When a muscle is at rest, a protein called tropomyosin will be blocking the actin-myosin binding site., When an impulse arrives at the muscle, there is an influx of calcium ions into the myofilament from the sarcoplasmic reticulum., The calcium ions bind to troponin which causes tropomyosin to move out of the binding site, leaving the binding site exposed., The myosin globular head is able to bind to the binding site on the actin, forming an actin-myosin cross bridge., Hydrolysis of ATP on myosin head releases energy which causes the myosin head to pivot, which pulls the actin filament along (power stroke), A new ATP molecule binding to the head causes the cross bridge holding actin and myosin together to break., Myosin head attaches to the next binding site..




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