Question 1

Which structure in the heart is primarily responsible for initiating the action potential that sets the heart rhythm?

Accepted Answer

Sinoatrial (SA) node

Question 2

Gap junctions in cardiac muscle tissue are essential for which of the following functions?

Accepted Answer

Permitting rapid conduction of action potentials between cardiac cells

Question 3

A patient’s ECG shows a prolonged PR interval. Which part of the cardiac conduction system is most likely malfunctioning?

Accepted Answer

Atrioventricular (AV) node

Question 4

Which of the following best describes the effect of sympathetic stimulation on the heart?

Accepted Answer

Increases heart rate by stimulating the SA and AV nodes

Question 5

During which phase of the cardiac cycle are both the atrioventricular (AV) and semilunar (SL) valves closed?

Accepted Answer

Isovolumetric contraction

Question 6

Which of the following correctly matches the cardiac conduction structure to its location?

Accepted Answer

Right and left bundle branches: septum

Question 7

Which ion movement is primarily responsible for the plateau phase in the action potential of cardiac contractile cells?

Accepted Answer

Influx of Ca\^{2+} ions

Question 8

If potassium channels in cardiac contractile cells open sooner after depolarization, what would be the expected effect on the absolute refractory period?

Accepted Answer

Absolute refractory period would decrease

Question 9

Which of the following best describes the difference between the effect of the sympathetic and parasympathetic nervous systems on the heart?

Accepted Answer

Sympathetic increases heart rate and contractility, parasympathetic decreases heart rate

Question 10

Which event immediately follows the closure of the atrioventricular valves and coincides with the onset of ventricular systole?

Accepted Answer

Isovolumetric contraction

Question 11

Which phase of the cardiac cycle is associated with the second heart sound (S2)?

Accepted Answer

Isovolumetric relaxation

Question 12

Which of the following is a unique feature of cardiac pacemaker cells that allows them to be autorhythmic?

Accepted Answer

They spontaneously depolarize without external stimulation

Question 13

Which of the following best explains why the AV node conducts impulses more slowly than the SA node?

Accepted Answer

It ensures the atria have time to contract before the ventricles

Question 14

Which of the following is true regarding the opening of calcium ion channels in cardiac muscle cells?

Accepted Answer

They are voltage-gated

Question 15

On an ECG, which wave corresponds to atrial depolarization?

Accepted Answer

P wave

Question 16

Which of the following best describes the movement of ions during the plateau phase of a cardiac contractile cell action potential?

Accepted Answer

Ca\^{2+} influx and K\^+ efflux

Question 17

A patient’s ECG shows rapid, irregular QRS complexes with no distinct P waves. What is the most likely diagnosis?

Accepted Answer

Ventricular fibrillation

Question 18

Which of the following best describes the effect of increased permeability of the membrane to sodium ions in pacemaker cells?

Accepted Answer

The rate of depolarization increases

Question 19

Which phase of the cardiac cycle is characterized by ventricular pressure rising above atrial pressure, causing the AV valves to close but not yet opening the semilunar valves?

Accepted Answer

Isovolumetric contraction

Question 20

Which of the following statements about the cardiac cycle is true?

Accepted Answer

Isovolumetric contraction occurs when all valves are closed

The Heart: Electrical Conduction, Cardiac Action Potentials, Electrocardiogram, and Cardiac Cycle

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