Heart beat and its regulation by autonomic nervous system MCQs With Answer

Introduction: The heart beat and its regulation by the autonomic nervous system is a core topic for B. Pharm students, linking physiology and pharmacology. This introduction covers pacemaker function of the SAN and AVN, autonomic inputs (sympathetic and parasympathetic), key receptors such as beta-1 and muscarinic M2, ionic currents (funny current, L-type Ca2+), and clinical drug targets like beta-blockers, ivabradine and atropine. Understanding chronotropy, dromotropy, inotropy and reflexes (baroreceptor-mediated) is essential for rational drug use and predicting adverse effects. Emphasis is on mechanisms, signalling pathways and therapeutic implications relevant to pharmacy practice. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the primary pacemaker of the heart?

• Sinoatrial node (SAN)
• Atrioventricular node (AVN)
• Bundle of His
• Purkinje fibers

Correct Answer: Sinoatrial node (SAN)

Q2. Which ionic current is most responsible for the spontaneous depolarization (phase 4) in SAN pacemaker cells?

• Delayed rectifier potassium current (IK)
• Funny current (If) carried by HCN channels
• L-type calcium current (ICa,L)
• Sodium fast inward current (INa)

Correct Answer: Funny current (If) carried by HCN channels

Q3. Sympathetic stimulation increases heart rate primarily by which mechanism?

• Activation of muscarinic M2 receptors increasing GIRK channels
• Activation of beta-1 receptors increasing cAMP and If/ICa,L
• Blocking L-type calcium channels
• Increasing vagal tone to the SAN

Correct Answer: Activation of beta-1 receptors increasing cAMP and If/ICa,L

Q4. Parasympathetic (vagal) activation slows the heart by:

• Increasing intracellular cAMP in pacemaker cells
• Opening G-protein gated inwardly rectifying K+ (GIRK) channels and reducing cAMP
• Stimulating beta-1 mediated PKA phosphorylation of Ca channels
• Enhancing RyR2-mediated Ca2+ release

Correct Answer: Opening G-protein gated inwardly rectifying K+ (GIRK) channels and reducing cAMP

Q5. Which receptor subtype mediates parasympathetic effects on heart rate?

• Beta-2 adrenergic receptor
• Alpha-1 adrenergic receptor
• Muscarinic M2 receptor
• Nicotine N1 receptor

Correct Answer: Muscarinic M2 receptor

Q6. Beta-1 receptor activation in cardiomyocytes primarily couples to which G protein and second messenger?

• Gi protein and decreased cAMP
• Gs protein and increased cAMP
• Gq protein and increased IP3/DAG
• G12/13 protein and Rho activation

Correct Answer: Gs protein and increased cAMP

Q7. Ivabradine lowers heart rate by selectively inhibiting which target?

• L-type Ca2+ channels
• Beta-1 adrenergic receptors
• HCN (funny) channels responsible for If
• Muscarinic M2 receptors

Correct Answer: HCN (funny) channels responsible for If

Q8. Which effect is NOT typically produced by sympathetic stimulation of the heart?

• Increased heart rate (positive chronotropy)
• Increased AV nodal conduction (positive dromotropy)
• Decreased myocardial contractility (negative inotropy)
• Enhanced relaxation via phospholamban phosphorylation (positive lusitropy)

Correct Answer: Decreased myocardial contractility (negative inotropy)

Q9. Baroreceptor reflex response to an acute increase in blood pressure involves:

• Decreased baroreceptor firing, increased sympathetic outflow
• Increased baroreceptor firing, increased vagal outflow, reduced HR
• Direct activation of beta-1 receptors on SAN by high pressure
• Activation of peripheral chemoreceptors raising HR

Correct Answer: Increased baroreceptor firing, increased vagal outflow, reduced HR

Q10. Digoxin can slow ventricular rate in atrial fibrillation mainly by:

• Blocking beta receptors in the AV node
• Enhancing vagal tone and reducing AV nodal conduction
• Direct blockade of HCN channels at the SAN
• Increasing sympathetic outflow to override atrial impulses

Correct Answer: Enhancing vagal tone and reducing AV nodal conduction

Q11. The intrinsic heart rate (without autonomic influence) is approximately:

• 40 bpm
• 60 bpm
• 100 bpm
• 140 bpm

Correct Answer: 100 bpm

Q12. Which ion channel blockade would most directly reduce AV nodal conduction velocity?

• Block of fast sodium channels (INa)
• Block of L-type calcium channels (ICa,L)
• Block of HCN channels (If)
• Block of delayed rectifier K+ channels (IK)

Correct Answer: Block of L-type calcium channels (ICa,L)

Q13. Which pharmacologic agent would increase heart rate by antagonizing parasympathetic activity?

• Propranolol
• Atropine
• Carvedilol
• Ivabradine

Correct Answer: Atropine

Q14. Activation of cardiac muscarinic M2 receptors primarily results in:

• Increased cAMP and enhanced Ca2+ entry
• Opening of GIRK channels causing hyperpolarization
• Activation of phospholipase C and IP3 production
• Inhibition of K+ conductance

Correct Answer: Opening of GIRK channels causing hyperpolarization

Q15. Which statement about the atrioventricular (AV) node is correct?

• It has the fastest conduction velocity in the heart.
• It provides the only normal electrical connection between atria and ventricles and slows conduction.
• It is the primary site of impulse initiation in a healthy heart.
• It is insensitive to autonomic modulation.

Correct Answer: It provides the only normal electrical connection between atria and ventricles and slows conduction.

Q16. Beta-blockers reduce heart rate primarily by:

• Antagonizing beta-1 receptors to lower cAMP and reduce If/ICa,L
• Stimulating muscarinic receptors at the SAN
• Blocking K+ channels to prolong repolarization
• Enhancing HCN channel activity

Correct Answer: Antagonizing beta-1 receptors to lower cAMP and reduce If/ICa,L

Q17. Heart rate variability (HRV) is an index of autonomic control. Higher HRV generally indicates:

• Dominant sympathetic tone and worse prognosis
• Reduced autonomic modulation
• Healthy vagal-sympathetic balance and better cardiovascular adaptability
• Complete autonomic failure

Correct Answer: Healthy vagal-sympathetic balance and better cardiovascular adaptability

Q18. Which preganglionic spinal segments supply sympathetic cardiac fibers?

• Cranial nerves IX and X
• T1–T4 (thoracic) segments
• L1–L2 segments
• S2–S4 segments

Correct Answer: T1–T4 (thoracic) segments

Q19. Which drug is most likely to cause reflex tachycardia due to vasodilation?

• Propranolol
• Nitroprusside
• Ivabradine
• Atropine

Correct Answer: Nitroprusside

Q20. In SAN cells, PKA-mediated phosphorylation following beta-1 activation increases heart rate by:

• Decreasing ICa,L activity
• Enhancing opening of L-type Ca2+ channels and increasing If
• Activating muscarinic receptors
• Opening inward rectifier K+ channels (IK1)

Correct Answer: Enhancing opening of L-type Ca2+ channels and increasing If

Q21. Which autonomic intervention would increase PR interval on ECG?

• Sympathetic stimulation
• Parasympathetic (vagal) stimulation
• Beta-1 agonist administration
• Ivabradine administration

Correct Answer: Parasympathetic (vagal) stimulation

Q22. Mechanistically, how does increased intracellular cAMP speed up pacemaker activity?

• By decreasing funny current (If)
• By directly blocking L-type Ca2+ channels
• By shifting HCN channel activation to more positive potentials and enhancing Ca2+ channel opening
• By activating GIRK channels

Correct Answer: By shifting HCN channel activation to more positive potentials and enhancing Ca2+ channel opening

Q23. Which condition increases vagal tone and can produce sinus bradycardia?

• Hyperthyroidism
• During deep inspiration (respiratory sinus arrhythmia)
• Acute sympathetic surge
• Beta-1 agonist infusion

Correct Answer: During deep inspiration (respiratory sinus arrhythmia)

Q24. Which ion flux predominates during the upstroke of the action potential in SAN cells?

• Fast sodium influx (INa)
• L-type calcium influx (ICa,L)
• Potassium efflux (IK)
• Cl- influx

Correct Answer: L-type calcium influx (ICa,L)

Q25. A drug that is a selective M2 receptor agonist would most likely cause:

• Tachycardia and increased AV conduction
• Bradycardia and slowed AV conduction
• Vasoconstriction and hypertension
• Increased myocardial contractility

Correct Answer: Bradycardia and slowed AV conduction

Q26. Which physiological change explains positive lusitropy during sympathetic stimulation?

• Decreased SERCA activity due to phospholamban dephosphorylation
• Increased SERCA activity via phospholamban phosphorylation enhancing relaxation
• Inhibition of RyR2 decreasing Ca2+ release
• Opening of GIRK channels in ventricular myocytes

Correct Answer: Increased SERCA activity via phospholamban phosphorylation enhancing relaxation

Q27. Which statement about autonomic innervation of the heart is TRUE?

• Parasympathetic fibers increase ventricular contractility strongly
• Sympathetic fibers originate from the sacral spinal cord
• Vagus nerve provides parasympathetic innervation mainly to SAN and AVN
• Autonomic nerves do not influence pacemaker cells

Correct Answer: Vagus nerve provides parasympathetic innervation mainly to SAN and AVN

Q28. In treating supraventricular tachycardia due to AV nodal reentry, which agent is commonly used to transiently block AV nodal conduction?

• Adenosine
• Isoproterenol
• Dobutamine
• Propranolol in high dose

Correct Answer: Adenosine

Q29. Which laboratory measure is most directly affected by autonomic regulation of heart rate?

• Serum troponin concentration
• QT interval independent of HR
• R-R interval variability on ECG (HRV)
• Serum potassium concentration

Correct Answer: R-R interval variability on ECG (HRV)

Q30. Which clinical effect would you expect from an acute overdose of a nonselective beta-blocker like propranolol?

• Marked tachycardia and hypertension
• Bradycardia, decreased AV conduction, and potential bronchoconstriction
• Excessive vagal stimulation causing diarrhea
• Selective vasodilation without cardiac effects

Correct Answer: Bradycardia, decreased AV conduction, and potential bronchoconstriction

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com