Muscle Fibers
| Medical Definition: |
Large, multinucleate single cells, either cylindrical or prismatic in shape, that form the basic unit of skeletal muscle tissue. They consist of a soft contractile substance enclosed in a tubular sheath. They are derived from the fusion of skeletal myoblasts (MYOBLASTS, SKELETAL) into a syncytium, followed by differentiation. |
| Guide Notes: |
MUSCLE FIBERS, FAST-TWITCH & MUSCLE FIBERS, SLOW-TWITCH are also available |
| Previously Indexed: |
Muscles (1966-1994) |
Muscle Fibers Categories.
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Muscle Fibers, Fast-Twitch - Skeletal muscle fibers 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 fibers, also called white fibers, 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 fibers, also called red fibers, have a large mitochondrial content and a high myoglobin content, related to their resistance to fatigue. (From Best, Physiological Basis of Medical Practice, 12th ed, p100) |
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Muscle Fibers, Slow-Twitch - Skeletal muscle fibers 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. (From Best, Physiological Basis of Medical Practice, 12th ed, p101) |
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Myofibrils - Highly organized bundles of actin (=ACTINS), MYOSINS, and other proteins in the cytoplasm of skeletal and cardiac muscle cells that contract by a sliding filament mechanism. |
Muscle Fibers Medical Definitions and Terms
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