Anatomy and Physiology Notes: Conduction System of the Heart

   Key Concepts

1. The electrical activity of cardiac cells is caused by the selective opening and closing of plasma membrane channels for sodium, potassium, and calcium ions.

2. Depolarization is achieved by the opening of sodium and calcium channels and the closing of potassium channels.

3. Repolarization is achieved by the opening of potassium channels and the closing of sodium and calcium

channels.

4. Pacemaker potentials are achieved by the opening of channels for sodium and calcium ions and the closing of channels for potassium ions.

5. Electrical activity is normally initiated in the sinoatrial (SA) node where pacemaker cells reach threshold first.

6. Electrical activity spreads across the atria, through the atrioventricular (AV) node, through the Purkinje system, and to ventricular muscle.

7. Norepinephrine increases pacemaker activity and the speed of action potential conduction.

8. Acetylcholine decreases pacemaker activity and the speed of action potential conduction.

9. Voltage differences between repolarized and depolarized regions of the heart are recorded by an electrocardiogram (ECG).

10. The ECG provides clinically useful information about rate, rhythm, pattern of depolarization, and mass of electrically active cardiac muscle.

Pathway

SA Node

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Walls of the Atrium (Atrial Contraction)

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AV Node

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Delay in transmission

(To provide ample time for ventricular filling)

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Bundle of His

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Left and Right Bundle Branch

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Purkinje Fibers

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Ventricular Contraction