Which sequence correctly describes excitation-contraction coupling from motor neuron to muscle contraction?

• A. Calcium ions are released within the muscle fibers before any neural input, initiating contraction.
• B. ACh release occurs after a muscle action potential travels along the sarcolemma.
• C. Ca2+ binds troponin and triggers contraction directly, without ACh or neural signaling.
• D. Motor neuron action potential triggers ACh release; ACh binds receptors on the sarcolemma; sarcolemma action potential travels along T-tubules; Ca2+ released from the sarcoplasmic reticulum; Ca2+ binds troponin; tropomyosin moves; cross-bridge cycle; contraction.

Answer: (D)