ABSTRACT
Neurophysiologists often stimulate a neuron directly by injecting an electrical current into it via a stimulating microelectrode. Three variables can be altered at will on most stimulators: the duration of the pulse, the amplitude of the injected current, and the frequency of the pulses. The direction of the current determines the response of the neuron. The sizes and time courses of depolarizing and hyperpolarizing potentials seen in nerve cells injected with small currents are determined solely by the passive electrical properties of the neuron. If a sufficiently large inward current is injected into a neuron its membrane potential will depolarize enough to generate an action potential. Under physiological conditions action potentials are triggered at the axon hillock and are propagated along the axon towards its terminals. All action potentials are about the same size regardless of the amplitude of the stimulus.
