molecular biology

  • myelin sheath — coating on the axons of nerve cells …   English contemporary dictionary

  • Myelin sheath gap — Drawing of a peripheral nerve axon (labeled axis cylinder ), showing a node of Ranvier along with other features …   Wikipedia

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