The axon, or nerve fiber, is an extension of the neuron that drives the electrical signal from the cell body to the synaptic zones. Along the axon, this signal consists of action potentials.
The other extensions of the neuron are the dendrites that lead the signal from the synapses to the cell body (to be then driven to the axon). The neurons most often have a single axon and several dendrites (the influx can come from several directions, or several dendrites, but always converge towards the axon).
