What terminates a muscle contraction?

Muscle contraction is terminated by a signal from the nervous system to the muscle to stop contracting. This signal causes the calcium ions that were responsible for activating the muscle to be pumped back into the sarcoplasmic reticulum, thereby lowering the concentration of calcium ions in the cytosol. The muscle also becomes refractory to further contraction during this relaxation phase, meaning that a new stimulation must be sent to the muscle in order to initiate another contraction.