Final answer:
An action potential represents a change in the electrical charge across a neuron's membrane, occurring when a neuron is actively transmitting a nerve impulse. It involves depolarization due to the influx of sodium ions and differs from the resting potential, which is the neuron's non-active state.
Step-by-step explanation:
When a neural impulse is occurring within a neuron, we say that an action potential is occurring. An action potential is a rapid change in the electrical charge across a neuron's membrane, which constitutes the nerve impulse that travels down the neuron's axon. This process starts when the neuron receives a signal, leading to the opening of sodium channels and the influx of sodium ions, thereby depolarizing the neuron. The reversal from a negative to a positive charge inside the neuron is what characterizes an action potential.
The resting potential is the state of the neuron when it is not transmitting signals, maintained by the sodium-potassium pump, and characterized by a negative charge inside the neuron in comparison to the outside.