Question 1

Which of the following best describes the function of the intrinsic cardiac conduction system?

Accepted Answer

It coordinates the contraction of cardiac muscle cells to ensure efficient pumping of blood.

Question 2

Where are the primary pacemaker cells of the heart located?

Accepted Answer

In the sinoatrial (SA) node, located in the right atrium near the entrance of the superior vena cava.

Question 3

Which of the following best describes the role of pacemaker cells in the heart?

Accepted Answer

They spontaneously generate action potentials that initiate each heartbeat.

Question 4

During the depolarization phase of a cardiac pacemaker cell, which ion primarily enters the cell?

Accepted Answer

Calcium ($$\mathrm{Ca$$^{2+}$$})$$

Question 5

What is the correct sequence of structures that an electrical impulse travels through in the intrinsic cardiac conduction system?

Accepted Answer

SA node → AV node → Bundle of His → Right and Left Bundle Branches → Purkinje fibers

Question 6

Which ion leaves the cardiac pacemaker cell during repolarization, restoring the negative membrane potential?

Accepted Answer

Potassium ($$\mathrm{K^+})$$

Question 7

A patient has a damaged SA node. Which part of the intrinsic conduction system is most likely to take over as the pacemaker, and what is the expected heart rate range?

Accepted Answer

AV node; 40–60 beats per minute

Question 8

Which of the following best explains why the SA node is called the 'pacemaker' of the heart?

Accepted Answer

It has the fastest rate of spontaneous depolarization among all cardiac conduction cells.

Question 9

During the pacemaker potential (prepotential) phase in SA node cells, which ion channels are primarily responsible for the gradual depolarization?

Accepted Answer

Slow sodium ($$\mathrm{Na^+}) $$channels

Question 10

A drug that blocks calcium channels in pacemaker cells would most likely have which effect on the heart?

Accepted Answer

It would slow the heart rate by reducing the rate of depolarization.

Question 11

Which of the following best describes the difference between depolarization in cardiac pacemaker cells and contractile cardiac muscle cells?

Accepted Answer

Depolarization in pacemaker cells is primarily due to $$\mathrm{Ca$$^{2+}$$}$$ influx, while in contractile cells it is due to $$\mathrm{Na^+}$$ influx.

Question 12

If the Purkinje fibers become the dominant pacemaker of the heart, what is the expected intrinsic heart rate?

Accepted Answer

20–40 beats per minute

Question 13

Which of the following scenarios would most likely result in bradycardia (abnormally slow heart rate)?

Accepted Answer

Damage to the SA node causing the AV node to take over as pacemaker

Question 14

During repolarization of a cardiac pacemaker cell, which of the following best describes the movement of ions?

Accepted Answer

$$\mathrm{K^+}$$ ions move out of the cell, making the inside more negative.

Question 15

A patient is given a medication that increases the permeability of pacemaker cells to sodium ions during the pacemaker potential. What is the most likely effect on heart rate?

Accepted Answer

Heart rate will increase due to faster depolarization.

Cardiac Conduction System and Pacemaker Cell Physiology

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