MEDICAL PHYSIOLOGY

Detailed explanation-1: -In cardiac muscle cells, calcium is an important effector of the coupling between cardiac depolarization (excitation) and cardiac contraction (called “excitation-contraction coupling”). In these cells, the sarcoplasm ic reticulum sequesters calcium ions and thereby maintains low calcium concentrations in the sarcoplasm.

Detailed explanation-2: -When the muscle is stimulated, calcium ions are released from its store inside the sarcoplasmic reticulum, into the sarcoplasm (muscle ).

Detailed explanation-3: -These include ryanodine receptor, a Ca2+ release channel which participates in Ca2+ release from sarcoplasmic reticulum into muscle cells, Ca2+-ATPase, which drives Ca2+ uptake, and calsequestrin that binds with Ca2+.

Detailed explanation-4: -In a muscle fibre, Ca++ is stored in the sarcoplasmic reticulum.

Detailed explanation-5: -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.