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.

syn·o·vi·al ten·don sheath

[TA]

a sheath of synovial membrane enveloping certain of the tendons; it contains a small amount of synovial fluid.

Synonym(s): vagina synovialis tendinis [TA], mucous sheath of tendon, theca tendinis, vagina mucosa tendinis, vaginal synovial membrane

synovial layer of tendon sheath

a thin, slightly redundant, highly vascular connective tissue membrane lining a tendon sheath; consists of visceral and parietal components and produces a viscous lubricating fluid.

Synonym(s): stratum synoviale (vagina synovialis) vaginae tendinis [TA], synovial sheath [TA]

syn·o·vi·al sheaths of fin·gers

(si-nō'vē-ăl shēths fing'gĕrz)

Synovial envelopes that enclose the flexor tendons of the fingers, each extending from the proximal end of the carpal ligament to the base of a distal phalanx.

syn·o·vi·al sheaths of toes

(si-nō'vē-ăl shēths tōz) [TA]

Envelopes similar in structure to the corresponding sheaths of fingers.