medullary sheath

American  

noun

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

2. Anatomy. myelin sheath.

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medullary sheath British  

noun

1. anatomy a myelin layer surrounding and insulating certain nerve fibres

2. a layer of thick-walled cells surrounding the pith of the stems of some higher plants

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Etymology

Origin of medullary sheath

First recorded in 1840–50

Example Sentences

See Examples For:

medullary sheath

Surrounding the axis cylinder is a thick, whitish-looking layer, known as the medullary sheath, and around this is a thin covering, called the primitive sheath, or neurilemma.

From Physiology and Hygiene for Secondary Schools by Walters, Francis M.

MS, medullary sheath, the dark, irregular ring just inside the bundles.

From Wood and Forest by Noyes, William

Axons without the medullary sheath are found in the sympathetic nerves.

From Physiology and Hygiene for Secondary Schools by Walters, Francis M.

This core is surrounded by the white substance of Schwann, or medullary sheath, which gives the nerve its characteristic ivory-white appearance.

From A Practical Physiology by Blaisdell, Albert F.

It will help in understanding the peripheral system to remember that a nerve consists of a bundle of neurone fibers each wrapped in its medullary sheath and sheath of Schwann.

From The Mind and Its Education by Betts, George Herbert