Bioelectromagnetism studies electric fields, electric currents and magnetic fields associated with living systems and their interaction with applied fields. Ionic currents across and along biological cell membranes generate measurable signals; the surrounding tissue conducts and redistributes them.
In electrocardiography, surface electrodes measure electric potential differences produced by distributed cardiac activity rather than directly recording one isolated cell. A volume conductor model relates internal source currents to those surface readings. Electrode position and conducting geometry matter, so a changed voltage can reflect source activity, measurement contact or the current paths through tissue.
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