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Step 4: As ATP is hydrolyzed to ADP and pi, the myosin head returns to its prestroke high energy.

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Step 3: ATP attaches myosin the line between myosin and actin weaken and the myosin head attaches.

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step 2: ADP and pi are released and the myosin head pivots and bends changing to bent low energy. As a result it pulls the actin filament to the M line.

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step 1: cross bridge formation: energized myosin head attaches to an actin myofilament forming a cross bridge.

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Step 3: Ca+2 combines with troponin and removes the blocking action of the tropomyosin by changing shape of the actin so the myosin binding sites are exposed.

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Step 2: Transmission of the action potential along the T tubes cause the adjacent sarcoplasmic reticulum and release Ca+2 then flows into cytosol.

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Step 1:
Action potential moves down the sarcolemma and down T tubes.

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Step 1: The brain sends a nerve impulse (action potential) through the motor unit to the neuromuscular junction.
Step 2: The action potential causes voltage gated calcium ion channels to open and calcium ions enter. Acetylcholine is stimulated and is released into the cleft.
Step 3: ACh binds to a Ach receptor and activates voltage gated sodium channels. Na+ is pumped into the cell and K+ is pumped out. The cell interior is then depolarized.
Step 4: Depolarization spreads and opens voltage gated sodium channels and causes and action potential that moves along the sarcolemma.
Step 5: Na+ concentrations that was caused by depolarization stimulate membrane change and open voltage gated K+ pumps and allow K+ to diffuse across the sarcolemma out of the muscle fiber and cause repolarization.