Question 1

Which structure in cardiac muscle cells is responsible for allowing ions to pass directly from cell to cell, enabling the myocardium to function as a single unit?

Accepted Answer

Gap junctions

Question 2

During the cardiac cycle, what event causes the first heart sound (LUBB) that can be heard with a stethoscope?

Accepted Answer

Closure of the atrioventricular (AV) valves

Question 3

Which node acts as the natural pacemaker of the heart, initiating each heartbeat and setting the pace for the heart rate?

Accepted Answer

Sinoatrial (SA) node

Question 4

What is the primary reason cardiac muscle cells are self-excitable and can initiate their own depolarization?

Accepted Answer

Their plasma membranes are more 'leaky' to sodium and calcium ions

Question 5

Which phase of the cardiac cycle is characterized by the ventricles being completely closed chambers, with all valves shut and no change in blood volume?

Accepted Answer

Isovolumetric ventricular contraction

Question 6

What is the typical resting membrane potential of cardiac contractile cells?

Accepted Answer

$$-90\ 	ext{mV}$$

Question 7

Which component of the cardiac conduction system delays the electrical impulse, allowing the atria to complete their contraction before the ventricles contract?

Accepted Answer

AV node

Question 8

In an ECG, which wave corresponds to ventricular depolarization and precedes ventricular contraction?

Accepted Answer

QRS complex

Question 9

What is the main energy source used by cardiac muscle cells for ATP production, even when other fuels are available?

Accepted Answer

Fatty acids

Question 10

Which of the following best describes the function of desmosomes in cardiac muscle cells?

Accepted Answer

Prevent separation of adjacent cells during contraction

Question 11

During ventricular ejection, what pressure does the aorta typically reach?

Accepted Answer

$$120\ 	ext{mmHg}$$

Question 12

Which interval on an ECG represents the time from the beginning of atrial excitation to the beginning of ventricular excitation?

Accepted Answer

P-R interval

Question 13

What is the effect of the sympathetic nervous system on heart rate?

Accepted Answer

Increases heart rate

Question 14

Which of the following is TRUE regarding the refractory period in cardiac muscle?

Accepted Answer

It lasts nearly as long as the contraction, preventing tetanic contractions

Question 15

A patient’s ECG shows absent P waves and a heart rate of 45 beats/min. Which rhythm is most likely present?

Accepted Answer

Junctional rhythm

Question 16

Which event marks the beginning of ventricular systole in the cardiac cycle?

Accepted Answer

Closure of AV valves

Question 17

If the Purkinje fibers are damaged, which of the following is most likely to occur?

Accepted Answer

Ventricular contraction is uncoordinated and inefficient

Question 18

Which of the following best explains why the heart cannot operate effectively with a significant oxygen debt?

Accepted Answer

Cardiac muscle relies almost exclusively on aerobic respiration

Question 19

What is the total time elapsing between initiation of the impulse by the SA node and depolarization of the last ventricular muscle cells in a healthy human heart?

Accepted Answer

$$0.22\ 	ext{seconds}$$

Question 20

Which of the following would most likely diminish heart contractile activity?

Accepted Answer

Interference with calcium binding or movement through calcium channels

Cardiac Muscle, Conduction System, Electrocardiography, and Cardiac Cycle

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