Electrophysiology MCQs With Answer

Master electrophysiology fundamentals with targeted, exam-focused content ideal for B.Pharm students. This collection of Electrophysiology MCQs With Answer covers cardiac and neuronal action potentials, ion channels (Na+, K+, Ca2+), resting membrane potential, ECG interpretation, antiarrhythmic pharmacology, and experimental techniques like patch-clamp and intracardiac studies. Each question emphasizes clinical relevance, drug mechanisms, and quantitative concepts such as Nernst and Goldman equations to strengthen your pharmacological reasoning. Questions range from basic membrane physiology to advanced arrhythmia mechanisms and drug effects, helping you build strong recall and application skills for exams and practical pharmacy tasks. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What primary ionic movement accounts for the rapid upstroke (phase 0) of the ventricular action potential?

• Influx of calcium through L-type Ca2+ channels
• Efflux of potassium through delayed rectifier K+ channels
• Influx of sodium through fast voltage-gated Na+ channels
• Influx of chloride through GABA-gated channels

Correct Answer: Influx of sodium through fast voltage-gated Na+ channels

Q2. Which equation is used to calculate the equilibrium potential for a single ion species?

• Goldman-Hodgkin-Katz equation
• Nernst equation
• Henderson-Hasselbalch equation
• Michaelis-Menten equation

Correct Answer: Nernst equation

Q3. The resting membrane potential of most neurons is closest to which ion’s equilibrium potential and why?

• Sodium, because cells have high Na+ permeability at rest
• Chloride, because Cl- is actively transported into the cell
• Potassium, because resting membrane permeability is highest for K+
• Calcium, because intracellular Ca2+ concentration is high

Correct Answer: Potassium, because resting membrane permeability is highest for K+

Q4. Which of the following best describes the Goldman equation?

• Calculates membrane potential using concentration gradients of a single ion
• Estimates membrane potential considering multiple ions and their permeabilities
• Predicts enzyme kinetics in ion transporters
• Measures ionic currents in a patch-clamp experiment

Correct Answer: Estimates membrane potential considering multiple ions and their permeabilities

Q5. Which current is primarily responsible for pacemaker depolarization (phase 4) in sinoatrial node cells?

• Fast sodium current (INa)
• Funny current (If) carried by HCN channels
• Delayed rectifier potassium current (IK)
• Calcium-activated chloride current

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

Q6. Patch-clamp electrophysiology is mainly used to:

• Measure blood ion concentrations in vivo
• Record ionic currents through individual ion channels or whole cells
• Visualize cardiac conduction pathways macroscopically
• Detect antibody-mediated ion channelopathies only

Correct Answer: Record ionic currents through individual ion channels or whole cells

Q7. A drug that blocks L-type calcium channels will most directly affect which cardiac property?

• Phase 0 slope in ventricular myocytes
• Plateau phase (phase 2) and contractility
• Resting membrane potential of skeletal muscle
• Fast sodium channel availability in Purkinje fibers

Correct Answer: Plateau phase (phase 2) and contractility

Q8. The best description of an action potential refractory period is:

• Time when membrane potential is at rest and can fire repeatedly with no limit
• Interval when a second action potential cannot be initiated or requires larger stimulus
• Phase when ion channels are permanently inactivated
• Period during which only calcium channels are active

Correct Answer: Interval when a second action potential cannot be initiated or requires larger stimulus

Q9. Which antiarrhythmic class primarily blocks fast sodium channels and slows conduction velocity?

• Class II (beta-blockers)
• Class I (sodium channel blockers)
• Class IV (calcium channel blockers)
• Class III (potassium channel blockers)

Correct Answer: Class I (sodium channel blockers)

Q10. Which change is most likely to produce prolongation of the QT interval and risk torsades de pointes?

• Blockade of inward sodium current only
• Enhanced funny current in SA node
• Blockade of delayed rectifier potassium current (IKr)
• Increased gap junction conductance

Correct Answer: Blockade of delayed rectifier potassium current (IKr)

Q11. In ventricular myocytes, what is the main ionic basis for repolarization during phase 3?

• Activation of L-type calcium channels
• Activation of inward rectifier potassium channels only
• Increased outward potassium currents through delayed rectifiers
• Increased sodium influx through persistent channels

Correct Answer: Increased outward potassium currents through delayed rectifiers

Q12. Which laboratory technique allows direct measurement of single-channel conductance?

• Electrocardiography (ECG)
• Patch-clamp recording in single-channel mode
• Western blotting for channel proteins
• Optical coherence tomography

Correct Answer: Patch-clamp recording in single-channel mode

Q13. Which cardiac tissue normally has the slowest conduction velocity?

• Purkinje fibers
• Atrial myocardium
• Ventricular myocardium
• Atrioventricular (AV) node

Correct Answer: Atrioventricular (AV) node

Q14. Delayed afterdepolarizations (DADs) are commonly associated with which underlying mechanism?

• Excess intracellular calcium leading to spontaneous SR release
• Prolonged action potential due to K+ channel block
• Reduced funny current in pacemaker cells
• Increased chloride conductance at rest

Correct Answer: Excess intracellular calcium leading to spontaneous SR release

Q15. Which ion channel is the primary target of class IV antiarrhythmic drugs?

• Voltage-gated sodium channels
• Delayed rectifier potassium channels
• L-type calcium channels
• HCN channels (funny current)

Correct Answer: L-type calcium channels

Q16. The slope of phase 4 depolarization determines:

• Conduction velocity through Purkinje fibers only
• Action potential amplitude in ventricular myocytes
• Spontaneous firing rate of pacemaker cells
• Duration of the absolute refractory period

Correct Answer: Spontaneous firing rate of pacemaker cells

Q17. Which parameter does the time constant (tau) of a membrane describe?

• Distance over which potential decays in tissue
• How quickly membrane potential responds to a current step
• Maximal AP amplitude
• Equilibrium potential for K+

Correct Answer: How quickly membrane potential responds to a current step

Q18. In the context of electrophysiology, the space constant (lambda) indicates:

• The time required for channel recovery from inactivation
• How far an electrical signal passively spreads along a fiber
• The energy needed to open a voltage-gated channel
• The refractory period duration

Correct Answer: How far an electrical signal passively spreads along a fiber

Q19. A decrease in extracellular potassium concentration (hypokalemia) typically causes:

• Membrane depolarization and increased excitability
• Membrane hyperpolarization and decreased excitability
• No change in resting potential
• Immediate cell lysis

Correct Answer: Membrane hyperpolarization and decreased excitability

Q20. Which antiarrhythmic drug is a class III agent that prolongs action potential duration by blocking K+ channels?

• Propranolol
• Amiodarone
• Lidocaine
• Verapamil

Correct Answer: Amiodarone

Q21. The effective refractory period (ERP) is most closely related to:

• The time a membrane potential is above threshold only
• The interval during which a premature impulse cannot produce a propagated AP
• The duration between two heartbeats measured on ECG
• The maximal diastolic potential in pacemaker cells

Correct Answer: The interval during which a premature impulse cannot produce a propagated AP

Q22. In neurons, tetrodotoxin (TTX) blocks which channels?

• Voltage-gated calcium channels
• Voltage-gated sodium channels
• Voltage-gated potassium channels
• Ligand-gated chloride channels

Correct Answer: Voltage-gated sodium channels

Q23. Which ECG change corresponds to ventricular depolarization?

• P wave
• QRS complex
• T wave
• U wave

Correct Answer: QRS complex

Q24. Early afterdepolarizations (EADs) are favored by:

• Shortened action potential duration
• Drugs that excessively prolong action potential duration
• Complete absence of calcium currents
• Increased gap junction conductance only

Correct Answer: Drugs that excessively prolong action potential duration

Q25. Which statement about gap junctions in cardiac tissue is correct?

• They are chemical synapses using neurotransmitters
• They electrically couple myocytes allowing direct ionic flow
• They prevent spread of action potentials between cells
• They are made primarily of collagen fibers

Correct Answer: They electrically couple myocytes allowing direct ionic flow

Q26. The safety factor for conduction in cardiac tissue refers to:

• The ratio of inward to outward current during an action potential upstroke ensuring propagation
• The number of ion channels expressed per cell
• The threshold potential only
• The time between depolarization and repolarization

Correct Answer: The ratio of inward to outward current during an action potential upstroke ensuring propagation

Q27. Which mechanism explains how class Ib antiarrhythmics (e.g., lidocaine) preferentially affect ischemic tissue?

• They target HCN channels present only in ischemic tissue
• They bind more avidly to inactivated sodium channels prevalent in depolarized ischemic cells
• They increase extracellular potassium selectively in ischemic regions
• They open gap junctions to restore conduction

Correct Answer: They bind more avidly to inactivated sodium channels prevalent in depolarized ischemic cells

Q28. Which ion’s intracellular accumulation is most associated with increased contractility in cardiac myocytes?

• Sodium
• Calcium
• Chloride
• Magnesium

Correct Answer: Calcium

Q29. Which statement about the action potential of SA nodal cells is true?

• They have a stable resting membrane potential maintained by inward rectifier K+ channels
• Phase 0 is mediated by fast sodium channels as in ventricular myocytes
• They lack a true resting potential and exhibit spontaneous depolarization
• They have no calcium influx during the action potential

Correct Answer: They lack a true resting potential and exhibit spontaneous depolarization

Q30. Which laboratory measurement primarily reflects atrial depolarization?

• T wave amplitude
• PR interval
• P wave
• ST segment elevation

Correct Answer: P wave

Q31. Which drug class reduces heart rate by blocking beta-adrenergic receptors?

• Class I antiarrhythmics
• Class II antiarrhythmics
• Class III antiarrhythmics
• Class IV antiarrhythmics

Correct Answer: Class II antiarrhythmics

Q32. In electrophysiology, an electrotonic potential refers to:

• An action potential with full amplitude and regeneration
• A passive, graded change in membrane potential that decays with time and distance
• A synaptic potential that triggers neurotransmitter release
• A measurement artifact only seen in patch-clamp

Correct Answer: A passive, graded change in membrane potential that decays with time and distance

Q33. Which ion channel dysfunction is classically associated with congenital long QT syndrome?

• Loss-of-function in specific potassium channels like IKr
• Gain-of-function in chloride channels only
• Enhanced gap junction communication
• Overexpression of HCN channels in ventricles

Correct Answer: Loss-of-function in specific potassium channels like IKr

Q34. Which effect would an acetylcholine-sensitive potassium current (IK,ACh) have on heart rate?

• Increase heart rate by depolarizing SA node cells
• Decrease heart rate by hyperpolarizing pacemaker cells
• No effect on heart rate
• Only affects ventricular contractility

Correct Answer: Decrease heart rate by hyperpolarizing pacemaker cells

Q35. In an action potential, the “plateau” phase in ventricular myocytes is due to a balance between:

• Fast Na+ influx and K+ efflux
• Slow Ca2+ influx and outward K+ currents
• Chloride influx and sodium efflux
• HCN current and inward rectifier K+ only

Correct Answer: Slow Ca2+ influx and outward K+ currents

Q36. Which measurement technique is noninvasive and provides a surface recording of cardiac electrical activity?

• Intracardiac electrogram
• Electrocardiography (ECG)
• Patch-clamp of single myocytes
• Endomyocardial biopsy

Correct Answer: Electrocardiography (ECG)

Q37. Which ion exchanger contributes to removing intracellular calcium after a cardiac contraction?

• Sodium-calcium exchanger (NCX)
• Potassium-chloride cotransporter
• Proton pump
• Glucose transporter

Correct Answer: Sodium-calcium exchanger (NCX)

Q38. Which of the following is an example of a use-dependent sodium channel blocker?

• Propranolol
• Lidocaine
• Amiodarone
• Verapamil

Correct Answer: Lidocaine

Q39. Which technique is used clinically to map arrhythmic foci and guide catheter ablation?

• Surface electromyography
• Intracardiac electrophysiology study with mapping
• Coronary angiography
• Cardiac MRI only

Correct Answer: Intracardiac electrophysiology study with mapping

Q40. Which ionic current contributes to the maintenance of resting membrane potential in ventricular myocytes?

• Persistent inward sodium current only
• Inward rectifier potassium current (IK1)
• L-type calcium current
• HCN-mediated funny current

Correct Answer: Inward rectifier potassium current (IK1)

Q41. Which clinical effect is associated with digitalis (digoxin) related to electrophysiology?

• Decrease intracellular calcium and negative inotropy
• Increase vagal tone and slow AV nodal conduction
• Block fast sodium channels causing broad QRS
• Selective HCN channel blockade increasing heart rate

Correct Answer: Increase vagal tone and slow AV nodal conduction

Q42. Which ion channel opening would most rapidly hyperpolarize a neuron?

• Opening of voltage-gated sodium channels
• Opening of potassium channels increasing K+ efflux
• Opening of L-type calcium channels
• Opening of nonselective cation channels

Correct Answer: Opening of potassium channels increasing K+ efflux

Q43. Which property allows some antiarrhythmic drugs to preferentially affect rapidly firing cells?

• State-dependent binding to inactivated channels (use-dependence)
• Binding only to closed channels at very negative potentials
• Complete selectivity for skeletal muscle channels
• Only affecting ligand-gated receptors

Correct Answer: State-dependent binding to inactivated channels (use-dependence)

Q44. In cardiac electrophysiology, what does the PR interval represent?

• Time from atrial depolarization to ventricular depolarization, reflecting AV conduction
• Ventricular repolarization time
• Duration of ventricular systole
• Intrinsic sinus rate measured in seconds

Correct Answer: Time from atrial depolarization to ventricular depolarization, reflecting AV conduction

Q45. Which electrolyte disturbance commonly predisposes to digitalis toxicity and arrhythmias?

• Hyperkalemia
• Hypokalemia
• Hypermagnesemia only
• Elevated intracellular chloride

Correct Answer: Hypokalemia

Q46. Which current contributes to the depolarizing phase of nodal action potentials when sodium current is minimal?

• Fast sodium current (INa)
• Slow inward calcium current (ICa,L)
• Outward potassium current only
• GABA-mediated chloride current

Correct Answer: Slow inward calcium current (ICa,L)

Q47. Which pharmacologic action would likely slow atrioventricular nodal conduction most directly?

• Blockade of L-type calcium channels
• Blockade of delayed rectifier potassium channels in ventricles only
• Activation of HCN channels in ventricles
• Opening sodium channels in atrial myocytes

Correct Answer: Blockade of L-type calcium channels

Q48. Which clinical sign on ECG suggests increased vagal tone affecting the heart?

• Shortened PR interval
• Sinus bradycardia with prolonged PR interval
• Widened QRS complex without rate change
• ST-segment elevation in leads II, III, aVF only

Correct Answer: Sinus bradycardia with prolonged PR interval

Q49. Which of the following best characterizes the mechanism of action of class Ia antiarrhythmic drugs?

• Potent beta-adrenergic blockade with no effect on ion channels
• Sodium channel blockade with intermediate kinetics and prolongation of repolarization
• Pure potassium channel blockade without sodium effects
• Selective HCN channel agonism

Correct Answer: Sodium channel blockade with intermediate kinetics and prolongation of repolarization

Q50. Which process is essential for the rapid termination of a synaptic signal in neuronal electrophysiology?

• Pump-mediated removal of neurotransmitter only from the synaptic vesicle
• Reuptake and enzymatic degradation of neurotransmitter in the synaptic cleft
• Permanent binding of neurotransmitter to receptors
• Continual calcium influx to maintain the signal indefinitely

Correct Answer: Reuptake and enzymatic degradation of neurotransmitter in the synaptic cleft

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.

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