The long central process of a neuron. A single axon extends from each cell body of the neuron to the synapse or end-organ and is responsible for the transmission of the nerve impulse. In humans and other vertebrates, most peripheral axons are sheathed in a fatty layer called myelin, which acts to insulate the axon from the surrounding tissue. There are regular breaks in the myelin sheathing, called the nodes of Ranvier, that allow the electrical impulses to jump from node to node (saltatory transmission) rather than transit in the axon via the slower chemical depolarization process.