Final answer:
An action potential arriving at the axon terminal causes voltage-gated calcium channels to open, leading to the release of neurotransmitters from synaptic vesicles into the synaptic cleft.
Step-by-step explanation:
When an action potential reaches the axon terminal, it triggers a complex series of events that lead to communication with a postsynaptic cell. The arrival of the action potential depolarizes the axon terminal membrane, causing voltage-gated sodium (Na+) channels to open.
This leads to further depolarization, which then triggers the opening of voltage-gated calcium channels (Ca2+). Calcium ions (Ca2+) entering the presynaptic cell initiate a signaling cascade that results in the fusion of synaptic vesicles with the presynaptic membrane. These vesicles contain neurotransmitters, which are then released into the synaptic cleft.
The neurotransmitter diffuses across the synaptic cleft and binds to receptor proteins on the membrane of the postsynaptic cell. Binding of neurotransmitters to these receptors can change the electrical state of the postsynaptic cell, potentially leading to a new action potential if the signal is strong enough. This process effectively converts the electrical signal of the action potential into a chemical signal and then back into an electrical signal in the postsynaptic cell, allowing for communication between neurons or between neurons and other cells, such as muscle cells in neuromuscular junctions.