| HC | hair cell; hairy cell; handicapped; head circumference; head compression; health care; healthy contr... |
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| HEC | hamster embryo cell; Health Education Council; human endothelial cell; hydroxyergocalciferol; hydrox... |
| HTC | hepatoma cell; hepatoma tissue culture; homozygous typing cell |
| HTLV-MA | cell membrane antigen associated with the human T-cell leukemia virus |
| ISC | immunoglobulin-secreting cells; insoluble collagen; International Society of Cardiology; Internation... |
| muscle | <anatomy> Tissue specialised for contraction. See twitch muscle, catch muscle: Cardiac muscle (heart muscle) is a striated but involuntary muscle responsible for the pumping activity of the vertebrate heart. The individual muscle cells are joined through a junctional complex known as the intercalated disc and are not fused together into multinucleate structures as they are in skeletal muscle. Skeletal muscle is a rather non-specific term usually applied to the striated muscle of vertebrates that is under voluntary control. The muscle fibres are syncytial and contain myofibrils, tandem arrays of sarcomeres. Smooth muscle is muscle tissue in vertebrates made up from long tapering cells that may be anything from 20-500m long. Smooth muscle is generally involuntary and differs from striated muscle in the much higher actin/myosin ratio, the absence of conspicuous sarcomeres and the ability to contract to a much smaller fraction of its resting length. Smooth muscle cells are found particularly in blood vessel walls, surrounding the intestine (especially the gizzard in birds) and in the uterus. The contractile system and its control resemble those of motile tissue cells (for example fibroblasts, leucocytes) and antibodies against smooth muscle myosin will cross react with myosin from tissue cells, whereas antibodies against skeletal muscle myosin will not. See: dense bodies. (18 Nov 1997) |
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| muscle, adductor | Any muscle that pulls inward toward the midline of the body. For example, the adductor muscles of the leg serve to pull the legs together. The opposite of adductor is abductor. To keep these similar sounding terms straight, medical students learn to speak of a b ductors versus a d ductors. (12 Dec 1998) |
| muscle biopsy | <investigation, procedure, surgery> A procedure which involves the removal of a small specimen of muscle tissue for microscopic analysis. A muscle biopsy is used to distinguish between neurological and myopathic (muscle disease) disorders, identify muscular dystrophy, diagnose muscle infections and identify connective tissue disorders (necrotising vasculitis). (21 Mar 1998) |
| muscle-bound | Denoting a condition in which individual muscles are overdeveloped but dyssynergic in concerted action. (05 Mar 2000) |
| muscle bundle | A group of muscle fibres ensheathed by connective tissue (perimysium). (05 Mar 2000) |
| muscle, central core disease of | One of the conditions that produces 'floppy baby' syndrome. Ccd causes hypotonia (inadequately toned muscles characterised by floppiness) in the newborn baby, slowly progressive muscle weakness, and muscle cramps after exercise. Muscle biopsy shows a key diagnostic finding (absent mitochondria in the centre of many type i muscle fibres). Ccd is inherited as a dominant trait. The ccd gene is on chromosome 19 (and involves ryanodine receptor-1). (12 Dec 1998) |
| muscle contraction | A process leading to shortening and/or development of tension in muscle tissue. Muscle contraction occurs by a sliding filament mechanism whereby actin filaments slide inward among the myosin filaments. (12 Dec 1998) |
| muscle curve | <investigation, physiology> A test which measures muscle response to nerve stimulation. Used to evaluate muscle weakness and to determine if the weakness is related to the muscles themselves or a problem with the nerves that supply the muscles. Abnormal results may be seen in myasthenia gravis, polymyositis, carpal tunnel syndrome, amyotrophic lateral sclerosis, alcoholic neuropathy, cervical spondylosis, dermatomyositis, familial periodic paralysis, Guillain-Barre syndrome, Lambert-Eaton syndrome, Friedreich's ataxia, mononeuritis multiplex, peripheral neuropathy, sciatic nerve disease and a variety of peripheral nerve disorders. (27 Sep 1997) |
| muscle denervation | The resection or removal of the innervation of a muscle or muscle tissue. (12 Dec 1998) |
| muscle epithelium | Spindle-shaped, contractile, smooth muscle-like cells of epithelial origin that are arranged longitudinally or obliquely around sweat glands and the secretory alveoli of the mammary gland; stellate myoepithelial cells occur around lacrimal and some salivary gland secretory units. Synonym: muscle epithelium. Origin: myo-+ epithelium (05 Mar 2000) |
| muscle fascicle | A bundle of muscle fibres surrounded by perimysium. (05 Mar 2000) |
| muscle fatigue | <physiology> A condition resulting from prolonged and strong contraction of a muscle. Studies during prolonged submaximal exercise have shown that muscle fatigue increases in a near direct proportion to the rate of muscle glycogen depletion. Muscle fatigue in short-term maximal exercise is associated with oxygen deprivation and an increased level of blood and muscle lactic acid, and an accompanying increase in hydrogen-ion concentration in the exercised muscle. (12 Dec 1998) |
| muscle fibre | <pathology> Component of a skeletal muscle comprising a single syncytial cell that contains myofibrils. Any of the cells of skeletal or cardiac muscle tissue. Skeletal muscle fibres are cylindrical multinucleate cells containing contracting myofibrils, across which run transverse striations, enclosed in a sarcolemma. Cardiac muscle fibres contain one or sometimes two nuclei and myofibrils and are separated from one another by an intercalated disk; although striated, cardiac fibres branch to form an interlacing network. 2. fast-twitch muscles. Skeletal muscle fibres having high myofibrillar atpase activity, high glycolytic enzyme activities, and an intermediate glycogen content which produce a fast twitch. There are two types. Fast fatigable fibres, also called white fibres, have a low myoglobin content, and a small mitochondrial content, and fatigue rapidly due to their limited glycogen content and low capacity for oxidative metabolism. Fast fatigue-resistant fibres, also called red fibres, have a large mitochondrial content and a high myoglobin content, related to their resistance to fatigue. 3. slow-twitch muscles. Skeletal muscle fibres having low myofibrillar atpase activity, low glycogen content, and high myoglobin content, high mitochondrial oxidative enzyme activities, and an intermediate mitochondrial content which produce a slow twitch and are fatigue-resistant. (12 Dec 1998) |
| muscle haemoglobin | <physiology> Protein (17.5 kD) found in red skeletal muscle. It was the first protein for which the tertiary structure was determined by X-ray diffraction, by J.C.Kendrew's group working on sperm whale myoglobin. It is a single polypeptide chain of 153 amino acids, containing a haem group bonded via its ferric iron to two histidine residues. It binds oxygen noncooperatively and has a higher affinity for oxygen than haemoglobin at all partial pressures. In capillaries oxygen is effectively removed from haemoglobin and diffuses into muscle fibres where it binds to myoglobin which acts as an oxygen store. (18 Nov 1997) |
| muscle hypertonia | <neurology, physiology> Abnormal increase in muscle tone. (12 Dec 1998) |