| medullary sheath | <anatomy, neurology> 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. (18 Nov 1997) |
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| root sheath | One of the epidermic layers of the hair follicle: external root sheath is continuous with the stratum basale and stratum spinosum of the epidermis; internal root sheath comprises the cuticle of the internal roots, Huxley's layer, and Henle's layer. (05 Mar 2000) |
| Rouget-Neumann sheath | The amorphous ground substance between an osteocyte and the lacunar or canalicular wall. (05 Mar 2000) |
| microfilarial sheath | The membrane surrounding the embryos of certain blood-borne microfilariae, such as Wuchereria, Brugia, and Loa of humans; thought to be derived from the vitelline membrane. (05 Mar 2000) |
| mitochondrial sheath | The spirally arranged mitochondria in the middle piece of a spermatozoon; may control movement of the tail. (05 Mar 2000) |
| Waldeyer's sheath | The tubular space between the bladder wall and the intramural portion of the ureter as it courses obliquely through this structure; actually a space and not a true sheath. Synonym: Waldeyer's space. (05 Mar 2000) |
| common flexor sheath | The synovial sheath that surrounds the eight tendons of the superficial and deep flexors of the digits of the hand as they pass through the carpal canal; it is commonly continuous with the digital sheath of the little finger. Synonym: vagina communis musculorum flexorum, ulnar bursa. (05 Mar 2000) |
| common peroneal tendon sheath | The sheath that surrounds the tendons of the peroneus longus and brevis muscles in their passage across the ankle. Synonym: vagina tendinum musculorum peroneorum communis, vagina tendinum musculorum fibularium communis. (05 Mar 2000) |
| plantar tendon sheath of peroneus longus muscle | <anatomy> The synovial sheath surrounding the tendon of the peroneus longus in its course across the sole of the foot. Synonym: vagina tendinis musculi peronei longi plantaris. (05 Mar 2000) |
| mucous sheath of tendon | A sheath of synovial membrane enveloping certain of the tendons; it contains a small amount of synovial fluid. Synonym: vagina synovialis tendinis, mucous sheath of tendon, theca tendinis, vagina mucosa tendinis, vaginal synovial membrane. (05 Mar 2000) |
| myelin sheath | <anatomy, neurology> 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. (18 Nov 1997) |
| posterior layer of rectus abdominis sheath | The portion of the sheath of the rectus abdominis muscle that lies posterior to the muscle covering only its upper two-thirds; it is formed by contributions from the aponeuroses of the internal oblique and transversus abdominis muscles; its free inferior margin forms the arcuate line; it is deficient below this, the posterior aspect of the muscle being covered only by transversalis fascia and peritoneum. Synonym: lamina posterior vaginae musculi recti abdominis. (05 Mar 2000) |
| cruciform part of fibrous digital sheath | The fibres of the fibrous sheath of the fingers and toes which form X-shaped patterns over the region of the interphalangeal joints. Synonym: pars cruciformis vaginae fibrosae, crucial ligament, cruciform part of fibrous sheath, cruciform pulley, ligamenta cruciata digitorum. (05 Mar 2000) |
| cruciform part of fibrous sheath | The fibres of the fibrous sheath of the fingers and toes which form X-shaped patterns over the region of the interphalangeal joints. Synonym: pars cruciformis vaginae fibrosae, crucial ligament, cruciform part of fibrous sheath, cruciform pulley, ligamenta cruciata digitorum. (05 Mar 2000) |
| crural sheath | The fascia enclosing the femoral vessels, formed by the transversalis fascia anteriorly and the iliac fascia posteriorly; two septa divide the sheath into three compartments, the lateral of which contains the femoral artery and the femoral branch of the genitofemoral nerve, the middle the femoral vein, and the medial is the femoral canal. Synonym: crural sheath, infundibuliform sheath. (05 Mar 2000) |