What triggers neurotransmitter release at the synapse?

The release of neurotransmitters at the synapse is primarily triggered by the action potential depolarizing the axon terminal. When an action potential travels down the axon and reaches the axon terminal, it causes a rapid depolarization of the terminal membrane. This depolarization opens voltage-gated calcium channels, allowing calcium ions to flow into the neuron. The influx of calcium ions is the crucial signal that initiates the process of neurotransmitter release from synaptic vesicles into the synaptic cleft.

Once the neurotransmitters are released, they can bind to receptors on the postsynaptic neuron, leading to various physiological effects. However, it is the action potential's depolarization of the axon terminal that is the initial and necessary trigger for this release to occur.