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: -Troponin binds to tropomyosin and helps to position it on the actin molecule; it also binds calcium ions. To enable a muscle contraction, tropomyosin must change conformation, uncovering the myosin-binding site on an actin molecule and allowing cross-bridge formation.

Detailed explanation-3: -Troponin plays an important role during excitation-contraction coupling. During excitation, calcium ions bind to TnC; it interacts with tropomyosin to unblock active sites between the myosin filament and actin allowing cross-bridge cycling and thus contraction of the myofibrils that constitute the systole.

Detailed explanation-4: -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.