• question_answer
                The functional unit of contractile system in striated muscle is:                                                        

    A)              cross bridge

    B)              myofibril

    C)              sarcomere   

    D)              Z-band

    Correct Answer: C

    Solution :

                A skeletal muscle consists of a bundle of long fibers running the length of the muscle. Each fiber is a single cell with many nuclei. Skeletal muscle is also called striated muscle because the regular arrangement of the myofilaments creates as repeating pattern of light and dark bands. Each repeating unit is a sarcomere, the basic functional unit of the muscle. The borders of the sarcomere, the Z lines, are lined up in adjacent myofibrils and contribute to the striations visible with a light microscope. The thin filaments are attached to the Z lines and project toward the center of the sarcomere while the thick filaments are centered in the sarcomere. At rest the thick and thin filaments do not overlap completely, and the area near the edge of the sarcomere where there are only thin filaments is called the I band. The A band is the broad region that corresponds to the length of the thick filaments. The thin filaments do not extend completely across the sarcomere, so the H zone in the center of the A band contains only thick filaments. This arrangement of thick and thin filaments is the key to how the sarcomere and hence the whole muscle contracts

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