Answer: pre-synaptic neuron
Explanation:
A pre-synaptic neuron is a neuron that produces the neurotransmitters in response to the action potential entering into the axon terminal. The vesicles present in the synapse forms the synaptic pool for the exocytosis of the neurotransmitters, which means they are readily releasable.
When the action potential reaches up to the nerve terminal the electrical signals will be generated at the voltage-gated calcium ion channels.