Interactive Physiology
Cardiac Action Potential
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Benjamin Cummings Publishing Co (http://www.awl.com/bc)
Page 1. Introduction
• The coordinated contractions of the heart result from electrical changes that take place in cardiac
cells.
Page 2. Goals
• To understand the ionic basis of the pacemaker potential and the action potential in a cardiac
autorhythmic muscle cell.
• To understand the ionic basis of an action potential in a cardiac contractile (ventricular) cell.
• To understand that autorhythmic and contractile cells are electrically coupled by current that flows
through gap junctions.
Page 3. Intrinsic Conduction System
• Cardiac autorhythmic cells in the intrinsic conduction system generate action potentials that spread
in waves to all the cardiac contractile cells. This action causes a coordinated heart contraction. Of
all the cells in the body, only heart cells are able to contract on their own without stimulation
from the nervous system.
Page 4. Gap Junctions
• Action potentials generated by autorhythmic cells create waves of depolarization that spread to
contractile cells via gap junctions.
• Label the parts of this diagram:
Page 5. Depolarization vs. Repolarization
• If depolarization reaches threshold, the contractile cells, in turn, generate action potentials, first
depolarizing then repolarizing. After depolarization, the cardiac myofibrils in contractile cells
slide over each other resulting in muscle contraction. After repolarization these cells relax.
** You may repeat the animation again if you wish by clicking on the autorhythmic cell again.
** Now is a good time to go to quiz question 1:
• Click the Quiz button on the left side of the screen.
• After answering question 1, click the Back to Topic button on the left side of the screen.
• To get back to where you left off, click on the scrolling page list at the top of the screen and choose "6.
Autorhythmic Cell Anatomy".
