MEDICAL PHYSIOLOGY

Detailed explanation-1: -In these cells, the sarcoplasm ic reticulum sequesters calcium ions and thereby maintains low calcium concentrations in the sarcoplasm. Upon excitation and depolarization of the cell, the calcium channel opens and admits a small amount of calcium associated with the shift in the membrane potential.

Detailed explanation-2: -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.

Detailed explanation-3: -Ca2+ ions trigger muscle contraction and the release of Ca2+ from the sarcoplasmic reticulum (the intracellular Ca2+ storage site) plays an important role in determining the intramuscular Ca2+ concentration.

Detailed explanation-4: -Ionized calcium plays an important function in muscle contraction. Skeletal muscle function is governed by an action potential that releases calcium stored in the sarcoplasmic reticulum.

Detailed explanation-5: -The sarcoplasmic reticulum (SR) is a specialized form of the endoplasmic reticulum of muscle cells, dedicated to calcium ion (Ca2+) handling, necessary for muscle contraction and relaxation.