MICROANATOMY

Detailed explanation-1: -The endoplasmic reticulum in the muscle fiber is known as sarcoplasmic reticulum. It stores calcium ions which regulate the muscle contraction.

Detailed explanation-2: -Correct answer: Calcium is stored in the sarcoplasmic reticulum, awaiting a signal for release into the cytoplasm. Explanation: Calcium is stored in the sarcoplasmic reticulum at high concentrations.

Detailed explanation-3: -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-4: -Calcium diffusing in the cytoplasm between myosin and actin filaments of the muscle fibrils causes the filaments to slide into each other, triggering the contraction of the entire muscle fiber.