Gr. 'running against'. Usually refers to nerve impulses which, traveling proximally along one branch of a Y-shaped sensory nerve fiber, arrive at the junction and travel distally along the other branch ( Ch. 9).
For most neurons, their dendrites, soma, or axons are depolarized forming an action potential that moves from the starting point of the depolarization toward the axons of the neuron. An antidromic impulse in an axon refers to conduction opposite to the normal, orthodromic direction.