Cardiovascular Physiology Concepts
Richard E. Klabunde, Ph.D.
|
|
|
Action Potentials
Many cells in the body have the ability to undergo a transient depolarization and repolarization that is either triggered by external mechanisms (e.g., motor nerve stimulation of skeletal muscle or cell-to-cell depolarization in the heart) or by intracellular, spontaneous mechanisms (e.g., cardiac pacemaker cells). There are two general types of cardiac action potentials. Non-pacemaker action potentials, also called "fast response" action potentials because of their rapid depolarization, are found throughout the heart except for the pacemaker cells. The pacemaker cells generate spontaneous action potentials that are also termed "slow response" action potentials because of their slower rate of depolarization. These are found in the sinoatrial and atrioventricular nodes of the heart.
RK Revised 04/06/07 |
|
DISCLAIMER: These materials are for educational purposes only, and are not a source of medical decision-making advice. © 1999-2008 Richard E. Klabunde, all rights reserved. |
Both
types of action potentials in the heart differ considerably from action
potentials found in neural and skeletal muscle cells. One major difference
is in the duration of the action potentials. In a typical nerve, the
action potential duration is about 1 ms. In skeletal muscle cells, the
action potential duration is approximately 2-5 ms. In contrast, the
duration of cardiac action potentials range from 200 to 400 ms. Another
difference between cardiac and nerve and muscle action potentials is the role of
calcium ions in depolarization. In nerve and muscle cells, the
depolarization phase of the action potential is caused by an opening of sodium
channels. This also occurs in non-pacemaker cardiac cells. However,
in cardiac