an action potential (also known as a nerve impulse or spike) is a pulse-like wave of voltage that travels along several types of cell membranes.
An action potential proper is generated by the opening of voltage-gated sodium channels located at a region of the neuron called the 'axon hillock'.
How is action potential generated
In its cell membrane.
When a stimulus stimulates a neuron above the threshold, the action potential is generated.
ganglion cells