Multiple Choice Questions (MCQs)
- What is the primary function of the SA node?
a) Conduct impulses to the ventricles
b) Act as the heart’s pacemaker
c) Delay impulse transmission
d) Conduct impulses through the Purkinje fibers
Answer: b) Act as the heart’s pacemaker - Where is the SA node located?
a) At the apex of the heart
b) In the ventricular septum
c) At the junction of the right atrium and cranial vena cava
d) On the inner wall of the left atrium
Answer: c) At the junction of the right atrium and cranial vena cava - What is the function of the AV node?
a) Generate rhythmical impulses
b) Delay impulse transmission to allow ventricular filling
c) Act as the primary pacemaker
d) Supply the ventricles with blood
Answer: b) Delay impulse transmission to allow ventricular filling - Which bundle resides on the inner wall of the left atrium?
a) Anterior pathway
b) Middle pathway
c) Posterior pathway
d) Bachmann’s bundle
Answer: d) Bachmann’s bundle - What are Purkinje fibers responsible for?
a) Generating rhythmical impulses
b) Rapid transmission of impulses to the ventricles
c) Delaying impulse transmission
d) Dividing the right and left ventricles
Answer: b) Rapid transmission of impulses to the ventricles - Where is the AV node located?
a) In the atrial walls
b) At the ventricular apex
c) In the septal walls of the right atrium near the tricuspid valve
d) Between the right and left atria
Answer: c) In the septal walls of the right atrium near the tricuspid valve - What is the role of transitional fibers?
a) Generate impulses in the atria
b) Connect internodal pathways to the AV node
c) Conduct impulses to the Purkinje fibers
d) Delay impulse transmission to the ventricles
Answer: b) Connect internodal pathways to the AV node - What separates the atria and ventricles electrically?
a) Fibrous tissue around the valves
b) Purkinje fibers
c) Bundle of His
d) Interatrial septum
Answer: a) Fibrous tissue around the valves - Which structure ensures simultaneous ventricular contraction?
a) SA node
b) AV node
c) Bundle of His and Purkinje fibers
d) Internodal pathways
Answer: c) Bundle of His and Purkinje fibers - What is the diameter range of SA node fibers?
a) 1–2 µm
b) 3–5 µm
c) 10–15 µm
d) 15–20 µm
Answer: b) 3–5 µm
Fill in the Blanks
- The SA node generates action potentials due to its low resting membrane potential of ________ mV.
Answer: -55 - The AV node is located cranio-dorsal to the ________ valve.
Answer: tricuspid - The ________ pathway conducts impulses from the SA node to the AV node.
Answer: internodal - Purkinje fibers terminate at the ________ of the heart.
Answer: ventricular apex - The ________ bundle divides into right and left branches that supply the ventricles.
Answer: Bundle of His
True or False
- The SA node has a low resting membrane potential, enabling automaticity.
Answer: True - The AV node is responsible for generating rhythmical impulses.
Answer: False - Purkinje fibers penetrate about one-third into the ventricular muscle mass.
Answer: True - The Bundle of His directly generates impulses in the ventricles.
Answer: False - Bachmann’s bundle is part of the posterior internodal pathway.
Answer: False
Subjective Questions
- Describe the functional significance of the delay in impulse transmission by the AV node.
Answer: The AV node delays impulse transmission to ensure that the atria contract completely before the ventricles begin to contract. This delay allows sufficient time for blood to move from the atria to the ventricles, ensuring optimal ventricular filling and efficient cardiac output. - Explain the role of Purkinje fibers in ventricular contraction.
Answer: Purkinje fibers form a network of conductive fibers that rapidly transmit impulses throughout the ventricular muscle. This ensures that the ventricles contract simultaneously and uniformly, generating sufficient pressure to eject blood into the pulmonary and systemic circulations efficiently.