Muscle Contraction and Relaxation Summary

On relaxation: • the nerve impulse stops • Ca2+ ions are taken up by sarcoplasmic reticulum • myosin cross-bridges are ‘broken’ down and actin returns to the resting state • the muscle relaxes.

Muscle Contraction and Relaxation Summary

In resting muscle: • there are few or no electrical impulses reaching muscle • there are Ca2+ ions within sarcoplasmic reticulum • ATP is stored, not broken down

During a contraction: • nerve impulses travel along axons to the axon end plate • acetylcholine travels across the synaptic cleft to myofi bril • sarcoplasmic reticulum releases Ca2+ • myosin cross-bridges attach to actin • ATP is broken down and energy is released, causing cross-bridges to shorten • actin is pulled and slides over myosin and the muscle shortens or contracts.

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