The following are definitions of common terms referring to types of electrical stimulation (commonly applied in organ bath experiments).
1) FIELD STIMULATION
The stimulation is applied over a general field/area and the response is evoked by this electromagnetic field. This kind of stimulation is commonly applied to smooth muscle.
2) POINT STIMULATION
The stimulation is directly applied to a specific focal point. A response is evoked by this local charge and the stimulus spreads from one excitable cell to another (through the sarcolemma or adjacent cell membranes). This type of stimulation is commonly applied to isolated hearts, skeletal muscle and isolated nerve.
3) CONSTANT CURRENT STIMULATION
The stimulus current is gradually increased until an optimum response is evoked from the tissue. The stimulus is then maintained at this level. If measuring the voltage responses from the tissue, then the tissue impedance/resistance can be calculated using Ohm's law.
4) CONSTANT VOLTAGE STIMULATION
The stimulus voltage is gradually increased until a tissue response is induced. However, the current is not controlled. Therefore, the current may change as a result of variable tissue impedance during the experiment and the number of electrical charges supplied to the tissue is not uniform.
NOTE: Constant current stimulation is preferable to constant voltage because the exact current resulting in electrical excitation is known.
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