When an action potential arrives at a synapse, what happens fi rst? A. a neurotransmitter is released into the synaptic cleft B. extracellular Na + crosses the post-synaptic membrane C. Choline in the synaptic cleft enters the nerve cell and is converted to acetyl choline D. extracellular Ca ++ enters the nerve cell
Option D. When an action potential arrives at a synapse, then extracellular Ca++ enters the nerve cells.
