Final answer:
Action potentials trigger the release of neurotransmitters from axon terminals into the synaptic cleft, which may bind to postsynaptic receptors resulting in excitatory postsynaptic potentials (EPSPs) if they are excitatory in nature.
Step-by-step explanation:
The 'action potentials' mentioned in the question refer to the electrical signals transmitted by neurons. When an action potential is fired, it travels along the neuron's axon to the axon terminals. At the terminals, the arrival of the action potential triggers the opening of voltage-gated Ca2+ channels, leading to an influx of Ca2+ ions. These ions facilitate the fusion of neurotransmitter-containing vesicles with the presynaptic membrane and thus the release of neurotransmitter into the synaptic cleft.
At a chemical synapse, neurotransmitters can then bind to receptors on the postsynaptic neuron, leading to either excitatory or inhibitory effects. Excitatory neurotransmitters, like acetylcholine at the neuromuscular junction, open sodium channels allowing Na+ to enter the postsynaptic cell, causing depolarization and an excitatory postsynaptic potential (EPSP), which increases the likelihood of the postsynaptic neuron firing an action potential if the depolarization is above the threshold.