Describe the generation of pacemaker action potentials and then track the resulting impulse through the cardiac conduction system. Include the names of specific types of channels in the first part of your answer

Question

What will be an ideal response?

Answer 1

The pacemaker cells in the SA node steadily depolarize spontaneously to near threshold as Na+ leaks into the cells through the If (funny channels). As the voltage nears threshold voltage, the If channels close and T-type Ca2+ channels open. Calcium ions diffusing into the cell through these channels brings the voltage to threshold, at which time the T-type channels close and L-type Ca2+ channels open. Enough Ca2+ ions pass into the cell through these channels to begin the impulse. Impulses spread out from the SA node and reach the contractile cells of the atria, which contract simultaneously. In addition, the impulse reaches the AV node and then passes into the AV bundle. From the AV bundle, the impulses passes along the bundle branches located in the septum between the two ventricles. From there, the impulse passes through the Purkinje fibers and spreads superiorly through the outer walls of the ventricles.