from The Century Dictionary.
- noun Same as
from Wiktionary, Creative Commons Attribution/Share-Alike License.
- noun neurology the outermost
nucleated cytoplasmiclayer of Schwann cellsthat surrounds the axonof the neuron.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- noun thin membranous sheath around a nerve fiber
Sorry, no etymologies found.
Each branch receives tubular sheaths from the dura mater and pia mater, the former being lost in the periosteum of the nose, the latter in the neurolemma of the nerve.
When the nerve fiber approaches its termination, the medullary sheath suddenly disappears, leaving only the axis-cylinder surrounded by the neurolemma.
The neurolemma or primitive sheath is not interrupted at the nodes, but passes over them as a continuous membrane.
The neurolemma or primitive sheath presents the appearance of a delicate, structureless membrane.
The axis-cylinder is the essential part of the nerve fiber, and is always present; the medullary sheath and the neurolemma are occasionally absent, expecially at the origin and termination of the nerve fiber.
The central portion is named the axis-cylinder; around this is a sheath of fatty material, staining black with osmic acid, named the white substance of Schwann or medullary sheath, which gives to the fiber its double contour, and the whole is enclosed in a delicate membrane, the neurolemma, primitive sheath, or nucleated sheath of Schwann (Fig. 633) 12
The nerve fiber, on approaching the muscular fiber, suddenly loses its medullary sheath, the neurolemma becomes continuous with the sarcolemma of the muscle, and only the axis-cylinder enters the muscular fiber.
These nuclei are believed to be in connection with a delicate sheath corresponding with the neurolemma of the medullated nerve fiber.
If the fiber be treated with silver nitrate the reagent penetrates the neurolemma at the nodes, and on exposure to light reduction takes place, giving rise to the appearance of black crosses, Ranviers crosses, on the axis-cylinder.
Each nerve cell has a nucleated sheath which is continuous with the neurolemma of the nerve fiber with which the cell is connected.