He most important factor in decreasing the intracellular concentration of calcium ion after contraction is

A) active transport of calcium across the sarcolemma.

B) active transport of calcium into the sarcoplasmic reticulum.

C) active transport of calcium into the synaptic cleft.

D) diffusion of calcium out of the cell.

E) diffusion of calcium into the sarcoplasmic reticulum

B. Active transport of calcium into the sarcoplasmic reticulum.

Explanation:

Calcium ions (Ca2+) are released from sarcoplasmic reticulum during the onset of muscle contraction. This increases the intracellular concentration of calcium ions.

The propagation of last action potential through T tubule is followed by active pumping of calcium ions from sarcoplasm to back to the sarcoplasmic reticulum by Ca2+-ATPase pumps. This pumping of calcium ions back to the sarcoplasmic reticulum lower down the intracellular calcium ion concentration after muscle contraction.