- 1. A thin sheet or layer of pliable tissue, serving as a covering or envelope of a part, as the lining of a cavity, as a partition or septum, or to connect two structures. SYN: membrana [TA]. 2. SYN: biomembrane. [L. membrana, a skin or m. that covers parts of the body, fr. membrum, a member]- anal m. the dorsal portion of the embryonic cloacal m. after its division by the urorectal septum.- anterior atlanto- occipital m. [TA] the fibrous layer that extends from the anterior arch of the atlas to the anterior margin of the foramen magnum of the occipital bone. SYN: membrana atlanto- occipitalis anterior [TA].- Barkan m. a theoretical tissue covering the trabecular meshwork; thought to obstruct aqueous humor outflow and be responsible for congenital glaucoma.- basal m. of semicircular duct the basal m. underlying the epithelium of the semicircular duct. SYN: basal lamina of semicircular duct, membrana basalis ductus semicircularis.- basement m. an amorphous extracellular layer closely applied to the basal surface of epithelium and also investing muscle cells, fat cells, and Schwann cells; thought to be a selective filter and to serve both structural and morphogenetic functions. It is composed of three successive layers (lamina lucida, lamina densa, and lamina fibroreticularis), a matrix of collagen (of which type IV is unique to this m.), and several glycoproteins. SYN: basement lamina, basilemma.- bucconasal m. a thin, transient epithelial sheet separating the primitive nasal cavity from the stomodeum in the 7-week-old human embryo. SYN: oronasal m..- buccopharyngeal m. a bilaminar (ectoderm and endoderm) m. derived from the prochordal plate; after the embryonic head fold has evolved it lies at the caudal limit of the stomodeum. SYN: oral m., oropharyngeal m..- cell m. the protoplasmic boundary of all cells that controls permeability and may serve other functions through surface specializations; e.g., active ion transport absorption by formation of pinocytotic vesicles; receptor-mediated antigen recognition, etc.; its fine structure is trilaminar and consists of the electron-dense lamina externa and lamina interna with an electron-lucent lamina intermedia. SYN: cytolemma, cytomembrane, plasma m., plasmalemma, plasmolemma, Wachendorf m. (2).- cloacal m. a transitory m. in the caudal area of the embryo, separating the proctodeum from the cloaca; it is divided into anal and genitourinary membranes that break down during the 8th to 9th week of human development to establish the external opening for the alimentary and genitourinary tracts.- closing membranes thin sheets, composed of ectoderm externally and endoderm internally, which separate the pharyngeal pouches from the overlying branchial clefts in the early embryo. SYN: pharyngeal membranes.- cricothyroid m. one of the bilateral membranes extending between the arch of the cricoid cartilage and the inferior edge of the thyroid lamina on each side of the midline, which is occupied by the thicker median cricothyroid ligament. SEE ALSO: conus elasticus, median cricothyroid ligament. SYN: membrana cricothyroidea.- cricotracheal m. SYN: cricotracheal ligament.- cricovocal m. conus elasticus.- croupous m. SYN: false m..- deciduous m. the mucous m. of the pregnant uterus that has already undergone certain changes, under the influence of the ovulation cycle, to fit it for the implantation and nutrition of the ovum; so called because the m. is cast off after labor. SYN: caduca, decidua, Hunter m., membrana decidua.- double m. two biomembrane layers, with an intermembranal space, surrounding certain organelles ( E.G., mitochondria) or structures.- drum m. SYN: tympanic m..- egg m. the investing envelope of the ovum; a primary egg m. is produced from ovarian cytoplasm ( e.g., a vitelline m.); a secondary egg m. is the product of the ovarian follicle ( e.g., the zona pellucida); a tertiary egg m. is secreted by the lining of the oviduct ( e.g., a shell).- elastic m. a m. formed of elastic connective tissue, present as fenestrated lamellae in the coats of the arteries and elsewhere.- epipapillary m. 1. a congenital m. covering the optic disk; 2. the glial remnants of Bergmeister papilla.- epiretinal m. a m., usually acquired, covering a portion of the retina and composed of fibrous tissue from metaplasia of retinal pigment epithelial cells or glia.- exocelomic m. a layer of cells delaminated from the inner surface of the blastocystic cytotrophoblast and from the envelope of the primary yolk sac during the second week of embryonic life. SYN: Heuser m..- external intercostal m. [TA] the m. that replaces the external intercostal muscle anteriorly, between costal cartilages. SYN: membrana intercostalis externa [TA].- false m. a thick, tough fibrinous exudate or slough on the surface of a mucous m. or the skin, as seen in diphtheria. SYN: croupous m., pseudomembrane.- fertilization m. a viscous m. formed on the inner surface of the vitelline m. from the cytoplasm of the egg cell after entry of the sperm, preventing the entry of additional sperm.- fetal m. a structure or tissue that develops from the fertilized ovum but does not form part of the embryo proper. SYN: embryonic m., extraembryonic m..- fibroelastic m. of larynx [TA] a layer of fibrous and elastic fibers, taking the place of the submucosa in the larynx. It is divided by the laryngeal ventricle into two parts: the quadrangular m. superiorly and the conus elasticus inferiorly. SYN: membrana fibroelastica laryngis [TA].- glassy m. 1. the basement m. present between the stratum granulosum and the theca interna of a vesicular ovarian follicle; it becomes very prominent in large atretic follicles; 2. the basement m. and associated connective tissue of the hair follicle. SYN: hyaline m. (2).- glial limiting m. a dense, resilient m. forming the true capsule of the brain and spinal cord, composed of the processes of astrocytes (macroglia cells) and covered throughout by the pia mater, which firmly adheres to it; the two membranes are collectively called the pial-glial m.. SYN: membrana limitans gliae.- Heuser m. SYN: exocelomic m..- hyoglossal m. posterior widening of the lingual septum connecting the root of the tongue to the hyoid bone; the inferior fibers of the genioglossus are attached to it and by this means to the upper anterior body of the hyoid bone near the midline.- inner m. the smaller of a double m..- intercostal membranes [TA] the membranous portion of the intercostal muscle layers between ribs. SYN: membranae intercostales [TA], intercostal ligaments, ligamenta intercostalia.- internal intercostal m. [TA] the m. that replaces the internal intercostal muscle posteriorly, medial to the angles of the ribs. SYN: membrana intercostalis interna [TA].- interosseous m. of forearm [TA] the dense m. that connects the interosseous margins of the radius and ulna, forming the radioulnar syndesmosis, and with those bones separating the flexor and extensor compartments of the forearm. SYN: membrana interossea antebrachii [TA].- interosseous m. of leg [TA] the dense fibrous layer that connects the interosseous margins of the tibia and fibula, forming the upper portion of the tibiofibular syndesmosis and, with the bones and intermuscular septa, creating anterior and posterior comparments of the leg. SYN: membrana interossea cruris [TA], ligamentum tibiofibulare medium.- ivory m. SYN: membrana eboris.- Jackson m. a thin vascular m. or veillike adhesion, covering the anterior surface of the ascending colon from the cecum to the right flexure; it may cause obstruction by kinking of the bowel. SYN: Jackson veil.- limiting m. of retina one of two layers of the retina : internal limiting m., formed by the expanded inner ends of Müller fibers; outer limiting m., not a m. but a row of junctional complexes. SYN: membrana limitans (1).- nictitating m. SYN: plica semilunaris of conjunctiva (2).- Nitabuch m. a layer of fibrin between the boundary zone of compact endometrium and the cytotrophoblastic shell in the placenta. SYN: Nitabuch layer, Nitabuch stria.- obturator m. [TA] the thin m. of strong interlacing fibers filling the obturator foramen and with the surrounding bone, giving origin to the obturator externus and internus muscles. SYN: membrana obturatoria [TA].- oronasal m. SYN: bucconasal m..- otolithic m. a gelatinous m. supported by the hairs of the hair cells of the maculae of the saccule and utriculus of the inner ear; adhering to the surface are numerous crystalline particles called otoliths (statoconia). SYN: membrana statoconiorum [TA], statoconial m..- outer m. the larger of the two membranes of a double m..- ovular m. SYN: membrana vitellina (1).- perineal m. [TA] the layer of fascia extending between the ischiopubic rami inferior to the sphincter urethrae and the deep transverse perineal muscles. SYN: membrana perinei [TA], Camper ligament, ligamentum triangulare, triangular ligament.- pharyngeal membranes SYN: closing membranes.- pial-glial m. the dual outer lining of the brain and spinal cord, composed of the glial limiting m. and the pia mater.- placental m. the semipermeable layer of fetal tissue separating the maternal from the fetal blood in the placenta; composed of: 1) endothelium of the fetal vessels in the chorionic villi, 2) stromata of the villi, 3) cytotrophoblast (negligible after the fifth month of gestation), and 4) syncytial trophoblast covering the villi; the placental m. acts as a selective m. regulating passage of substances from the maternal to the fetal blood. SYN: placental barrier.- posterior atlanto- occipital m. [TA] the fibrous m. that attaches between the posterior arch of the atlas and the posterior margin of the foramen magnum. SYN: membrana atlanto- occipitalis posterior [TA].- postsynaptic m. that part of the plasma m. of a neuron or muscle fiber with which an axon terminal forms a synaptic junction; in many instances, at least part of such a small postsynaptic m. patch shows characteristic morphological modifications such as greater thickness and higher electron density, believed to correspond to the transmitter-sensitive receptor site of such synapses.- presynaptic m. that part of the plasma m. of an axon terminal that faces the plasma m. of the neuron or muscle fiber with which the axon terminal establishes a synaptic junction; many synaptic junctions exhibit structural presynaptic characteristics, such as conical, electron-dense internal protrusions, that distinguish it from the remainder of the axon's plasma m.. SEE ALSO: synapse.- primary egg m. egg m..- proligerous m. SYN: cumulus oöphorus.- proper m. of semicircular duct [TA] the meshwork of connective tissue fibers between the semicircular duct and the bony semicircular canal; it forms a delicate meshwork within the otherwise perilymph-filled perilymphatic space. SYN: membrana propria ductus semicircularis, membrana propria of semicircular duct.- prophylactic m. SYN: pyogenic m..- pupillary m. remnants of the central portion of the anterior layer of the iris stroma (the iridopupillary lamina) which occludes the pupil in fetal life, and normally atrophies about the seventh month of gestation. Persistent strands usually stretch across the pupil from one iris collarette to the other, without touching the pupillary margin. Failure to regress is a rare cause of congenital blindness. SYN: membrana pupillaris, Wachendorf m. (1).- pyogenic m. a layer of pus cells lining an abscess cavity which have not yet autolyzed. SYN: prophylactic m..- quadrangular m. [TA] portion of the fibroelastic m. of the larynx that lies superior to the laryngeal ventricle; its slightly thickened inferior edge, the vestibular ligament, unlerlies the vestibular fold of the larynx; it attaches anteriorly to the epiglottis and posteriorly to the lateral margin of the arytenoid and corniculate cartilages; its upper portion underlies the mucosa of the aryepiglottic fold, which separates the laryngeal vestibule from the piriform fossa of the laryngopharynx. SYN: membrana quadrangularis [TA], Tourtual m..- reticular m. of spinal organ the m. formed by cuticular plates of the cells of the spiral organ of Corti; it appears netlike when viewed from above. SYN: membrana reticularis organi spiralis [TA].- schneiderian m. SYN: mucosa of nose.- secondary egg m. egg m..- secondary tympanic m. [TA] the m. closing the round window (fenestra cochleae). SYN: membrana tympani secundaria [TA], round window m., Scarpa m..- semipermeable m. a m. that is relatively permeable to the solvent but relatively impermeable to all or at least some of the solutes in either or both of the solutions separated by the m..- stapedial m. [TA] the delicate mucosal layer that bridges the space between the crura and base of the stapes. SYN: membrana stapedis [TA].- statoconial m. SYN: otolithic m..- sternal m. [TA] interlacing fibers from the anterior costosternal ligaments covering the anterior surface of the sternum. SYN: membrana sterni [TA].- striated m. SYN: zona striata.- suprapleural m. [TA] the thickened portion of endothoracic fascia extending over the cupola of the pleura and reinforcing it; it attaches to the inner border of the first rib and to the transverse process of the seventh cervical vertebra. SYN: membrana suprapleuralis [TA], Sibson aponeurosis, Sibson fascia.- synovial m. [TA] the connective tissue m. that lines the cavity of a synovial joint and produces the synovial fluid; it lines all internal surfaces of the cavity except for the articular cartilage of the bones. SYN: membrana synovialis [TA], stratum synoviale, synovium.- tectorial m. of cochlear duct [TA] a gelatinous m. that overlies the spiral organ (Corti) in the inner ear. SYN: membrana tectoria ductus cochlearis [TA], Corti m., tectorium (2).- tectorial m. (of median atlantoaxial joint) [TA] the upward continuation of the anterior part of the posterior longitudinal ligament attached to (spanning between) the upper surface of the basilar portion of the occipital bone and the bodies of the second and third cervical vertebrae; it forms a “roof” over the median atlantoaxial joint. SYN: membrana tectoria (articulationis atlantoaxialis medianae) [TA], apparatus ligamentosus weitbrechti, posterior occipitoaxial ligament.- tertiary egg m. egg m..- thyrohyoid m. [TA] a thin, fibrous, membranous sheet filling the gap between the hyoid bone and the thyroid cartilage. SYN: membrana thyrohyoidea [TA], membrana hyothyroidea.- tympanic m. [TA] a thin tense m. forming the greater part of the lateral wall of the tympanic cavity and separating it from the external acoustic meatus; it constitutes the boundary between the external and middle ear; it is a trilaminar m. covered with skin on its external surface, mucosa in its internal surface, is covered on both surfaces with epithelium, and, in the tense part, has an intermediate layer of outer radial and inner circular collagen fibers. SYN: membrana tympani [TA], drum m., drum, drumhead, m. of tympanum, myringa, myrinx.- undulating m., undulatory m. a locomotory organelle of certain flagellate (trypanosome and trichomonad) parasites, consisting of a finlike extension of the limiting m. with the flagellar sheath; wavelike rippling of the undulating m. produces a characteristic movement.- unit m. the trilaminar structure of the plasmalemma and other intercellular membranes, when seen in cross-section with the electron microscope, composed of two electron-dense laminae approximately 20 Å thick separated by a less dense lamina 35 Å thick.- urogenital m. the ventral portion of the embryonic cloacal m. after its division by the urorectal septum.- urorectal m. in the embryo, urorectal septum separating the cloaca into urogenital sinus and rectum. SYN: urorectal fold.- uteroepichorial m. rarely used term for decidua parietalis.- vitelline m. SYN: membrana vitellina (1).- vitreous m. 1. SYN: posterior limiting lamina of cornea. 2. a condensation of fine collagen fibers in places in the cortex of the vitreous body; formerly thought to form a m. or capsule at its periphery; 3. SYN: lamina basalis choroideae.- yolk m. SYN: membrana vitellina.
* * *mem·brane 'mem-.brān n1) a thin soft pliable sheet or layer esp. of animal or plant originmem·braned 'mem-.brānd adj
* * *n.1. a thin layer of tissue surrounding the whole or part of an organ or tissue lining a cavity, or separating adjacent structures or cavities. See also basement membrane, mucous membrane, serous membrane.• membranous adj.
* * *mem·brane (memґbrān) a thin layer of tissue that covers a surface, lines a cavity, or divides a space or organ; see also membrana. membranaceous, membranous adj
For names of specific anatomic structures not found here, see under membrana.
Medical dictionary. 2011.