Synaptic vesicles at the neuromuscular junction contain . View Available Hint(s)for Part B calcium acetylcholine ACh receptors synaptic potentials Part C ACh receptors are found mainly in the . View Available Hint(s)for Part C terminal cisternae axon terminal sarcolemma synaptic vesicles Part D What most directly causes synaptic vesicles to release acetylcholine into the synaptic cleft