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MUSCLES MOVE SKELETAL PARTS BY CONTRACTING Team 1 CONTRACTIONS The ability to move requires that the muscles be attached to the skeleton in antagonistic pairs When bicep contracts, triceps relax- When triceps contract, biceps relax THE STRUCTURE OF SKELETAL MUSCLE Muscle fiber consists of a bundle of long fibers running parallel to the length of the muscle Bundle of myofibrils arranged longitudinally MYOFIBRILS Two kinds of myofilaments : Thin filaments- two strands of actin and one strand of regulatory protein coiled around thick filament Thick filaments- staggered array of myosin CONTRACTIONS In a relaxed muscle fiber, the I bands and the H zone are relatively wide During contraction, the thick, and thin filaments slide past each other, reducing the width of the I bands and H zone and shortening the sacromere In a fully contracted muscle fiber, the thin filaments overlap, eliminating the H zone. The I bands disappear as the ends of the thick filaments contract the Z lines Myosin-Actin interactions underlying muscle fiber contraction See figure 49.30, page 1068 as we explain