An action potential is (chemical or electrical) in nature. The neuron is more (- or +) inside because of negatively charged molecules like on the inside and cations like outside. As the neuron fires, there’s a temporary reversal in as the axon undergoes (depolarization or repolarization) as flow into the cell. The action potential travels down the , sending a signal down it. The whole thing takes about 1/1,000th of a .