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Difficulty: HardHuman Anatomy and Body Systems

During a healthy cardiac cycle, electrical impulses coordinate the synchronized contraction of the heart chambers. Place the following anatomical structures in the correct chronological sequence through which an action potential travels during a single heartbeat, from initial pacemaking to complete ventricular excitation.

  1. 1Sinoatrial (SA) node initiates spontaneous rhythmic depolarization in the right atrium
  2. 2Atrioventricular (AV) node receives the impulse and introduces a brief conduction delay
  3. 3Bundle of His (atrioventricular bundle) conducts the action potential across the fibrous cardiac skeleton
  4. 4Right and left bundle branches propagate the impulse downward through the interventricular septum toward the apex
  5. 5Purkinje fibers distribute the excitation upward throughout the lateral ventricular myocardium

Answer

The correct sequence of cardiac conduction is: Sinoatrial (SA) node → Atrioventricular (AV) node → Bundle of His → Right and left bundle branches → Purkinje fibers.
Cardiac excitation begins in the sinoatrial node, passes across the atria to the atrioventricular node where it is briefly delayed, travels across the fibrous skeleton via the Bundle of His, descends the interventricular septum through the left and right bundle branches, and finishes by spreading through the Purkinje fiber network to trigger upward ventricular contraction.

Step-by-Step Solution

1
Identify the primary electrical source of the heartbeat.
The Sinoatrial (SA) node in the superior wall of the right atrium fires spontaneously to start the cycle.
The SA node possesses the highest intrinsic rate of autorhythmicity.
2
Trace the impulse from atrial myocardium to the junctional tissue.
The Atrioventricular (AV) node captures the wave and slows transmission.
The AV nodal delay ensures mechanical filling of the ventricles is complete prior to systole.
3
Follow the impulse through the non-conducting fibrous barrier.
The Bundle of His bridges the insulating tissue into the upper septum.
Direct electrical crossover between atria and ventricles is blocked except through this bundle.
4
Track propagation toward the base and apex along the septum.
The impulse splits into the right and left bundle branches traveling down the septum.
Splitting ensures coordinated and bilateral delivery of the wave to both ventricles.
5
Identify terminal distribution throughout the ventricular walls.
Purkinje fibers spread the signal upward through the contractile ventricular myocardium.
Terminal Purkinje arborization initiates ventricular ejection from the apex toward the outflow tracts.

Key Concept

Cardiac Conduction System Pathway and Electrophysiology
Estimated Time:1m 30s
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Topics

Human Anatomy and Body Systems

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