| carotid sheath | The dense fibrous investment of the carotid artery, internal jugular vein, and vagus nerve on each side of the neck, deep to the sternocleidomastoid muscle; the layers of cervical fascia blend with it. Synonym: vagina carotica. (05 Mar 2000) |
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| rectus sheath | Sheath of the rectus abdominis, formed by the aponeuroses of the three anterolateral muscles of the abdominal wall that split to enclose the rectus and fuse medially to form the linea alba; it consists of an anterior lamina and a posterior lamina, the latter being absent below the arcuate line. See: aponeurosis of external abdominal oblique muscle, aponeurosis of internal abdominal oblique muscle. Synonym: vagina musculi recti abdominis. (05 Mar 2000) |
| parotid sheath | The part of the investing cervical fascia that ensheaths the parotid gland and is fixed above to the zygomatic arch. Synonym: fascia parotidea, fibrous capsule of parotid gland, parotid sheath. (05 Mar 2000) |
| Mauthner's sheath | <cell biology> Plasma membrane of an axon. (12 Mar 1998) |
| caudal sheath | A group of microtubules arranged cylindrically around the caudal pole of the nucleus in a developing spermatozoon. (05 Mar 2000) |
| resectoscope sheath | An operative sheath through which transurethral electroresection of bladder tumours or prostate gland can be performed. (05 Mar 2000) |
| 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) |
| 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) |
| 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) |