Skeletal muscle. Light micrograph of a longitudinal section through leg skeletal muscle fibres. Muscle fibres are long, cylindrical cells (running left to right). Running the length of each fibre are thin threads called myofibrils (not seen). The cross striations (stripes) are due to the regular arrangement of contractile proteins in these myofibrils. These proteins (actin and myosin) slide past each other when a muscle contraction takes place, shortening the fibre. Stained blue is the collagen of connective tissue which controls the degree of muscle extension and contraction. Skeletal muscle is under voluntary control. Magnification x250 at 5x7cm size.
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