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Eleclrital Activity of the Heart

CARDIOYASCULAR PHYSIOLOCY

Aclion Potential of SA Node Cells

Potential

(mV)

Action Potential of Ventricular Myocytes

Figurę 4.5 Eiectrical Activitv of the Heart_

The normal pumping of blood through the chambers of tho hoait requires the precisely timed spread of action potential?. through the hearfs conduction system and the atrial and ventricular muscle. The rato of the heartbeat is set by spontaneously generated action polen-tials in the cells ot the SA node. The frequency of SA node action potentials is regulated by the autonomie nervous system. Sympa-thetic stimulation of the SA node inereases i, (principally Na' current)

and ir._v’-* which depolanzes the celi, and thereby inereases the heart ratę. Parasympathetic stimulation inereases \_K . which hyperpolanze the celi and thereby decreases the heart ratę. The venlricular musi I-action potential has a prolonged depolarization phase resulting fror Ca-' influx. This long plateau phase prevents tetany of cardiai mus cle at very high heart rates.

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