| nerve sheath tumours | Tumours arising in the sheath surrounding the axon of some nerve cells and formed by the plasma membrane of schwann cells in the peripheral nervous sytem and by oligodendrocytes in the central nervous system. Neurofibromas and neurilemmomas are the most commonly occurring tumours of this type. (12 Dec 1998) |
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| Neumann's sheath | A layer of tissue relatively resistant to the action of acids, which forms the walls of the dentinal tubules. Synonym: Neumann's sheath. (05 Mar 2000) |
| neurovascular sheath | Fibrous tissue enveloping and binding together arteries, their accompanying veins (venae comitantes) and nerves which run together; often it is merely the adventitious tissue of the neurovascular structures, but may be highly developed as a distinct fascial layer (e.g., in the case of the carotid or axillary sheaths). (05 Mar 2000) |
| notochordal sheath | The fibrous outer covering of the notochord. (05 Mar 2000) |
| Debye sheath | <radiobiology> The region of strong electric field in front of a material surface in contact with a plasma. Its characteristic thickness is the Debye length, and it is caused by Debye shielding of the negative surface charge resulting from electrons flowing to the surface much faster (initially) than the ions. The lost electrons leave behind a region of net positive charge which gradually diminishes the strength of the electric field over the Debye length. (13 Nov 1997) |
| dentinal sheath | A layer of tissue relatively resistant to the action of acids, which forms the walls of the dentinal tubules. Synonym: Neumann's sheath. (05 Mar 2000) |
| synovial sheath | See: synovial tendon sheath, vagina synovialis trochleae, synovial sheaths of digits of hand, synovial sheaths of digits of foot. (05 Mar 2000) |
| synovial tendon sheath | 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) |
| dural sheath | An extension of the dura mater that ensheathes the roots of spinal nerves or, more particularly, the vagina externa nervi optici. (05 Mar 2000) |
| dural sheath of optic nerve | <anatomy, nerve> The outer sheath around the optic nerve, continuous with the dura mater. Synonym: vagina externa nervi optici, dural sheath of optic nerve. (05 Mar 2000) |
| infundibuliform 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) |
| inner sheath | The material that encases the two central microtubules of the ciliary axoneme. (18 Nov 1997) |
| internal sheath of optic nerve | <anatomy, nerve> The innermost sheath around the optic nerve, continuous with the leptomeninges (pia-arachnoid) and including a cerebrospinal fluid-filled intervaginal space, continuous with the subarachnoid space. Synonym: vagina interna nervi optici. (05 Mar 2000) |
| intertubercular sheath | The extension of the synovial membrane of the shoulder joint downward in the intertubercular groove to surround the tendon of the long head of the biceps. Synonym: vagina intertubercularis. (05 Mar 2000) |
| optic nerve sheath decompression | A venting of the optic nerve sheath into the retrobulbar space, by slitting or by fenestrating the sheath. See: optic nerve sheath fenestration. (05 Mar 2000) |