thaler chapter 1

1   The Basics

14

A pacemaker cell depolarizing spontaneously.

If we record one electrical cycle of depolarization and repolarization from a single cell, we obtain an electrical tracing called an action potential . With each spontaneous depolarization, a new action potential is generated, which in turn stimulates neighboring cells to depolarize and generate their own action potential, and so on and on, until the entire heart has been depolarized.

Maximum voltage at peak depolarization

Resting potential

A typical action potential.

The action potential of a cardiac pacemaker cell looks a little different than the generic action potential shown here. A pacemaker cell does not have a true resting potential. Its electrical charge drops to a minimal negative potential of approximately −60 mV, which it maintains for just a moment (it does not rest there), and then gradually rises until it reaches the threshold for the sudden depolarization that is an action potential. These events are illustrated on the following tracing.