The extracellular field potential is the electrical potential produced by cells, e.g. nerve or muscle cells, outside of the cell. Electrophysiological studies investigate these potentials using extracellular microelectrodes. In these experiments the extracellular field potential will be detected as an electrical potential whose source and composition is often ambiguous, making its interpretation difficult. Individual nerve cells neurons may produce spikes seen as peaks of some tens to hundreds of microvolts. Contributions from neighboring neurons may overlap, producing extracellular potentials of up to several millivolts. Spatially integrating over even larger populations of cells, i.e. lumps of nervous or muscular tissue, will produce signals commonly called local field potentials (LFP) that can be recorded either in the tissue or with suitable equipment at the body surface as, e.g., electroencephalogram (EEG), electrocardiogram (ECG), or electromyogram (EMG).
For individual cells, the time course of the extracellular potential theoretically is inversely proportional to the transmembrane current. In practice, however, this is complicated considerably by the very complex morphology of neurons and the overlap of contributions from adjacent cells.
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