Cardiac Conduction & Action Potentials Video

Video at a Glance

• The heart implements the cardiac conduction system to coordinate the myocardium’s actions so the chambers contract in an organized fashion, allowing the heart to operate as a pump.
• Myocardial cells generate and propagate action potentials.
• In a normal, healthy heart, action potentials start in the SA node and then travel from the left atrium to the right atrium and the AV node.
• Action potential transmission speed varies across fibers, and the AV node slows the conduction of the action potential, creating an AV node delay.
• AV node delays present on an EKG between the P wave and QRS complex.
• Action potentials occur when a process opens up a sodium channel, and sodium rushes into the cell, decreasing the positive charge outside the cell and increasing the positive charge inside the cell. That impulse is then propagated along the cell, creating an action potential.
• Nerve cell action potential has two phases: fast sodium influx and fast potassium efflux.
• Cardiac myocyte action potential has four phases: fast sodium influx, fast sodium efflux, slow calcium influx plateau, and slow calcium channel closing.
• Faster or slower heart rate depends on the speed of sodium influx through sodium channels.