Final answer:
A neurotransmitter must cross the synaptic gap to affect the action potential in a receiving neuron. It is released from the axon terminal and binds to receptors on the postsynaptic neuron, causing either an excitatory or inhibitory effect.
Step-by-step explanation:
To excite or inhibit an action potential in a receiving neuron, a neurotransmitter must cross the synaptic gap. This process begins when an action potential reaches the axon terminals of a neuron. Here, voltage-gated Ca2+ channels open, causing neurotransmitter-containing vesicles to merge with the presynaptic membrane and release neurotransmitter molecules into the synaptic cleft. The neurotransmitters then travel across this small gap and bind to receptors on the postsynaptic neuron. Depending on the type of neurotransmitter released, the response in the receiving neuron can be either excitatory, leading to depolarization, or inhibitory, causing hyperpolarization, thus affecting the potential for an action potential in the postsynaptic neuron.