Cardiac Conducting System

Overview

• The heart has its own built-in electrical system called the cardiac conducting system.
• It produces electrical impulses that signal the heart muscles to contract.
• This system can be influenced by external factors like the nervous system and hormones.

Types of Cardiac Muscle Cells

1. Autorhythmic Cells

   • Control, regulate, and coordinate the heartbeat through electrical activity.
   • Have the ability to stimulate heart contraction without external influence.
   • Two main types:
     • Pacemaker Cells: Generate electrical impulses.
     • Conducting Cells: Distribute these impulses throughout the heart.

2. Contractile Cells

   • These cells contract to produce the force needed to pump blood.

Autorhythmicity

• Refers to the heart's ability to contract on its own without neural or hormonal input.
• Nervous and endocrine systems can still influence the heart's rate and strength of contraction.

Pacemaker Cells

• Located in the SA Node (Sinoatrial Node) and AV Node (Atrioventricular Node).
• SA Node: Primary pacemaker, sets the heart rate (60-100 beats per minute).
• AV Node: Secondary pacemaker, fires at 40-60 beats per minute.

Conducting Pathways

• Internodal Pathways: Connect the SA Node to the AV Node.
• AV Bundle (Bundle of His): Pathway from AV Node.
• Bundle Branches: Split from AV bundle to carry impulses down the interventricular septum.
• Purkinje Fibers: Spread throughout the ventricles causing contraction.

Electrical Impulse Propagation

• Depolarization: Causes generation of an action potential.
• Repolarization: Cells reset for another action potential.

ECG/EKG

• Measures electrical activity of the heart.
• P Wave: Atrial depolarization.
• PR Interval: Delay at AV Node.
• Q Wave: Beginning of ventricular depolarization.
• QRS Complex: Ventricular depolarization and contraction.
• T Wave: Repolarization of ventricular cells.

Summary

• The SA Node initiates the heartbeat with electrical impulses.
• Signals travel through the internodal pathways to the AV node.
• AV Node delays, then fires impulses to the ventricles.
• Bundle branches and Purkinje fibers ensure ventricular contraction.
• ECG captures and displays the heart's electrical activity for monitoring.