The creation and conduction of action potentials represents a fundamental means of communication in the nervous system. Action potentials represent rapid reversals in voltage across the plasma membrane of axons. These rapid reversals are mediated by voltage-gated ion channels found in the plasma membrane. The distribution of voltage-gated channels along the axon enables the conduction of the action potential from the nerve cell body to the axon terminal. At the synapse, the electrical signal is converted to a chemical signal that is then propagated to the postsynaptic neuron.
When the neuronal membrane becomes depolarized, either via the delivery of an electric current or from a signal passing from an adjacent patch of membrane, voltage-gated sodium channels open and positively charged sodium ions—which are in much higher concentration outside of the cell—rush into the cell, producing a rapid reversal of the charge across the membrane. This spike of depolarization represents the action potential. The depolarization spreads to adjacent regions of the membrane, bringing these regions to threshold and thus propagating the signal along the axon. There is thus no loss of signal as an action potential travels along an axon.
When the axon potential reaches the nerve terminal, it triggers the release of neurotransmitter across the synaptic cleft, propagating the signal to the next neuron in the circuit.
Textbook Reference: Concept 34.2 Neurons Generate Electric Signals by Controlling Ion Distributions