An engineer is designing surfаce electrоdes tо recоrd electricаl signаls from the heart. She notices that the ECG signal amplitude (1 mV) is much smaller than the action potential recorded directly from a single heart cell (100 mV). How does the volume conductor model explain this dramatic amplitude reduction? The thoracic tissues act as electrical insulators, blocking most of the signal Surface electrodes are less sensitive than microelectrodes The action currents spread through the resistive thoracic medium, distributing the potential over a large volume The heart's electrical activity decreases naturally as it propagates outward