19.6c Conduction System of the Heart: Spread of the Action Potential

After starting at the SA node, what happens to the action potential?

After starting at SA node the action potential (AP) spreads

What is step 1 of AP spread?

AP is distributed through atria, reaches AV node

How does excitation travel through the atria?

Excitation travels via gap junctions

What happens to the atria during step 1?

Two atria contract together

What is step 2 of AP spread?

AP is delayed at the AV node

Why are AV nodal cells slow?

Due to small diameter and few gap junctions

Why is the AV node the only pathway for conduction to the ventricles?

Insulation of fibrous skeleton means AV node is bottleneck and only path

What is the purpose of the delay at the AV node?

Delay allows ventricles to fill before they contract

What is step 3 of AP spread?

AP travels through AV bundle to Purkinje fibers

What is the conduction pathway after the AV node?

AV node → AV bundle → bundle branches → Purkinje fibers

What is step 4 of AP spread?

AP spreads through ventricles

How does the impulse spread through ventricular muscle?

Gap junctions allow impulse to spread through cardiac muscle fibers

What is the result of AP spread through the ventricles?

Cells of the two ventricles contract nearly simultaneously