Put in correct order the sequence in which excitation would move through the conducting system of the heart:
1. Purkinje fibers
2. AV bundle
3. AV node
4. SA node
5. bundle branches
A. $1,4,3,2,5$.
B. $4,3,2,5,1$.
C. $4,2,3,5,1$.
D. $3,5,4,2,1$.
E. $3,2,4,5,1$.
Answer (1)
The heart's electrical activity starts at the SA node.
The impulse travels to the AV node, then the AV bundle.
Next, it goes to the bundle branches and finally to the Purkinje fibers.
The correct sequence is 4 , 3 , 2 , 5 , 1 .
Explanation
Understanding the Heart's Conducting System The heart's conducting system initiates with the sinoatrial (SA) node, which is the heart's natural pacemaker. From the SA node, the electrical impulse travels to the atrioventricular (AV) node. After a slight delay at the AV node, the impulse moves to the AV bundle (also known as the bundle of His), then to the bundle branches, and finally to the Purkinje fibers, which distribute the impulse to the ventricular myocardium, causing ventricular contraction.
Determining the Correct Sequence Based on the above understanding, the correct sequence is: SA node (4) -> AV node (3) -> AV bundle (2) -> bundle branches (5) -> Purkinje fibers (1).
Identifying the Correct Option Therefore, the correct order is 4, 3, 2, 5, 1.
Examples
Understanding the sequence of excitation in the heart is crucial in diagnosing and treating heart conditions. For instance, an electrocardiogram (ECG) measures the electrical activity of the heart and can reveal abnormalities in the conduction pathway. Knowing the correct sequence helps doctors identify where the electrical signal is disrupted, leading to appropriate interventions such as medication or pacemaker implantation to restore normal heart rhythm and function. This knowledge is also fundamental in understanding arrhythmias and other cardiac disorders.
