We have discussed the production of local circuit currents as a consequence of membrane activation and the role these currents play in propagation of excitation. Because such currents flow, in part, in the extracellular medium they may be detected with extracellular electrodes or even body surface electrodes. The electrocardiogram is a familiar such example: The sources of these body surface potentials are the combined action currents of many cardiac cells. The goal of this chapter is to describe mathematical relations that link the cellular action potential with the volume conductor fields (action current fields) associated with them. Such quantitative relationships permit an examination of the “inverse” process where from extracellular measurements one may deduce the behavior of underlying cells. This would be valuable for both basic research as well as for clinical studies.
KeywordsField Point Source Density Axial Dipole Cylindrical Fiber Propagate Action Potential
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