4. An increase in calcium concentration in the sarcoplasm will cause which of the following? A. displacement of troponin tropomyosin complex from the actin binding sites
B. muscle relaxation
C. rapid repolarization of the muscle membrane
D. breaking of the actin/myosin cross-bridges
E. activation of calcium pumps in the sarcoplasmic reticulum

B. muscle relaxation

Explanation:

Sarcoplasmic reticulum store intracellular calcium in skeletal muscle cells.

The concentration of calcium helps in the contraction and relaxation of muscles. During depolarization, the calcium concentration increases that change conformation of troponin and tropomyosin and allows the actin to bind with myosin, resulting into relaxation of the muscle cell.

Hence, the correct option is "B. muscle relaxation".