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step 1: detailed description

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Step 4: detailed description

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step 2: detailed description

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Step 3: detailed description

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Step 3 and 4: Ca2+ combines with troponin and removes the blocking action tropomyosin by changing shape of the actin. The myosin sites become exposed. The myosin binds to actin and forms a cross bridge and the contraction begins.

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Step 2: The transmission of the action potential along the T tubules cause the adjacent sarcoplasmic reticulum to release Ca2+ that flows into cytosol.

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Step 1 : An action potential moves down the sarcolemma and down the T tubules. These protrude deep into the muscle cell

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Step 1 : The Brain sends a nerve impulse (Action potential) through the motor unit and down the neurotransmitter junction. Step 2 : Nerve impulse causes voltage gated Ca+ to enter in neuron. The increase of Ca+ stimulates the release of neurontranmitters acetylcholine which is then released into the cleft. Step 3 : Acetylcholine binds to the ACh receptor sight and activates voltage gated Na+ channel that pumps Na+ in and K+ out. Causes for the cell to become depolarized. Step 4 : Depolarization spreads, opening voltage gated Na+ channels and initiating an action potential that moves along the sarcolemma. Step 5 : Na+ concentration cause for voltage gated K+ channels to be opened and allows k+ to diffuse across the sarcolemma known as repolarization.