What is the electrical signal called that travels along an axon to trigger neurotransmitter release?

The electrical signal that travels along an axon to trigger neurotransmitter release is known as the action potential. This is a rapid and large change in the membrane potential that occurs when a neuron is sufficiently stimulated. The action potential propagates along the axon due to the opening and closing of voltage-gated ion channels, allowing sodium ions to flow into the neuron and depolarize the membrane. Once the action potential reaches the axon terminals, it causes the release of neurotransmitters into the synaptic cleft, allowing communication with adjacent neurons.

The other terms refer to different aspects of neuronal signaling: resting potential is the stable, negative charge of a neuron when it is not actively transmitting a signal; graded potential refers to changes in membrane potential that vary in size and do not reach the threshold to trigger an action potential; synaptic potential is the change in membrane potential of a postsynaptic neuron in response to neurotransmitter release, but it is not the signal propagating along the axon itself.