| cochlear hair cell | <anatomy> The sound sensing cell of the inner ear. The cells have modified ciliary structures (hairs), that enable them to produce an electrical (neural) response to mechanical motion caused by the effect of sound waves on the cochlea. Frequency is detected by the position of the cell in the cochlea and amplitude by the magnitude of the disturbance. (18 Nov 1997) |
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| cochlear hair cells | Sensory cell's in the organ of Corti in synaptic contact with sensory as well as efferent fibres of the cochlear (auditory) nerve; from the apical end of each cell about 100 stereocilia extend from the surface and make contact with the tectorial membrane. Synonym: Corti's cells. (05 Mar 2000) |
| pigmented hair epidermal nevus | A nevus first seen as an irregular pigmentation of the shoulders, upper chest, or scapular area, gradually enlarging irregularly and becoming thickened and hairy. Synonym: pigmented hair epidermal nevus. (05 Mar 2000) |
| moniliform hair | An autosomal dominant trichodystrophy in which brittle hairs show a series of constrictions, usually without a medulla. Synonym: beaded hair, moniliform hair. Origin: L. Monile, necklace, + G. Thrix, hair (05 Mar 2000) |
| woolly hair | Tightly coiled hair, oval in cross-section, with the texture of wool. (05 Mar 2000) |
| woolly-hair nevus | A circumscribed patch of fine, curly hair in an otherwise normal scalp appearing during childhood and enlarging for a period of 2 to 3 years; autosomal dominant inheritance. There is another, mostly sporadic form that may be autosomal recessive. Synonym: allotrichia circumscripta. (05 Mar 2000) |
| hair | 1. The collection or mass of filaments growing from the skin of an animal, and forming a covering for a part of the head or for any part or the whole of the body. 2. One the above-mentioned filaments, consisting, in invertebrate animals, of a long, tubular part which is free and flexible, and a bulbous root imbedded in the skin. "Then read he me how Sampson lost his hairs." (Chaucer) "And draweth new delights with hoary hairs." (Spenser) 3. Hair (human or animal) used for various purposes; as, hair for stuffing cushions. 4. <zoology> A slender outgrowth from the chitinous cuticle of insects, spiders, crustaceans, and other invertebrates. Such hairs are totally unlike those of vertebrates in structure, composition, and mode of growth. 5. An outgrowth of the epidermis, consisting of one or of several cells, whether pointed, hooked, knobbed, or stellated. Internal hairs occur in the flower stalk of the yellow frog lily (Nuphar). 6. A spring device used in a hair-trigger firearm. 7. A haircloth. 8. Any very small distance, or degree; a hairbreadth. Hairs is often used adjectively or in combination; as, hairbrush or hair brush, hair dye, hair oil, hairpin, hair powder, a brush, a dye, etc, for the hair. Against the hair, in a rough and disagreeable manner; against the grain. "You go against the hair of your professions." . <anatomy> Hair bracket, the thinnest metal space used in lines of type. Hair stroke, a delicate stroke in writing. Hair trigger, a trigger so constructed as to discharge a firearm by a very slight pressure, as by the touch of a hair. Not worth a hair, of no value. To a hair, with the nicest distinction. To split hairs, to make distinctions of useless nicety. Origin: OE. Her, heer, haer, AS. Haer; akin to OFries, her, D. & G. Haar, OHG. & Icel. Har, Dan. Haar, Sw. Har; cf. Lith. Kasa. Source: Websters Dictionary (01 Mar 1998) |
| hair ball | A hair cast in the stomach or intestinal tract, common in cats. Synonym: hair ball, pilobezoar. Origin: tricho-+ bezoar (05 Mar 2000) |
| hair bulb | Hair bulb, the lower expanded extremity of the hair follicle that fits like a cap over the papilla pili. Synonym: bulbus pili, hair bulb. (05 Mar 2000) |
| hair cast | 1. A cast composed of parakeratotic scales attached to scalp hair but freely movable up and down the hair shaft; found in scaling dermatitis of the scalp, including dandruff, psoriasis, and seborrheic dermatitis. Synonym: pseudonit. 2. A small, nodular accretion of epithelial cells and keratinous debris resulting from failure of the internal root sheath to disintegrate; it appears for 3 to 7 mm along the hair shaft. (05 Mar 2000) |
| hair cell | 1. <biology> Cells found in the epithelial lining of the labyrinth of the inner ear. The hairs are stereovilli up to 25 m long that restrict the plane in which deformation of the apical membrane of the cell can be brought about by movement of fluid or by sound. Movement of the single stereocilium transduces mechanical movements into electrical receptor potentials. 2. <plant biology> Many plant surfaces are covered with fine hairs (Tradescantia stamens are a common source), the hairs are made up of thin walled cells that are convenient for studying cytoplasmic streaming and for observing mitosis. (13 Nov 1997) |
| hair cells | Mechanoreceptors located in the organ of corti that are sensitive to auditory stimuli and in the vestibular apparatus that are sensitive to movement of the head. In each case the accessory sensory structures are arranged so that appropriate stimuli cause movement of the hair-like projections (stereocilia and kinocilia) which relay the information centrally in the nervous system. (12 Dec 1998) |
| hair cells, inner | Bulbous cells that are medially placed in one row in the organ of corti. In contrast to the outer hair cells, the inner hair cells are fewer in number, have fewer sensory hairs, and are less differentiated. (12 Dec 1998) |
| hair cells, outer | Mechanoreceptors in the organ of corti. In mammals the outer hair cells are arranged in three rows which are further from the modiolus than the single row of inner hair cells. The motile properties of the outer hair cells may contribute actively to tuning the sensitivity and frequency selectivity of the cochlea. (12 Dec 1998) |
| hair cells, vestibular | Mechanoreceptors located in the acoustic maculae and the saemicircular canals that mediate the sense of balance, movement, and head position. The vestibular hair cells are connected to accessory structures in such a way that movements of the head displace their stereocilia. This influences the membrane potential of the cells which relay information about movements via the vestibular part of the acoustic nerve to the brainstem. (12 Dec 1998) |