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Why does the impulse pause about 100 ms at the atrioventricular node?
ATo let the ventricles refill with blood
BTo let the atria finish pumping before the ventricles fire
CTo let the SA node recharge its sodium channels
DTo protect the Purkinje fibers from fatigue
Answer & Solution
Correct answer: B. To let the atria finish pumping before the ventricles fire
1. At the AV node there is a delay of approximately 100 ms.
2. The delay allows the atria to complete pumping blood before the impulse is transmitted onward.
3. Firing the ventricles too early would waste the atrial contribution to filling.
_Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 19 "The Cardiovascular System: The Heart", section 19.2 Cardiac Muscle and Electrical Activity_
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