Biology Circulation / Transport MDCAT 2018
PMDC Verified Question 44 of 54
Which one of the following act as a pacemaker in heart?
A
Atria ventricular node
B
Sino-atrial node
C
Atria ventricular bundles of fibers
D
Bundle of His
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Sino-atrial node
Concept:

The natural pacemaker of the heart determines the baseline heart rate.

Formula:

None

Solution:

  • The Sino-atrial (SA) node spontaneously generates electrical impulses at a rate of \(70-80\) times per minute.


  • Because its intrinsic rate is the highest, it overrides other potential pacemakers and sets the rhythm for the entire heart.


Why other options are incorrect:

  • The AV node and Bundle of His can act as backup pacemakers if the SA node fails, but they operate at a much slower, secondary rate (\(40-60\) bpm).

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

Previous Question All Circulation / Transport MCQs Next Question

Want to solve full-length papers under timed exam conditions?

Practice with zero-scroll lockdown sprints, dynamic latency zone timers, live peer selection telemetry, and the automated Amber mistake recovery loop.

Enter Arena Sprint iOS App Android App