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6 muscle 118 - Biology 118 6 MUSCLES AND MOVEMENT MUSCLE...

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Biology 118 6. MUSCLES AND MOVEMENT MUSCLE TYPES : there are three general kinds of muscle, Skeletal – connected to the skeleton by tendons, they are under voluntary control. Smooth – these involuntary muscles generally surround the hollow organs. Cardiac – the heart is a muscle, after all. OVERALL STRUCTURE : A skeletal muscle contains connective tissue, blood vessels and muscle cells. Muscle fibers (cells) can be very long, and are multinucleated (owing to the fusion of many embryonic muscle cells in development). They are arranged in parallel within the muscle. Myofibrils are specialized structures inside muscle fibers. They are made up of sarcomeres linked end-to-end. Sarcomeres are the functional unit of the muscle. They contain thick (myosin) and thin (actin) myofilaments that interdigitate and overlap. These myofilaments are attached the each end of the sarcomere, and can pull on each other to shorten the sarcomere. Each individual sarcomere can shorten, so: When sarcomeres in a myofibril shorten, the whole myofibril shortens. When myofibrils in a muscle fiber (muscle cell) shorten, the muscle itself shortens (contracts), pulling on either end and producing tension. SLIDING FILAMENT MODEL : Sarcomeres shorten when thick and thin filaments slide along each other: the Z-lines (at either end of the sarcomere) move closer together, thin filaments move closer to the center. Myosin heads bind to actin. ATP and Ca 2+ are required for sliding to occur.
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