Q92: The Ca?* released from the sarcoplasmic reticulum begins the contraction... - Muscle Physiology - Veterinary Physiology- ICAR JRF/SRF 2024 | Agrigyan

• Excitation-Contraction Coupling in Striated Muscle: Depolarization of T-tubules activates dihydropyridine receptors (DHPR), opening ryanodine receptors (RyR1) to release $Ca^{2+}$ from the sarcoplasmic reticulum.
• Molecular Trigger: Free cytosolic $Ca^{2+}$ binds to Troponin C (TnC), inducing a conformational shift that pulls tropomyosin out of the myosin-binding groove on F-actin filaments, thereby exposing actin cross-bridge binding sites to allow myosin head binding and power-stroke execution (Option 3).

Correct option: (3) Exposing actin filament cross-bridge binding sites