What is the role of the calcium ion in the signaling of an action potential at the neuromuscular junction?

• A. Calcium moves across the synaptic cleft to relay the signal to the muscle tissue.
• B. Calcium causes the muscle cell to depolarize propagating the action potential.
• C. Calcium is important for contraction in the sarcomere; it does not play a role at the axon terminal.
• D. Calcium entering the axon terminal triggers the release of Acetylcholine into the synaptic cleft.