MUSCLE PHYSIOLOGY

Detailed explanation-1: -The calcium ions released from endoplasmic reticulum72) bind to the calcium-binding subunit of troponin (troponin-C (TnC), ∼18 kDa), and the inhibition by troponin is neutralized to trigger muscle contraction.

Detailed explanation-2: -It binds with Troponin C and thus helps the myosin head to tighten onto the actin filament and to begin contraction of the muscles. Thus, the correct answer is option B. i.e., To bind with troponin, changing its shape so that the actin filament is exposed.

Detailed explanation-3: -Each heartbeat is triggered by a pulse of intracellular calcium ions which bind to troponin on the actin-containing thin filaments of heart muscle cells, initiating a change in filament structure that allows myosin to bind and generate force.

Detailed explanation-4: -Calcium triggers contraction by reaction with regulatory proteins that in the absence of calcium prevent interaction of actin and myosin. Two different regulatory systems are found in different muscles.

Detailed explanation-5: -Troponin (Tn) is the sarcomeric Ca2+ regulator for striated (skeletal and cardiac) muscle contraction. On binding Ca2+ Tn transmits information via structural changes throughout the actin-tropomyosin filaments, activating myosin ATPase activity and muscle contraction.