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Difficulty: MediumCirculatory and Transport Systems in Animals

During a cardiac cycle in a mammal, an electrical impulse originates and spreads through specialized conductive tissues to coordinate heart contractions. Which of the following represents the correct sequential path of the electrical excitation wave from its origin to ventricular contraction?

  1. 1Initiation of an electrical impulse at the sinoatrial (SA) node in the right atrial wall.
  2. 2Spread of the depolarization wave across the atrial myocardium to the atrioventricular (AV) node.
  3. 3Transmission of the signal down the Bundle of His along the interventricular septum.
  4. 4Rapid distribution of excitation through the Purkinje fibers throughout the ventricular myocardium.

Answer

The correct sequence of cardiac electrical conduction is: Sinoatrial (SA) node initiation → Atrioventricular (AV) node excitation → Bundle of His transmission → Purkinje fibers distribution.
The myogenic initiation of heart contraction begins at the sinoatrial (SA) node, known as the pacemaker, located in the right atrium. Electrical depolarization spreads across the atrial myocardium to cause atrial systole while reaching the atrioventricular (AV) node. After a short delay at the AV node that permits blood to flow into the ventricles, the impulse travels rapidly through the Bundle of His along the interventricular septum. Finally, the signal spreads through the Purkinje fibers embedded in the ventricular walls, triggering coordinated ventricular systole.

Step-by-Step Solution

1
Identify the origin of the myogenic cardiac impulse.
The impulse originates at the sinoatrial (SA) node located in the wall of the right atrium.
The SA node acts as the natural pacemaker initiating each heart contraction.
2
Trace the path of atrial excitation to the secondary conductive node.
The wave of depolarization spreads across both atria to the atrioventricular (AV) node.
This wave triggers atrial contraction (systole) while conveying the signal toward the ventricles.
3
Follow the passage of the signal down the central cardiac septum.
From the AV node, the electrical signal passes down the Bundle of His situated in the interventricular septum.
The signal is briefly delayed at the AV node before being directed rapidly down the septum toward the apex.
4
Determine the final conductive pathway causing ventricular contraction.
The Bundle of His divides into Purkinje fibers, spreading excitation upward through the ventricular myocardium.
Purkinje fibers deliver the electrical wave to the ventricular muscle fibers, stimulating synchronized ventricular contraction.

Key Concept

Cardiac Conduction System and Path of Electrical Excitation
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Topics

Circulatory and Transport Systems in Animals

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