n. one of the basic contractile units of which *striated muscle fibres are composed.
a tissue comprising the bulk of the body’s musculature. It is also known as skeletal muscle, because it is attached to the skeleton and is responsible for the movement of bones, and voluntary muscle, because it is under voluntary control. Striated muscle is composed of parallel bundles of multinucleate fibres (each containing many myofibrils), which reveal cross-banding when viewed under the microscope. This effect is caused by the alternation of actin and myosin protein filaments within each myofibril (see illustration). According to the ‘sliding filament’ theory, when muscle contraction takes place, the two sets of filaments slide past each other, so reducing the length of each unit (sarcomere) of the myofibril. The sliding is caused by a series of cyclic reactions, requiring ATP, resulting in a change in orientation of projections on the myosin filaments; each projection is first attached to an actin filament but contracts and releases it to become reattached at a different site.... striated muscle
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