Q: Which of the following formulas correctly represents cardiac output ($$CO$$)?

$$CO = \text{Stroke Volume} \times \text{Heart Rate}$$

Question 1

Which of the following best explains why cardiac muscle cells cannot undergo summation of force like skeletal muscle cells?

Accepted Answer

The long refractory period due to the plateau phase prevents new action potentials until contraction is complete.

Question 2

During the plateau phase of the cardiac myocyte action potential, which ion movement is primarily responsible for maintaining depolarization?

Accepted Answer

Influx of calcium through L-type calcium channels

Question 3

Which of the following is a unique feature of cardiac muscle excitation-contraction coupling compared to skeletal muscle?

Accepted Answer

Calcium influx from the extracellular space triggers further calcium release from the sarcoplasmic reticulum.

Question 4

A patient’s ECG shows a lack of P waves and a pause in all electrical activity, followed by a resumption of normal rhythm. What is the most likely explanation?

Accepted Answer

Sinus arrest due to SA node failure

Question 5

Which of the following best describes the role of the sodium-calcium exchanger (NCX) in cardiac myocytes?

Accepted Answer

It uses the sodium gradient to remove calcium from the cell in exchange for sodium influx.

Question 6

Which sequence correctly describes the normal conduction pathway of the cardiac action potential?

Accepted Answer

SA node → internodal pathways → AV node → AV bundle → Purkinje fibers → ventricular muscle

Question 7

Which of the following changes would most likely occur in the pacemaker potential of SA node cells under increased parasympathetic stimulation?

Accepted Answer

The membrane potential becomes hyperpolarized, and the slope of depolarization decreases.

Question 8

A patient’s ECG shows a rapid, regular rhythm with approximately 120 beats per minute, but all waves are present and coordinated. Which term best describes this condition?

Accepted Answer

Sinus tachycardia

Question 9

Which of the following best explains the Frank-Starling mechanism in the heart?

Accepted Answer

Increasing end-diastolic volume stretches the ventricle, resulting in a stronger contraction and increased stroke volume.

Question 10

Which of the following formulas correctly represents cardiac output ($$CO$$)?

Accepted Answer

$$CO = 	ext{Stroke Volume} 	imes 	ext{Heart Rate}$$

Question 11

Which of the following is true regarding the effect of sympathetic stimulation on the SA node?

Accepted Answer

It increases sodium and calcium permeability, causing the pacemaker potential to reach threshold more quickly.

Question 12

Which of the following best describes the function of intercalated discs in cardiac muscle?

Accepted Answer

They contain gap junctions that allow rapid electrical communication between cardiac muscle cells.

Question 13

A patient’s ECG shows multiple P waves for each QRS complex, with irregular timing between P waves and QRS complexes. Which condition is most likely present?

Accepted Answer

AV conduction block

Question 14

Which of the following statements about the action potential in autorhythmic (pacemaker) cells is correct?

Accepted Answer

There is no true resting membrane potential; the membrane potential gradually depolarizes after each repolarization.

Question 15

Which of the following best describes the effect of increased venous tone on cardiac output?

Accepted Answer

It increases the velocity of blood return to the heart, increasing end-diastolic volume and stroke volume.

Question 16

Which of the following is the primary reason the left ventricle is thicker than the right ventricle?

Accepted Answer

It pumps blood to the entire systemic circulation, requiring greater force.

Question 17

Which of the following events corresponds to the T wave on a normal ECG?

Accepted Answer

Ventricular repolarization

Question 18

Which of the following best describes the effect of acetylcholine on the SA node?

Accepted Answer

It increases potassium permeability, hyperpolarizing the membrane and slowing heart rate.

Question 19

Which of the following is a correct statement about the role of calcium in cardiac muscle contraction?

Accepted Answer

Calcium binds to troponin, initiating cross-bridge cycling between actin and myosin.

Question 20

Which of the following best explains why the Purkinje fibers can act as a backup pacemaker for the heart?

Accepted Answer

They can spontaneously depolarize at a rate of about 30 beats per minute if both the SA and AV nodes fail.

Cardiac Muscle Physiology, Conduction System, and Cardiac Output

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