electrode 1. a medium used between an electric conductor and the object to which the current is to be applied.   2. in electrotherapy or electrosurgery, an instrument with a point or surface from which to transmit an electric current to the body of a patient or to another instrument.      3. in electrodiagnosis, a needle or metal plate used to stimulate or record the electrical activity of tissue; see also lead2. active electrode, the electrode of an electrical therapeutic or surgical device through which electrical current is applied.in electromyography, an exploring electrode. bifilar needle electrode, bipolar needle e. bipolar needle electrode, a needle electrode consisting of two insulated wires inside a single cylinder, with neither one acting as the reference electrode; variations in voltage can be noted between the areas the wires touch. bipolar stimulating electrode, a stimulating electrode that has the two terminals attached together and near each other. calomel electrode, an electrode capable of both collecting and giving up chloride ions in neutral or acidic aqueous media, consisting of mercury in contact with mercurous chloride; used as a reference electrode in pH measurements. coaxial needle electrode, concentric needle e. concentric needle electrode, a recording electrode consisting of an insulated metal wire inside a hollow stainless steel cannula; differences in potential are measured using the needle shaft as reference and the wire tip as the exploring electrode. depolarizing electrode, an electrode that has a resistance greater than that of the portion of the body enclosed in the circuit. earth electrode, ground e. esophageal electrode, esophageal pill electrode, a pill electrode designed to lodge in the esophagus at the level of the atrium; it is used for obtaining esophageal electrograms and for delivering pacing stimuli. exploring electrode, in electrodiagnosis, the electrode, usually small, placed nearest to the site of the bioelectric activity being recorded; it determines the potential in only that localized area. ground electrode, an electrode that is connected to a ground; called also earth e. inactive electrode, in an electrocautery, the electrode through which current distributed through the active electrode is returned to the generator. indifferent electrode, reference e. monopolar needle electrode, a needle electrode consisting of a single piece of stainless steel wire coated with insulating material except at the tip; it must be accompanied by another electrode as a reference. monopolar stimulating electrode, a stimulating electrode that has the two terminals attached separately and relatively far apart. multilead electrode, an electrode composed of a number of insulated wires inside a metal cannula, with their bare tips at apertures flush with the outer circumference of the cannula; used to determine the territory of a motor unit. Called also multielectrode. needle electrode, a thin, cylindrical electrode with an outer shaft beveled to a sharp point, enclosing a wire or series of wires; needle electrodes are used to explore the activity of single motor or nerve units or stimulate them. patch electrode, a tiny electrode with a blunt tip, used in studies of membrane potentials. See also patch clamp and microelectrode. pill electrode, an electrode usually enclosed within a gelatin capsule and attached to a flexible slender wire so that it may be swallowed, such as an esophageal electrode. recording electrode, an electrode used to measure electric potential change in body tissue; for recording, two electrodes must be used, the exploring e. and the reference e. (qq.v.). reference electrode, an electrode whose placement is remote from the source of recorded activity, so that it is presumed to be at either a negligible or constant potential. scalp electrode, an electrode placed on or just below the surface of the scalp; the most common type used in electroencephalography. single fiber needle electrode, a needle electrode with a small recording surface for the recording of individual muscle fiber action potentials. See also single fiber electromyography. stimulating electrode, an electrode used to apply electric current to tissue; it must include both a negative terminal and a positive terminal. See also bipolar stimulating e. and monopolar stimulating e. surface electrode, one placed on the skin surface and used to stimulate or record electrical activity in the underlying tissue.