Human Anatomy and Physiology: Cardiovascular System

Focus: The Conduction System of the Heart

Key Concepts:

• Conduction System: Essential for heart rhythm.
• SA Node: Initiates intrinsic rhythm.
• Pathway: SA node → AV node → AV bundle → Right/Left Bundle Branches → Purkinje fibers.
• Regulation: Neural and endocrine systems, but the heart can initiate its own action potential.

Components:

• SA Node:
  • Located in the right atrium.
  • Sets heart rate, initiates contraction.
• AV Node:
  • Receives signals from the SA node.
• Bundle Branches & Purkinje Fibers:
  • Spread impulse throughout myocardium.

Action Potential:

• Phases:
  • Prepotential phase (slow Na+ influx).
  • Rapid Ca2+ influx and K+ outflux.
• Plateau Phase: Extended refractory period for effective contraction.

Cardiac Muscle Cells:

• Structure:
  • Sarcomeres and T-tubules for impulse transmission.
  • Mitochondria for energy.
  • Intercalated discs with gap junctions and desmosomes.

Cardiac Cycle

Electrical Impulse Pathway:

1. SA Node: Initiates action potential.
2. AV Node: Short delay allows atrial contraction.
3. AV Bundle and Branches: Impulse travels to heart apex.
4. Purkinje Fibers: Spread impulse to ventricular walls for contraction.

Contraction Pattern:

• Simultaneous Atria Contraction → Ventricular Contraction
• Left & Right Ventricles: Contract together.

Electrocardiogram (ECG)

Key Components:

• P-Wave: Atrial depolarization → Atrial contraction.
• QRS Complex: Ventricular depolarization (includes atrial repolarization).
• T-Wave: Ventricular repolarization.

ECG and Cardiac Cycle Correlation:

• P-Wave: Initiates atrial contraction.
• QRS Complex: Initiates ventricular contraction.
• T-Wave: Indicates ventricular repolarization.

Refractory Periods:

• Absolute: No new action potential possible.
• Relative: New potential possible but unlikely.

Conclusion

• The conduction system ensures coordinated contraction for effective blood pumping.
• ECG provides insight into electrical activity corresponding to the heart's mechanical events.