Stimulating neurons

In vivo, neurons are excited either through the cascade of synaptic inputs onto their cell and dendrites body from other neurons or through receptor potentials generated through sensory organs. The Neurophysiologists often stimulate a neuron straight via injecting an electrical current into it through a stimulating microelectrode. The stimulator generally delivers a square wave current pulse. There are three variables can  be altered at will on  most stimulators that are: the  duration of the  pulse the  amplitude of the  injected current and  the  frequency of the  pulses. The way of the current that is defined as the flow of positive charge determines the response of the neuron. If a little inward current is injected into a cell it will become a little more inside positive. This is reduce in the membrane potential because Vm gets closer to zero and is called a depolarization. If, alternatively an outward current is injected (that is if current is withdrawn from the cell) then the membrane potential increases; that is called hyperpolarization. The sizes and time courses of depolarizing and hyperpolarizing potentials seen in nerve cell injected with small currents are determined solely by the passive electrical properties of the neuron.