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| What are the steps of Muscle Contraction? |
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Nerve impulses move to motor units. This is called innervation.
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When cell membrane of muscle cells/fibers of motor units are innervated there is a release of chemical from end of the nerve. The chemical is a neurotransmitter called acetylcholine(ACh). The ACh causes the process of muscle action potential.
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The muscle action potential causes calcium ions to be released from the storage sacs in the cell membrane and diffuse into the myofibrils.
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Calcium ions causes the opening of the binding sites on the actin filaments and myosin filaments form a cross bridge with the actin filament. Energy from the reaction ATP= ADP+ PO3 is needed to energize the ready.cock the myosin crossbridges. The myosin crossbridges bend outward and attach to the actin.
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Myosin crossbridges bend inward when ADP and PO3 released from myosin. This is known as the powerstroke.
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A "new" ATP binds on the myosin causing cross bridges to detach.
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| The process begins again and the crossbridges attach and detach 50 to 100 times sliding the z lines closer and closer together. Therefore the sarcomeres of the myofibrils of the muscle cells of the necessary motor units contract. This is muscle contraction. When innervation ceases, Calcium ions will return to storage sacs in the cell membranes of the muscle fibers and the z lines of the sarcomeres passively returned to their original positions. |
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