The contraction cycle in the muscles is a myosin-actin cycle that brings about the movement. The sarcoplasmic reticulum releases calcium ions to trigger the contraction. Thus, option C is correct.
Muscle contraction is the increase or shortening in the length of the muscles and tightness to do some muscular activity. It includes the nervous and muscular systems.
The calcium ions are released from the SR due to the depolarization of the muscle membrane and fibers, initiated by the nerve stimulation. The decrease in calcium levels relaxes the muscles.
Therefore, the calcium ions cause contraction.
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