Which of the following is responsible for muscle relaxation?

A. The sarcomere runs out of ATP.

B. Calcium floods the area of the sarcomere, allowing for the interaction of actin and myosin.

C. Calcium is pumped back into the sarcoplasmic reticulum.

D. Acetylcholinesterase in the neuromuscular junction is depleted.

Option-C

Explanation:

The process of muscle contraction and relaxation is very complex and involves the electrical signals, calcium ions, ATP, proteins - actin, myosin, troponin, tropomyosin, and many others.

The process of muscle contraction begins when the neural signals lead to the release of the sarcoplasmic calcium ions and then calcium binds to troponin and allows the binding of the tropomyosin and formation of cross-bridge.

The muscle relaxes when the signals from the brain stop the release of the calcium ions from the sarcoplasmic reticulum and the released ions are pumped back in the reticulum.

Thus, Option-C is the correct answer.