Question 1

Which structure in cardiac muscle cells is primarily responsible for rapid transmission of electrical impulses between cells?

Accepted Answer

Gap junctions

Question 2

Cardiac muscle cells have a high energy demand. Which molecule is the primary source of energy for contraction, and which organelle is most abundant to support this demand?

Accepted Answer

ATP; Mitochondria

Question 3

The sinoatrial (SA) node is known as the heart's pacemaker. What property allows it to set the pace for the heart, and which ion channel is most responsible for this property?

Accepted Answer

Spontaneous depolarization; Funny (If) sodium channels

Question 4

Arrange the following in the correct order of electrical conduction in the heart: 1) AV node, 2) Purkinje fibers, 3) SA node, 4) Bundle of His. Which step is crucial for delaying ventricular contraction?

Accepted Answer

3, 1, 4, 2; AV node

Question 5

During the action potential of a contractile cardiomyocyte, which phase is responsible for the influx of calcium ions, and what is the main source of this calcium?

Accepted Answer

Phase 2 (plateau); Sarcoplasmic reticulum and extracellular fluid

Question 6

Which part of the ECG corresponds to atrial depolarization?

Accepted Answer

P wave

Question 7

If the AV node conduction is abnormally slow, what would be the expected effect on the ECG?

Accepted Answer

Prolonged PR interval

Question 8

During ventricular systole, which valves are open and which are closed?

Accepted Answer

Atrioventricular valves closed; Semilunar valves open

Question 9

A patient has a mutation that impairs the function of desmosomes in cardiac muscle cells. What is the most likely consequence?

Accepted Answer

Weakened mechanical connection between cells

Question 10

Which equation best represents the relationship between cardiac output, heart rate, and stroke volume?

Accepted Answer

$$CO = HR 	imes SV$$

Question 11

Which of the following best explains why cardiac muscle cells have more mitochondria than skeletal muscle cells?

Accepted Answer

Cardiac muscle cells require more ATP for continuous contraction

Question 12

During the cardiac cycle, which phase is characterized by isovolumetric contraction, and what is happening to the valves during this phase?

Accepted Answer

Ventricular systole; All valves are closed

Question 13

Which ion is primarily responsible for the rapid depolarization phase (Phase 0) of the cardiac action potential in contractile cells?

Accepted Answer

Sodium (Na	extsuperscript{+})

Question 14

A patient presents with a heart rate of 40 bpm and an absent P wave on ECG. Which pacemaker is most likely controlling the heart rhythm?

Accepted Answer

Atrioventricular (AV) node

Question 15

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

Accepted Answer

They provide both mechanical and electrical connection between cells

Question 16

If extracellular calcium is removed, what effect would this have on the action potential of contractile cardiomyocytes?

Accepted Answer

Shortened plateau phase due to reduced calcium influx

Question 17

Which channel type is most responsible for the pacemaker potential in autorhythmic cells?

Accepted Answer

Funny (If) sodium channels

Question 18

During which phase of the cardiac cycle are both the atrioventricular and semilunar valves closed?

Accepted Answer

Isovolumetric contraction

Question 19

Which of the following best explains the importance of the delay at the AV node?

Accepted Answer

It allows the atria to contract and empty blood into the ventricles before ventricular contraction

Question 20

A patient with hyperkalemia (elevated K	extsuperscript{+} in the blood) is likely to experience which effect on cardiac action potentials?

Accepted Answer

Decreased resting membrane potential, leading to impaired depolarization

Cardiac Muscle and the Cardiac Cycle: Structure, Function, and Electrophysiology

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