| 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) |
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| 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) |
| hair colour | Colour of hair or fur. (12 Dec 1998) |
| hair crosses | Crosslike figures formed by hairs growing from two directions that meet and then separate in a direction perpendicular to the original orientation. Synonym: hair crosses. (05 Mar 2000) |
| hair cycle | The cyclical phases of growth (anagen), regression (catagen), and quiescence (telogen) in the life of a hair. (05 Mar 2000) |
| hair diseases | Diseases affecting the orderly growth and persistence of hair. (12 Dec 1998) |
| hair disk | A richly innervated area of skin around a hair follicle, consisting of a thickened layer of epithelial cells in which ramify unmyelinated terminals of a single axon. (05 Mar 2000) |
| hair dyes | Dyes used as cosmetics to change hair colour either permanently or temporarily. (12 Dec 1998) |
| hair follicle | <dermatology> A tube-like opening in the epidermis where the hair shaft develops and into which the sebaceous glands open (13 Nov 1997) |
| hair grass | <botany> A grass with very slender leaves or branches; as the Agrostis scabra, and several species of Aira or Deschampsia. Source: Websters Dictionary (01 Mar 1998) |
| cuticle of hair | A layer of overlapping shingle-like cells that invest the hair cortex and serve to lock the hair shaft in its follicle. Synonym: cuticle of hair. Cuticula vaginae folliculi pili, cuticle of overlapping shingle-like cells lining the follicle of the hair. Synonym: cuticle of root sheath. (05 Mar 2000) |