myelin sheath

myelin sheath

n.

The insulating envelope of myelin that surrounds the core of a nerve fiber or axon and that facilitates the transmission of nerve impulses, formed from the cell membrane of the Schwann cell in the peripheral nervous system and from oligodendroglia cells. Also called medullary sheath.

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Myelin sheath

The cover that surrounds many nerve cells and helps to increase the speed by which information travels along the nerve.

Mentioned in: Acoustic Neuroma

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myelin sheath,

a segmented fatty lamination composed of myelin that wraps the axons of many nerves in the body. The usual thickness of the myelin sheath is between 200 and 800 μm. Various diseases such as multiple sclerosis can destroy myelin wrappings.

Myelin sheath

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sheath [shēth]

a tubular case or envelope.

arachnoid sheath the delicate membrane between the pial sheath and the dural sheath of the optic nerve.

carotid sheath a portion of the cervical fascia enclosing the carotid artery, internal jugular vein, vagus nerve, and sympathetic nerves supplying the head.

connective tissue sheath of Key and Retzius endoneurium.

crural sheath femoral sheath.

dural sheath the external investment of the optic nerve.

femoral sheath the fascial sheath of the femoral vessels.

Henle's sheath endoneurium.

lamellar sheath the perineurium.

medullary sheath myelin sheath.

myelin sheath (nerve sheath) the sheath surrounding the axon of myelinated nerve cells, consisting 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 the plasma membrane of oligodendrocytes. It is interrupted at intervals along the length of the axon by gaps known as nodes of Ranvier. Myelin is an electrical insulator that serves to speed the conduction of nerve impulses (see saltatory conduction).

pial sheath the innermost of the three sheaths of the optic nerve.

root sheath the epidermic layer of a hair follicle.

sheath of Schwann neurilemma.

synovial sheath synovial membrane lining the cavity of a bone through which a tendon moves.

tendon sheath a lubricated fibrous or synovial layer of tissue in which the tendon is housed and through which it moves.