Glossary of Medical Terms

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MUSCLE FIBRE

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 other by an intercalated disk; although striated, cardiac fibres branch to form an interlacing network. 2. fast-twitch muscles. Skeletal muscle fibres having tall myofibrillar atpase activity, tall glycolytic enzyme activities, and an intermediate glycogen content which manufacture a quick twitch. There are two types. Quick fatigable fibres, also called white fibres, have a low myoglobin content, and a little mitochondrial content, and fatigue rapidly due to their limited glycogen content and low ability for oxidative metabolism. Quick fatigue-resistant fibres, also called red fibres, have a big mitochondrial content and a tall myoglobin content, related to their resistance to fatigue. 3. slow-twitch muscles. Skeletal muscle fibres having low myofibrillar atpase activity, low glycogen content, and tall myoglobin content, tall mitochondrial oxidative enzyme activities, and an intermediate mitochondrial content which manufacture a slow twitch and are fatigue-resistant.
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