| major groove | In a detailed analysis of DNA structure, there are two types of grooves that can be seen; the major groove has the nitrogen and oxygen atoms of the base pairs pointing inward toward the helical axis, while in the minor groove, the nitrogen and oxygen atoms point outwards; important because the major groove is more dependent on base composition and may be the site for protein recognition of specific DNA sequences or regions. (05 Mar 2000) |
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| major hippocampus | <anatomy> Area of mammallian brain and an important preparation for the study of synaptic plasticity. The hippocampus has been known since the 1950s to be important for long term memory storage in humans and other mammals, it is essential for initial storing of long-term memory for a period of days to weeks before the memory trace is consolidated elsewhere. Also the site of long-term synaptic plasticity: see long-term potentiation, which is exhibited by defined synaptic pathways in the hippocampus. (18 Nov 1997) |
| major histocompatabilty complex | <immunology> A cluster of genes on chromosome 6 concerned with antigen production and critical to transplantation. The MHC includes the human leukocyte antigen (HLA) genes. (12 Dec 1998) |
| major histocompatibility antigen | <immunology> A set of plasmalemmal glycoprotein antigens involved in rapid (e.g. 7 days in the mouse) graft rejection and other immune phenomena. The minor histocompatibility antigens are involved in much slower rejection phenomena. The major antigens show remarkable polymorphism and occur as Class I and Class II types in mammals, birds may have a Class III molecule as well. See: histocompatibility antigens, MHC restriction. (18 Nov 1997) |
| major histocompatibility complex | The set of gene loci specifying major histocompatibility antigens, for example HLA in man, H 2 in mice, RLA in rabbits, RT 1 in rats, DLA in dogs, SLA in pigs, etc. Acronym: MHC (18 Nov 1997) |
| major hypnosis | A state of extreme suggestibility in hypnosis in which the subject is insensible to all outside impressions except the commands of the hypnotist. (05 Mar 2000) |
| major hysteria | A syndrome, now rarely seen, described by Charcot and characterised by a first stage of aura, a second stage of epileptoid convulsions, a third stage of tonic and clonic spasms, a fourth stage of dramatic behaviour, and a fifth stage of delirium; the entire attack may last from a few minutes to half an hour. Sometimes used as a synonym for hysteroepilepsy. (05 Mar 2000) |
| major intrinsic protein | <protein> Family of structurally related proteins with 6 transmembrane segments, associated with gap junctions or vacuoles. MIP is found in lens fibre gap junctions. Other members: nodulin 26 (soybean), tonoplast intrinsic protein (TIP) found in plant storage vacuoles, Drosophila neurogenic protein big brain. (18 Nov 1997) |
| major mood disorder | See: bipolar disorder, affective psychosis, endogenous depression, dysthymia. (05 Mar 2000) |
| major motor seizure | A grand mal seizure or other convulsive seizure. (05 Mar 2000) |
| major operation | An extensive, relatively difficult surgical procedure involving vital organs and/or in itself hazardous to life. (05 Mar 2000) |
| major salivary glands | A category of salivary gland's that includes the three largest gland's of the oral cavity that also secrete most of the saliva: the parotid, submandibular, and sublingual gland's. (05 Mar 2000) |
| major source | A source that emits, or has the potential to emit, a pollutant regulated under the Clean Air act in excess of a specified rate in a nonattainment area. (05 Dec 1998) |
| major sublingual duct | The duct that drains the anterior portion of the sublingual gland; it opens at the sublingual papilla. Synonym: ductus sublingualis major, Bartholin's duct. (05 Mar 2000) |
| major surgery | See: major operation. (05 Mar 2000) |