Final answer:
An action potential arriving at the axon terminal causes the opening of Ca2+ channels, leading to neurotransmitter release. Calcium ions trigger the fusion of synaptic vesicles with the presynaptic membrane, facilitating the communication between neurons.
Step-by-step explanation:
The action potential reaches the axon terminal of the sending cell, causing calcium ions (Ca2+) to flow into the synaptic end bulb of the sending cell through the Ca2+ channels. When an action potential arrives at the axon terminal, it triggers the opening of voltage-gated sodium (Na+) channels, allowing sodium ions to enter the cell, which further depolarizes the presynaptic membrane.
This depolarization prompts voltage-gated calcium channels to open. The influx of calcium ions inside the cell is crucial as it initiates a signaling cascade that results in the fusion of synaptic vesicles, containing neurotransmitters, with the presynaptic membrane. These neurotransmitters are then released into the synaptic cleft through exocytosis, carrying the signal to the next neuron.