Question 1

A major difference between cardiac muscle cells and the cells in the cardiac conducting system is that the contractile cells do not undergo spontaneous depolarization.

Accepted Answer

The answer of A major difference between cardiac muscle cells...

Question 2

The QRS wave of the ECG corresponds to depolarization of the atria.

Accepted Answer

The QRS wave of the ECG corresponds to depolarization of the ventricles, not the atria.

Question 3

An ectopic pacemaker is an area of the myocardial conducting system, other than the atrioventricular node, that initiates cardiac depolarization.

Accepted Answer

The answer of An ectopic pacemaker is an area of...

Question 4

Normal heart sounds are produced by vibrations caused by the closing of the AV valves at the end of diastole and the closing of the aortic and pulmonary valves at the end of systole.

Accepted Answer

This statement is true. The closure of the heart valves produces vibrations that are heard as the familiar "lub-dub" sounds of the heartbeat. The first heart sound (lub) is caused by the closing of the mitral and tricuspid valves at the end of diastole, while the second heart sound (dub) is caused by the closing of the aortic and pulmonary valves at the end of systole.

Question 5

Long-term studies show that the risk for heart attack and stroke doubles for every 20 mm increase in diastolic pressure and 10 mm Hg in systolic pressure.

Accepted Answer

This statement is true. Long-term studies have shown a correlation between increasing blood pressure and an increased risk for cardiovascular events such as heart attack and stroke. Specifically, for every 20 mm Hg increase in diastolic pressure and every 10 mm Hg increase in systolic pressure, the risk for these events doubles.

Question 6

The myocardial cells receive their blood supply from the coronary arteries that branch off from the aorta.

Accepted Answer

The statement is correct. The coronary arteries are responsible for delivering oxygenated blood to the myocardial cells of the heart.

Question 7

The left ventricle has a thicker wall than the right ventricle because the left ventricle has to pump blood against a higher pressure.

Accepted Answer

The left ventricle pumps blood to the entire body, including the systemic circulation, which has a higher pressure than the low-pressure pulmonary circulation served by the right ventricle. This requires the left ventricle to have a thicker and more muscular wall in order to generate enough force to pump blood against this higher pressure.

Question 8

Stimulation of parasympathetic nerves releases epinephrine into the blood plasma.

Accepted Answer

Stimulation of parasympathetic nerves does not release epinephrine. Instead, it is released by the adrenal gland and sympathetic nerves.

Question 9

The only time during the cardiac cycle that the AV valves are open is systole.

Accepted Answer

The AV valves are actually open during diastole, allowing blood to flow from the atria into the ventricles. They close during systole to prevent blood from flowing back into the atria.

Question 10

Sympathetic stimulation of the heart increases action potential conduction velocity through the AV node.

Accepted Answer

Sympathetic stimulation leads to increased release of norepinephrine, which increases the conduction velocity through the AV node. This allows for faster transmission of the cardiac action potential and faster heart rate.

Question 11

The left ventricle has to pump more blood than the right ventricle because the left ventricle has to pump blood through the systemic circulation, which is much larger than the pulmonary circulation.

Accepted Answer

The answer of The left ventricle has to pump more...

Question 12

The determinant of whether heart valves are open or closed is the pressure difference across them.

Accepted Answer

The pressure difference across heart valves determines whether they are open or closed. When the pressure on one side of the valve is greater than the pressure on the other side, the valve opens. When the pressure on one side is lesser than the pressure on the other side, the valve closes.

Question 13

The wave of ventricle free wall contraction starts at the apex of the heart and travels toward the base.

Accepted Answer

This is known as the ventricular depolarization wave or QRS complex on an ECG. It starts at the apex of the heart and moves upwards towards the base.

Question 14

Cardiac muscle cannot undergo tetanus because its absolute refractory period lasts almost as long as the muscle twitch.

Accepted Answer

This statement is true. Cardiac muscle has a long absolute refractory period, which means that it cannot be stimulated again until the previous contraction has completed. This makes it impossible for cardiac muscle to undergo tetanus, which is a sustained contraction caused by rapid stimulation.

Question 15

Sympathetic stimulation of cardiac muscle cells produces stronger and faster contractions because proteins that pump Ca²⁺ out of the cell are inhibited, which reduces Ca²⁺ concentration in the sarcoplasm.

Accepted Answer

Sympathetic stimulation actually increases the concentration of Ca2+ in the sarcoplasm by enhancing the influx of Ca2+ through voltage-gated Ca2+ channels and by promoting the release of Ca2+ from the sarcoplasmic reticulum. This increased Ca2+ concentration leads to stronger and faster contractions of cardiac muscle cells. The proteins that pump Ca2+ out of the cell are not inhibited but rather function to maintain the proper balance of Ca2+ concentration in the cell.

Question 16

The inherent pacemaker discharge rate of the sinoatrial node is 72 beats per minute.

Accepted Answer

The inherent pacemaker discharge rate of the sinoatrial node is not a fixed rate but varies depending on the physiological conditions. However, the average pacemaker discharge rate in healthy adults is around 60-100 beats per minute.

Question 17

During most of systole, left ventricular pressure exceeds aortic pressure, causing blood ejection.

Accepted Answer

During systole, the left ventricle contracts and generates pressure that exceeds the pressure in the aorta, causing blood to be ejected from the left ventricle into the aorta. This is known as systolic blood pressure. However, towards the end of systole, aortic pressure may start to exceed left ventricular pressure, causing the aortic valve to close and preventing the backflow of blood into the left ventricle.

Question 18

An electrocardiogram would be definitive for diagnosing diseases involving the valves of the heart.

Accepted Answer

An electrocardiogram (ECG) records the electrical activity of the heart, but it cannot definitively diagnose diseases involving the heart valves. Other diagnostic tests, such as echocardiography or cardiac catheterization, may be needed for a definitive diagnosis.

Question 19

The sinoatrial node is normally the heart's pacemaker because it has the fastest spontaneous rate of diastolic depolarization.

Accepted Answer

The sinoatrial node is located in the right atrium and has the fastest spontaneous depolarization rate, which sets the tempo for the rest of the heart's rhythm.

Question 20

Parasympathetic neurons release acetylcholine onto cells in the atria of the heart, but not onto cells of the ventricles.

Accepted Answer

This is because parasympathetic neurons only innervate the SA node and AV node, which are located in the atria of the heart, and do not directly stimulate the ventricles.

Quiz 12: Cardiovascular Physiology