MCAT Biology Question 92: Answer and Explanation
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Question: 92
2. Which of the following is the correct sequence of a cardiac impulse?
- A. SA node → AV node → Purkinje fibers → bundle of His → ventricles
- B. AV node → bundle of His → Purkinje fibers → ventricles → atria
- C. SA node → atria → AV node → bundle of His → Purkinje fibers → ventricles
- D. SA node → AV node → atria → bundle of His → Purkinje fibers → ventricles
Correct Answer: C
Explanation:
An ordinary cardiac contraction originates in, and is regulated by, the sinoatrial (SA) node. The impulse travels through both atria, stimulating them to contract simultaneously. The impulse then arrives at the atrioventricular (AV) node, which momentarily slows conduction, allowing for completion of atrial contraction and ventricular filling. The impulse is then carried by the bundle of His and its branches through the Purkinje fibers in the walls of both ventricles, generating a strong contraction.