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step 2: The power stroke. ADP & P are released and myosin head pivots/ bends changing to its bent low energy state which allows actin filament pulling towards M line.

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Step 3: After ATP attaches to myosin the line between myosin and actin weakens & myosin head detaches.

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Step 4: ATP hydrolyzed to ADP & Pi the myosin head returns to prestroke high energy or cocked position.

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step 1: Energized myosin head attaches to actin myofilament forming cross bridge head.

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Step 3 and 4: Ca2+ combines w/ troponin and removes the blocking action of tropomyosin by changing the shape of actin so that the myosin binding sites are exposed. Myosin binds to actin forms cross bridge and contraction be

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Step 2: Transmission of action potential along T tubules cause the adjacent sarcoplasmic reticulum (SR) to release Ca2+ which flows into cytosol.

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Step 1:  The action potential moves down the sarcolemma and down the T tubules.

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The action potential causes calcium channels to open and allow calcium ions to enter neuron. Increase in calcium releases ACh into the cleft. ACh leads to activation of voltage gated sodium channels that pumps Na+ in and K+ out. More sodium is pumped in that K+ is pumped out causing depolarization. The depolarization initiates the action potential that moves down the sarcolemma. The K+ voltage gated channels open and K+ diffuses out of sarcolemma which is repolarization.