Final answer:
Upon the arrival of an action potential at the axon terminal, voltage-gated Ca2+ channels open, allowing calcium ions to enter and induce neurotransmitter release.
Step-by-step explanation:
When the action potential reaches the axon terminal, it triggers the opening of voltage-gated calcium channels (Ca2+). These channels allow Ca2+ ions to flow into the cell. The influx of calcium ions initiates a cascade of events that leads to the fusion of synaptic vesicles with the presynaptic membrane, resulting in the release of neurotransmitters into the synaptic cleft. This process is crucial for the transmission of the electrical signal from one neuron to another or to a target cell, such as a muscle fiber.