Describe the sequence from motor neuron action potential to calcium release from the sarcoplasmic reticulum in skeletal muscle.

Describe the sequence from motor neuron action potential to calcium release from the sarcoplasmic reticulum in skeletal muscle.

• A. Motor neuron AP triggers ACh release; ACh binds receptors causing depolarization; depolarization travels along the sarcolemma and down T-tubules; Ca2+ is released directly from the SR in response to the depolarization.
• B. Motor neuron AP triggers ACh release; Ca2+ is released from the SR via DHPRs without involvement of RyR; contraction occurs.
• C. Ca2+ triggers neurotransmitter release to NMJ; ACh binds receptors causing depolarization; contraction occurs.
• D. Motor neuron AP triggers ACh release; ACh binds receptors causing depolarization; depolarization travels along the sarcolemma and down T-tubules; voltage-gated DHPRs detect change and trigger RyR channels on the SR to release Ca2+ into cytoplasm; Ca2+ binds troponin leading to contraction.

Answer: (D)