Overview
This lecture explains the heart's conduction system, focusing on how electrical signals coordinate cardiac muscle contractions and the sequence of atrial and ventricular systole and diastole.
Conduction System Overview
- The heart's contraction is triggered by electrical stimulation, essential for pumping blood effectively.
- The conduction system ensures the heart works in coordinated cycles, alternating between contraction (systole) and relaxation (diastole).
Major Components and Pathway
- The sinoatrial (SA) node, located above the right atrium, initiates the electrical impulse (the "pacemaker").
- The SA node self-regulates (myogenic) and emits signals that spread across both atria, causing atrial systole (contraction).
- As the atria contract, blood is forced into the ventricles, while the ventricles are in diastole (relaxation).
- The electrical impulse then reaches the atrioventricular (AV) node, situated between the atria and ventricles.
- The AV node receives the signal from the SA node and relays it down the heart's septum.
- The bundle of His, located in the septum, separates the signal into left and right branches for each ventricle.
- The signal travels down the septum and up around the ventricles through Purkinje fibers (also called Perkinje/Purkinje fibers).
- Purkinje fibers distribute the signal to all cardiac muscle cells in the ventricles, causing coordinated ventricular systole (contraction).
- During ventricular systole, the atria go through diastole to refill with blood.
- The heart's contraction follows the "all or none" principle, meaning it contracts fully or not at all.
Key Terms & Definitions
- Sinoatrial (SA) node — The heart's pacemaker; initiates electrical impulses.
- Myogenic — Describes tissue that generates its own impulse without external stimulation.
- Atrial systole — Contraction of the atria, pushing blood into ventricles.
- Ventricular diastole — Relaxation of ventricles while atria contract.
- Atrioventricular (AV) node — Relays signals from atria to ventricles.
- Bundle of His — Conducting fibers in the septum that split the impulse to both ventricles.
- Purkinje fibers — Specialized fibers spreading the impulse throughout ventricular muscle.
- Ventricular systole — Contraction of ventricles, pumping blood into arteries.
- Atrial diastole — Relaxation of atria as ventricles contract.
- All or none law — The heart contracts fully with each stimulus or not at all.
Action Items / Next Steps
- Review diagrams of the conduction system for visual understanding.
- Study the phases of the cardiac cycle, linking them to the conduction pathway.