Heart Structure and Conduction System Practice Questions
20 free Heart Structure and Conduction System practice questions for the Physiology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following describes the correct order of electrical activation in the heart's conduction system?
- A SA node → AV node → Bundle of His → Purkinje fibers
- B SA node → AV node → Purkinje fibers → Bundle of His
- C AV node → SA node → Bundle of His → Purkinje fibers
- D SA node → Bundle of His → AV node → Purkinje fibers
Correct answer: SA node → AV node → Bundle of His → Purkinje fibers
The impulse begins at the SA node, travels through the atria to the AV node, enters the Bundle of His, and finally spreads through the Purkinje fibers. This sequence ensures the atria contract before the ventricles.
What is the primary physiological purpose of the 'AV nodal delay'?
- A To allow the atria to finish contracting and maximize ventricular filling
- B To allow the ventricles enough time to depolarize completely
- C To prevent the SA node from firing too rapidly during exercise
- D To ensure the aortic valve opens fully before the mitral valve closes
Correct answer: To allow the atria to finish contracting and maximize ventricular filling
The slow conduction through the AV node provides a delay of about 0.1 seconds. This allows the atria to pump their contents into the ventricles before ventricular contraction begins, optimizing cardiac output.
Which ion is primarily responsible for the 'Phase 0' upstroke of the action potential in SA nodal cells?
- A Fast Sodium (Na+) influx through voltage-gated channels
- B Potassium (K+) efflux through delayed rectifier channels
- C Calcium (Ca2+) influx through L-type channels in cardiac cells
- D Chloride (Cl-) influx through ligand-gated channels
Correct answer: Calcium (Ca2+) influx through L-type channels in cardiac cells
Unlike ventricular myocytes, SA nodal cells lack functional fast sodium channels. Their depolarization is driven by the relatively slow influx of calcium ions through L-type calcium channels.
The 'pacemaker potential' (Phase 4) in the SA node is largely attributed to the opening of which specific channels?
- A Funny channels (If) allowing sodium influx
- B Delayed rectifier potassium channels (IKr)
- C Inward rectifier potassium channels (IK1)
- D L-type calcium channels (ICa-L) opening
Correct answer: Funny channels (If) allowing sodium influx
Phase 4 is a slow, spontaneous depolarization toward the threshold. This is mediated by 'funny' sodium channels that open when the membrane potential is hyperpolarized, ensuring the heart beats automatically.
Which anatomical structure prevents the electrical impulse from spreading directly from the atria to the ventricles, except through the AV node?
- A The Interventricular septum wall
- B The Chordae tendineae attachments
- C The Fibrous skeleton of the heart
- D The Crista terminalis ridge structure
Correct answer: The Fibrous skeleton of the heart
The fibrous skeleton is a layer of dense connective tissue that acts as an electrical insulator. It forces the cardiac impulse to pass through the AV node/Bundle of His pathway, which is the only electrical bridge between the chambers.
Parasympathetic stimulation of the heart via the Vagus nerve primarily affects the SA node by:
- A Increasing the slope of the Phase 4 spontaneous depolarization
- B Opening more L-type calcium channels in the membrane
- C Shortening the absolute refractory period of the cell
- D Increasing potassium permeability and hyperpolarizing the cell
Correct answer: Increasing potassium permeability and hyperpolarizing the cell
Acetylcholine released by the vagus nerve opens K+ channels (GIRK), which hyperpolarizes the pacemaker cells and slows the rate of spontaneous depolarization. This results in a decreased heart rate (negative chronotropy).
Which part of the conduction system possesses the fastest conduction velocity (measured in m/sec)?
- A Atrial muscle
- B Atrioventricular node
- C Bundle of His
- D Purkinje fibers
Correct answer: Purkinje fibers
Purkinje fibers have a conduction velocity of approximately 2-4 m/sec. This rapid speed allows for nearly simultaneous contraction of all parts of the ventricular myocardium, ensuring efficient ejection of blood.
The 'Plateau Phase' (Phase 2) of a ventricular myocyte action potential is caused by the balance between:
- A Calcium influx and Potassium efflux
- B Sodium influx and Potassium efflux
- C Calcium influx and Sodium efflux
- D Chloride influx and Calcium efflux
Correct answer: Calcium influx and Potassium efflux
During Phase 2, the inward movement of calcium through L-type channels is balanced by the outward movement of potassium. This prolonged depolarization prevents tetany and allows time for the cardiac muscle to contract and relax.
In the event of a total SA node failure, which structure typically takes over as the secondary pacemaker?
- A Atrioventricular node
- B Purkinje fibers
- C Left Bundle Branch
- D Atrial internodal pathways
Correct answer: Atrioventricular node
The AV node has an intrinsic firing rate of about 40-60 beats per minute. If the SA node fails, the AV node assumes control as the 'nodal' or junctional pacemaker to maintain cardiac output.
The 'Bachmann Bundle' is a specialized conduction pathway that carries the electrical impulse to the:
- A Left Atrium
- B Right Ventricle
- C Aortic Arch
- D Coronary Sinus
Correct answer: Left Atrium
The Bachmann bundle (interatrial pathway) conducts the impulse from the right atrium to the left atrium. This ensures that both atria contract almost simultaneously.
Which of the following valves prevents the backflow of blood from the aorta into the left ventricle during diastole?
- A Mitral valve
- B Tricuspid valve
- C Aortic semilunar valve
- D Pulmonary semilunar valve
Correct answer: Aortic semilunar valve
The aortic semilunar valve closes at the end of ventricular systole when the pressure in the aorta exceeds the pressure in the left ventricle. This prevents blood from flowing backward into the heart.
The papillary muscles and chordae tendineae function to:
- A Directly pull the AV valves open during diastole
- B Close the semilunar valves during systole
- C Prevent AV valve prolapse into the atria during systole
- D Generate the force required for ventricular contraction
Correct answer: Prevent AV valve prolapse into the atria during systole
As the ventricles contract, the papillary muscles also contract, pulling on the chordae tendineae. This keeps the leaflets of the mitral and tricuspid valves from being pushed into the atria by high ventricular pressure.
What happens to the SA node's firing rate during sympathetic stimulation (Norepinephrine)?
- A Decrease in sodium funny current
- B Decrease in the threshold potential
- C Steeper Phase 4 depolarization slope
- D Increase in potassium efflux
Correct answer: Steeper Phase 4 depolarization slope
Norepinephrine increases the inward flow of sodium and calcium. This steeper slope of the pacemaker potential means the threshold is reached faster, increasing the heart rate (positive chronotropy).
The epicardium of the heart is also known as the:
- A Parietal pericardium
- B Visceral pericardium
- C Endocardium
- D Fibrous pericardium
Correct answer: Visceral pericardium
The epicardium is the outermost layer of the heart wall and is histologically the same as the visceral layer of the serous pericardium. It provides a smooth, slippery surface for the heart's movement.
Which cardiac chamber has the thickest muscular wall?
- A Right Atrium
- B Left Atrium
- C Right Ventricle
- D Left Ventricle
Correct answer: Left Ventricle
The left ventricle must generate enough pressure to pump blood through the entire systemic circulation. To overcome high systemic resistance, it has significantly more myocardium than the other chambers.
Gap junctions in intercalated discs are essential for heart function because they:
- A Anchor actin filaments to the cell membrane
- B Let the heart act as a functional syncytium
- C Prevent overstretching of the cardiac fibers
- D Store calcium for muscle contraction
Correct answer: Let the heart act as a functional syncytium
Gap junctions provide low-resistance electrical connections between adjacent cardiac cells. This allows action potentials to spread rapidly from cell to cell, so the entire chamber contracts as a single coordinated unit.
Which of the following is true regarding the 'Absolute Refractory Period' of cardiac muscle?
- A It is much shorter than in skeletal muscle
- B It lasts almost as long as the whole contraction
- C It allows the heart to reach a state of tetanus
- D It occurs during Phase 4 of the action potential
Correct answer: It lasts almost as long as the whole contraction
The absolute refractory period in cardiac muscle is very long (about 250ms), lasting through the plateau of the action potential. This prevents the heart from being re-excited until it has relaxed, preventing sustained (tetanic) contractions.
The coronary sinus receives deoxygenated blood from the coronary veins and empties directly into the:
- A Left Atrium
- B Superior Vena Cava
- C Right Atrium
- D Pulmonary Artery
Correct answer: Right Atrium
The coronary sinus is the primary vein of the heart. It collects blood from the myocardium and returns it to the right atrium alongside the superior and inferior vena cavae.
Which lead on a standard 12-lead ECG is most directly associated with looking at the electrical activity of the SA node?
- A Lead I
- B Lead II
- C aVR
- D V6
Correct answer: Lead II
Lead II follows the natural axis of the heart's depolarization (from the right shoulder to the left leg). Because it aligns with the path from the SA node to the ventricles, it typically shows the clearest P waves.
The term 'dromotropy' refers specifically to which property of the heart?
- A Heart rate
- B Contractility
- C Conduction speed
- D Excitability
Correct answer: Conduction speed
Dromotropy relates to the speed of conduction of electrical impulses, particularly through the AV node. Factors that increase conduction speed are said to have a positive dromotropic effect.