MEDICAL PHYSIOLOGY

Detailed explanation-1: -T-tubules are closely associated with a specific region of the SR, known as the terminal cisternae in skeletal muscle, with a distance of roughly 12 nanometers, separating them. This is the primary site of calcium release.

Detailed explanation-2: -sarcoplasmic reticulum, intracellular system of closed saclike membranes involved in the storage of intracellular calcium in striated (skeletal) muscle cells.

Detailed explanation-3: -Depolarization of the sarcolemma (muscle membrane) caused by nerve stimulation causes calcium ions to be released from the sarcoplasmic reticulum.

Detailed explanation-4: -Terminal cisternae are basically the enlarged portions of the sarcoplasmic reticulum (SR), where the intercellular Ca2+ is stored. Interposed between the SR and the T-tubule are dihydropyridine receptors and ryanodine receptors, which, upon activation, allow the release of Ca2+ from the SR into the sarcoplasm.

Detailed explanation-5: -The concentration of calcium within muscle cells is controlled by the sarcoplasmic reticulum, a unique form of endoplasmic reticulum in the sarcoplasm. Muscle contraction ends when calcium ions are pumped back into the sarcoplasmic reticulum, allowing the muscle cell to relax.