Cardiac electrophysiology: Membrane potential, action potential, automaticity and electrical vectors
The action potential includes a depolarization (activation) followed by a repolarization (recovery). The action potential occurs in all cardiac cells but its appearance varies depending on cell type. During de- and repolarization ions (Na+ [sodium], K+ [potassium] and Ca2+ [calcium]) flow back and forth across the cell membrane. Because ions are electrically charged, their movement generates an electrical current. This means that the propagation (spread) of the action potential is equal to the spread of an electrical current. All tissues and fluids surrounding the heart have an abundance of ions, which means that they can act as electrical conductors. Consequently, the electrical currents generated in the myocardium are transmitted all the way to the skin, where they can be detected by electrodes. The electrocardiograph (ECG machine) records and processes these electrical currents and presents them as the electrocardiogram (ECG). As mentioned earlier, the electrical potentials of the …
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