Final answer:
Action potentials trigger the release of neurotransmitters at the axon terminal, affecting the postsynaptic cell by either increasing or decreasing its likelihood to fire an action potential depending on whether the neurotransmitters are excitatory or inhibitory.
Step-by-step explanation:
When action potentials arrive at the axon terminal, they depolarize the membrane and lead to the opening of voltage-gated Na+ channels. This results in further depolarization, which causes voltage-gated Ca²+ channels to open. Elevated calcium ion levels inside the axon terminal trigger the fusion of synaptic vesicles to the presynaptic membrane, releasing neurotransmitters into the synaptic cleft.
The neurotransmitters diffuse across the narrow space and bind to receptors on the postsynaptic cell. If the neurotransmitter is excitatory, it causes excitatory postsynaptic potentials (EPSPs), depolarizing the membrane of the postsynaptic cell and making it more likely to fire an action potential. Conversely, neurotransmitters that are inhibitory will cause inhibitory postsynaptic potentials (IPSPs), hyperpolarizing the postsynaptic cell and making it less likely to fire an action potential.