Overview
This lecture discusses the structure and function of the heart’s electrical conduction system, focusing on the propagation of action potentials and the mechanisms that coordinate the cardiac cycle.
Cardiac Conduction System Structure
- The heart’s conduction system ensures synchronized contraction of atria and ventricles.
- Key components include the sinoatrial (SA) node, atrioventricular (AV) node, AV bundle (bundle of His), bundle branches, and Purkinje fibers.
- The SA node, located in the right atrium, acts as the heart’s natural pacemaker.
Propagation of Action Potentials
- The SA node generates spontaneous action potentials at regular intervals.
- Action potentials spread quickly across atrial muscle, causing atrial contraction.
- The AV node slows the impulse, allowing atria to finish contracting before ventricles contract.
- Impulses travel from the AV node down the bundle of His, through bundle branches, and into Purkinje fibers for rapid ventricular depolarization.
Coordination of the Cardiac Cycle
- Atrial systole (contraction) occurs before ventricular systole due to conduction timing.
- This sequence ensures efficient blood flow from atria to ventricles before ventricular contraction.
- Electrical and mechanical events are tightly coordinated for optimal cardiac output.
Key Terms & Definitions
- Sinoatrial (SA) node — cluster of pacemaker cells in the right atrium that initiates the heartbeat.
- Atrioventricular (AV) node — node that delays impulses, enabling atrial contraction before ventricles.
- Bundle of His (AV bundle) — pathway for impulses from AV node into ventricles.
- Purkinje fibers — fibers that spread the impulse rapidly through the ventricular myocardium.
Action Items / Next Steps
- Review diagrams of the heart’s conduction system.
- Read textbook section on cardiac electrical activity.
- Prepare questions on impulse propagation for next class discussion.