Which sequence correctly describes skeletal muscle excitation-contraction coupling?

Which sequence correctly describes skeletal muscle excitation-contraction coupling?

• A. Electrical impulse causes Ca2+ release from SR, Ca2+ binds troponin C, tropomyosin shifts to expose myosin-binding sites.
• B. Extracellular Ca2+ triggers binding sites directly.
• C. Cross-bridge cycling occurs without Ca2+.
• D. Troponin T binds calcium to start contraction.

Answer: (A)