How does the all-or-none law work for nerve cells?

An action potential occurs if a stimulus is above a certain threshold. Once an action potential is triggered, a neuron transmits a signal down an axon, away from the neuronal cell body and toward the synapse, which is the point where neurotransmission occurs. 

The action potential is always a full response when stimulated by an action potential. There is no midway, nor is there such a thing as a weak or strong action potential. A stimulus always triggers an all-or-none process. This is an inbuilt protective mechanism that minimizes the possibility of losing any information along the way, ensuring that people are always able to respond appropriately to environmental stimuli.