Page 142 - Physiology and Pathophysiology MNU 2024-2025 نظرى

Clinical pharmacy 2024/2025 Level 2 Pharm D Physiology and Pathophysiology (MD303)
Cardiac Electrophysiology

 Cardiac Muscle only contract when activated by electrical signals (the cardiac action potential)
The heart Consist of two Kind of Muscle cells.
1-Contractile cells 2-Conducting cells
✓ majority of Atrial & Ventricular tissue  They Conduct action potential over the entire myocardium.
✓ They Contract in response to electrical signal /Impulse  Able to generate action potential spontaneously

Conduction Pathway (The sequence of conduction)
1-Electrical Signals ➔ activate Cardiac Muscle ➔ Contract ➔ Cardiac action potential

1- Action Potential Spread from SA node to Right and left atria (via the Atrial intermodal

tracts) and to AV node.

2- Conduction is slowed in AV node to allow enough time for Ventricular filling.

3- The action potential ➔ conducted to bundle of His ➔ Rapidly Spread to Purkinje Fibers
➔ Cause both ventricle to contract at the same time.

Sequence of Action potential Spread:
1-Atria contract before Ventricle 2-Ventricles contract from apex to base for efficient
ejection of blood
 Rapid conduction of the action potential throughout the ventricles is essential and
allows for efficient contraction & ejection of blood

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