Lexic.us

Definition of Medullary sheath

1. Noun. A layer of myelin encasing (and insulating) the axons of medullated nerve fibers.

Medical Definition of Medullary sheath

1. An insulating layer surrounding vertebrate peripheral neurons, that dramatically increases the speed of conduction. It is formed by specialised Schwann cells, that can wrap around neurons up to 50 times. The exposed areas are called nodes of Ranvier: they contain very high densities of sodium channels and action potentials jump from one node to the next, without involving the intermediate axon, a process known as saltatory conduction. This entry appears with permission from the Dictionary of Cell and Molecular Biology (11 Mar 2008)

Lexicographical Neighbors of Medullary Sheath

Literary usage of Medullary sheath

Below you will find example usage of this term as found in modern and/or classical literature:

1. Encyclopaedia Britannica: A Standard Work of Reference in Art, Literature (1907)
"Each fibre consists of three parts : (1) an external sheath or primitive sheath ; (i) within this the medullary sheath or white ..."

2. An American Text-book of Physiology by William Henry Howell (1900)
"in the growth of the cell is the formation of the medullary sheath about ... Not all axones have a medullary sheath, uor is any axone completely medullated. ..."

3. Philosophical Magazine (1805)
"D, Herbaceous prolongation of the medullary sheath passing through the wood and ... E, medullary sheath of a branch• G, Pith. F, medullary sheath of a twig. ..."

4. Medical Record by George Frederick Shrady, Thomas Lathrop Stedman (1897)
"It is only where the nerve has lost its medullary sheath that the nucleus becomes visible. ... The medullary sheath or white substance of Schwann is a soft, ..."

5. Quain's Elements of Anatomy by Jones Quain, Allen Thomson, George Dancer Thane (1882)
"Other breaks of continuity are seen in the medullary sheath (fig. ... In C' ,'B sequence of their presence the medullary sheath almost constantly appears as ..."

6. Journal of Nervous and Mental Disease by Philadelphia Neurological Society, American Neurological Association, Chicago Neurological Society, New York Neurological Association (1884)
"The medullary sheath of almost all nerve-fibres in these preparations was deranged, its fibrillar layer being displaced to form larger or smaller ..."

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