Release of Calcium Ions

Correct Answer: D. Sarcoplasmic reticulum

Calcium ions are essential for muscle contraction to occur. Without the release of calcium, the myosin head would be unable to bind to the actin at the binding sites. It is the calcium that binds and removes troponin from the myosin binding sites on the actin. This is done when the axon terminal nearest a muscle fiber releases acetylcholine, a neurotransmitter, which then causes the sarcoplasmic reticulum to release calcium into the muscle cell to allow for muscle contraction. The endoplasmic reticulum is responsible for protein modification following translation on a ribosome.

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