The action potential that is established in the stimulated membrane area disturbs the neighboring area, leading to its depolarization.
The stimulus thus causes a wave of depolarization and repolarization that propagates along the plasma membrane of the neuron. This wave of propagation is the nervous impulse.
The nerve impulse propagates in one direction in the nerve fiber. Dendrites always drive the impulse toward the cell body. The axon, in turn, drives the impulse toward the extremities, that is, away from the cell body.
All or nothing law
Stimulation of a neuron follows the law of all or nothing. This means that either the stimulus is intense enough to excite the neuron, unleashing the action potential, or nothing happens. There is no stronger or weaker action potential; it is equal regardless of the stimulus intensity. The smallest stimulus capable of generating action potential is called threshold stimulus.