Question 1

Which of the following best explains why cardiac muscle cannot sustain tetanic contractions, unlike skeletal muscle?

Accepted Answer

The long plateau phase in the cardiac action potential creates a prolonged absolute refractory period, preventing tetanus.

Question 2

A patient is experiencing rapid, irregular heart contractions that prevent effective pumping of blood. Which condition is most likely present, and what is the immediate danger?

Accepted Answer

Fibrillation; the ventricles are not pumping blood, risking cessation of circulation and brain death.

Question 3

During the pacemaker potential in SA node cells, which ion movement is primarily responsible for the slow depolarization toward threshold?

Accepted Answer

Influx of $$\mathrm{Na^+}$$ due to opening of slow sodium channels and reduced $$\mathrm{K^+}$$ efflux.

Question 4

Which of the following correctly matches the phase of the contractile cardiac muscle cell action potential with the predominant ion movement?

Accepted Answer

Plateau phase: $$\mathrm{Ca$$^{2+}$$}$$ influx through slow calcium channels.

Question 5

A patient’s ECG shows a prolonged delay between the P wave and the QRS complex. Which part of the conduction system is most likely responsible for this delay?

Accepted Answer

Atrioventricular (AV) node

Question 6

If the SA node fails to function, which structure typically takes over as the pacemaker, and what is the expected heart rate?

Accepted Answer

Atrioventricular (AV) node; 40–60 beats per minute

Question 7

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

Accepted Answer

It increases heart rate and force of contraction by releasing norepinephrine.

Question 8

During the action potential of a contractile cardiac muscle cell, which event is responsible for the rapid repolarization phase?

Accepted Answer

Inactivation of $$\mathrm{Ca$$^{2+}$$}$$ channels and opening of voltage-gated $$\mathrm{K^+}$$ channels, leading to $$\mathrm{K^+}$$ efflux.

Question 9

Which of the following statements about the cardiac conduction system is correct?

Accepted Answer

The AV bundle is the only electrical connection between the atria and ventricles.

Question 10

A patient consumes excessive caffeine, resulting in a region of the heart outside the SA node generating impulses more rapidly than the SA node. What is this phenomenon called?

Accepted Answer

Ectopic focus

Question 11

Which of the following best explains why the left side of the subendocardial conducting network (Purkinje fibers) is more elaborate than the right?

Accepted Answer

The left ventricle is larger and requires more extensive conduction to coordinate contraction.

Question 12

Which of the following is a direct consequence of the plateau phase in the cardiac action potential?

Accepted Answer

It ensures a long absolute refractory period, preventing tetanic contractions.

Question 13

Which of the following best describes the role of gap junctions in cardiac muscle?

Accepted Answer

They allow for rapid, coordinated spread of action potentials between cardiac muscle cells.

Question 14

A patient with a defective AV node is likely to experience which of the following?

Accepted Answer

Atrial and ventricular contractions become uncoordinated, possibly leading to heart block.

Question 15

Which of the following is true regarding the energy metabolism of cardiac muscle compared to skeletal muscle?

Accepted Answer

Cardiac muscle relies almost exclusively on aerobic respiration and cannot function long without oxygen.

Question 16

Which of the following best describes the sequence of excitation in the intrinsic cardiac conduction system?

Accepted Answer

SA node → AV node → AV bundle → bundle branches → Purkinje fibers

Question 17

Which of the following is the primary danger of an inadequate blood supply to the myocardium?

Accepted Answer

Lack of oxygen, since cardiac muscle relies on aerobic respiration.

Question 18

Which of the following best explains the effect of parasympathetic stimulation on the heart?

Accepted Answer

It decreases heart rate by releasing acetylcholine, primarily affecting the SA and AV nodes.

Question 19

During which phase of the pacemaker cell action potential does $$\mathrm{Ca$$^{2+}$$}$$ influx play the most significant role?

Accepted Answer

Depolarization phase, causing the rapid upstroke of the action potential.

Cardiac Electrophysiology and Conduction System: Study Notes for Anatomy & Physiology

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