MUSCLE PHYSIOLOGY

Detailed explanation-1: -The main function of the SR is to store calcium ions (Ca2+). Calcium ion levels are kept relatively constant, with the concentration of calcium ions within a cell being 10, 000 times smaller than the concentration of calcium ions outside the cell.

Detailed explanation-2: -The sarcoplasmic reticulum (SR) constitutes the main intracellular calcium store in striated muscle and plays an important role in the regulation of excitation-contraction-coupling (ECC) and of intracellular calcium concentrations during contraction and relaxation.

Detailed explanation-3: -Calcium ions are stored inside the sarcoplasmic reticulum. When an action potential arrives, calcium ions are released from the sarcoplasmic reticulum into the sarcoplasm around the thick and thin filaments. The calcium ions then bind with troponin, which causes a change in the shape of the troponin molecule.

Detailed explanation-4: -Calcium ions at rest are stored in the sarcoplasmic reticulum (SR) from which they are rapidly released upon the depolarisation of the sarcolemmal and transverse (T-) tubular membranes of the muscle cell.