| membrane depolarisation | The process or act of neutralising polarity, depriving of polarity, or the result of such action; reduction to an unpolarised condition. <physiology> The reversal of the resting potential in excitable cell membranes when stimulated i.e., the tendency of the cell membrane potential to become positive with respect to the potential outside the cell. A positive shift in a cells resting potential (that is normally negative), thus making it numerically smaller and less polarized, for example 90mV to 50mV. <optics> Depolarisation of light, a change in the plane of polarization of rays, especially by a crystalline medium, such that the light which had been extinguished by the analyser reappears as if the polarization had been anulled. The word is inappropriate, as the ray does not return to the unpolarised condition. Origin: Cf. F. Depolarisation. (27 Oct 1998) |
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| dendritic depolarisation | The loss of a negative charge in the dendrites of a nerve cell. (05 Mar 2000) |
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| depolarisation | The process or act of neutralising polarity, depriving of polarity, or the result of such action; reduction to an unpolarised condition. <physiology> The reversal of the resting potential in excitable cell membranes when stimulated i.e., the tendency of the cell membrane potential to become positive with respect to the potential outside the cell. A positive shift in a cells resting potential (that is normally negative), thus making it numerically smaller and less polarized, for example 90mV to 50mV. <optics> Depolarisation of light, a change in the plane of polarization of rays, especially by a crystalline medium, such that the light which had been extinguished by the analyser reappears as if the polarization had been anulled. The word is inappropriate, as the ray does not return to the unpolarised condition. Origin: Cf. F. Depolarisation. (27 Oct 1998) |
| adamantine membrane | The primary enamel cuticle, consisting of two extremely thin layers (the inner one clear and structureless, the outer one cellular), covering the entire crown of newly erupted teeth and subsequently abraded by mastication; it is evident microscopically as an amorphous material between the attachment epithelium and the tooth. Synonym: cuticula dentis, adamantine membrane, dental cuticle, membrana adamantina, Nasmyth's cuticle, Nasmyth's membrane, skin of teeth. (05 Mar 2000) |
| allantoid membrane | An embryonic diverticulum of the hindgut of reptiles, birds, and mammals; in man its blood vessels give rise to those of the umbilical cord. (12 Dec 1998) |
| alveolocapillary membrane | The pulmonary diffusion barrier. (05 Mar 2000) |
| alveolodental membrane | <anatomy> Fibrous connective tissue surrounding the root of a tooth that separates it from and attaches it to the alveolar bone. (12 Dec 1998) |
| anal membrane | The dorsal portion of the embryonic cloacal membrane after its division by the urorectal septum. Anterior atlanto-occipital membrane, the fibrous layer that extends from the anterior arch of the atlas to the anterior margin of the foramen magnum. Synonym: membrana atlanto-occipitalis anterior. (05 Mar 2000) |
| anisotropic membrane | This type of synthetic membrane has an asymmetric pore structure: a thinfilm with tight pores backed by a thicker film with wider pores. Thistype of membrane is used for ultrafiltration andreverse osmosis, the porous side faces the feed stream and the tight-pored side faces the product stream. (09 Oct 1997) |
| anterior recess of tympanic membrane | A slitlike space on the tympanic wall between the anterior malleolar fold and the tympanic membrane. Synonym: recessus membranae tympani anterior, Troltsch's pockets, Troltsch's recesses. (05 Mar 2000) |
| anti-basement membrane antibody | Autoantibodies to renal glomerular basement membrane antigens. (05 Mar 2000) |
| anti-basement membrane glomerulonephritis | Glomerulonephritis resulting from anti-basement membrane antibodies, characterised by smooth linear deposits of IgG and C3 along glomerular capillary walls; includes rapidly progressive glomerulonephritis and glomerulonephritis in Goodpasture's syndrome. (05 Mar 2000) |
| anti-basement membrane nephritis | Glomerulonephritis produced by autologous or heterologous antibodies to the glomerular capillary basement membranes, the latter known as anti-kidney serum nephritis. (05 Mar 2000) |
| anti-glomerular basement membrane disease | Glomerulonephritis, usually of a generalised proliferative crescent-forming histologic type with a rapidly progressive course, marked by circulating anti-gbm antibodies and linear deposits of immunoglobulin and complement along the glomerular basement membrane. When associated with pulmonary haemorrhage the condition is called goodpasture syndrome. (12 Dec 1998) |
| apical plasma membrane | <cell biology> The term used for the cell membrane on the apical (inner or upper) surface of transporting epithelial cells. This region of the cell membrane is separated, in vertebrates, from the baso lateral membrane by a ring of tight junctions that prevents free mixing of membrane proteins from these two domains. (18 Nov 1997) |
| arachnoid membrane | Like a cobweb, covered with or consisting of soft fibres or hairs so entangled as to give a cobwebby appearance. (09 Oct 1997) |