Action potential MCQs With Answer

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Action potential MCQs With Answer are essential study tools for B. Pharm students to master neuronal and cardiac excitability, membrane biophysics, and pharmacological modulation. This set covers mechanisms of depolarization, repolarization, refractory periods, ion channel kinetics, electrochemical gradients, and drug actions such as local anesthetics, antiarrhythmics, and ion channel blockers. Questions emphasize clinical relevance, experimental techniques (patch-clamp, Hodgkin-Huxley concepts), and comparisons between neuronal and cardiac action potentials. Focused practice with answers sharpens problem-solving for exams and therapeutics. Clear explanations of ion conductance, Nernst/Goldman principles, and pathology like demyelination are integrated into the MCQs. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What best describes the ‘all-or-none’ property of an action potential?

  • Action potentials vary in amplitude with stimulus strength
  • Action potentials occur only if threshold is reached and have a fixed amplitude
  • Action potentials gradually increase in size as depolarization continues
  • Action potentials can be stopped midway by a stronger stimulus

Correct Answer: Action potentials occur only if threshold is reached and have a fixed amplitude

Q2. Typical neuronal resting membrane potential is closest to which value?

  • +40 mV
  • 0 mV
  • -70 mV
  • -120 mV

Correct Answer: -70 mV

Q3. Which ion movement primarily causes the rapid depolarization phase of a neuronal action potential?

  • Efflux of K+
  • Influx of Na+
  • Influx of Cl-
  • Efflux of Ca2+

Correct Answer: Influx of Na+

Q4. Which phase of the action potential is mainly mediated by voltage-gated K+ channels opening?

  • Depolarization
  • Repolarization
  • Resting potential
  • Synaptic potential

Correct Answer: Repolarization

Q5. The absolute refractory period occurs because:

  • Voltage-gated Na+ channels are inactivated and cannot reopen
  • K+ channels remain permanently closed
  • Sodium concentration outside the cell is depleted

Correct Answer: Voltage-gated Na+ channels are inactivated and cannot reopen

Q6. Saltatory conduction accelerates action potential propagation by:

  • Increasing membrane capacitance along the axon
  • Reducing ion channel density at nodes
  • Allowing action potentials to jump between nodes of Ranvier
  • Converting action potentials into graded potentials

Correct Answer: Allowing action potentials to jump between nodes of Ranvier

Q7. Myelination increases conduction velocity primarily by:

  • Increasing membrane ion permeability everywhere
  • Decreasing membrane resistance
  • Reducing membrane capacitance and increasing effective resistance between nodes
  • Removing voltage-gated channels from nodes

Correct Answer: Reducing membrane capacitance and increasing effective resistance between nodes

Q8. Which equation accounts for the contributions of multiple ions and their permeabilities to membrane potential?

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

Correct Answer: Goldman-Hodgkin-Katz equation

Q9. Tetrodotoxin (TTX) blocks action potentials by:

  • Inhibiting voltage-gated K+ channels
  • Blocking voltage-gated Na+ channels from the extracellular side
  • Activating Na+/K+ ATPase
  • Blocking L-type Ca2+ channels

Correct Answer: Blocking voltage-gated Na+ channels from the extracellular side

Q10. Local anesthetics such as lidocaine reduce pain by:

  • Enhancing neurotransmitter release
  • Blocking voltage-gated Na+ channels in a use-dependent manner
  • Blocking K+ channels to prolong action potentials
  • Increasing synaptic vesicle fusion

Correct Answer: Blocking voltage-gated Na+ channels in a use-dependent manner

Q11. During the cardiac action potential, the plateau phase is primarily due to:

  • Persistent Na+ influx through fast Na+ channels
  • Inward Ca2+ current through L-type channels balanced by K+ efflux
  • Cl- influx stabilizing membrane potential
  • Activation of HCN channels

Correct Answer: Inward Ca2+ current through L-type channels balanced by K+ efflux

Q12. Which ion’s equilibrium potential most strongly determines the resting membrane potential in neurons?

  • Calcium (Ca2+)
  • Sodium (Na+)
  • Potassium (K+)
  • Chloride (Cl-)

Correct Answer: Potassium (K+)

Q13. The Na+/K+ ATPase contributes to the resting membrane potential by:

  • Directly making the membrane potential positive
  • Pumping 3 Na+ out and 2 K+ in, creating an electrogenic effect
  • Allowing passive diffusion of ions
  • Opening voltage-gated channels

Correct Answer: Pumping 3 Na+ out and 2 K+ in, creating an electrogenic effect

Q14. Which experimental technique allows measurement of single ion channel currents?

  • Western blotting
  • Patch-clamp recording
  • ELISA
  • Flow cytometry

Correct Answer: Patch-clamp recording

Q15. Hodgkin and Huxley contributed to action potential understanding by:

  • Describing ionic currents with empiric gating variables and differential equations
  • Showing that ATP directly generates action potentials
  • Proving action potentials are chemical impulses only
  • Inventing the first myelin sheath model

Correct Answer: Describing ionic currents with empiric gating variables and differential equations

Q16. Refractory periods are important clinically because they:

  • Allow two action potentials to travel in opposite directions simultaneously
  • Prevent retrograde propagation and limit maximal firing frequency
  • Increase sodium permeability indefinitely
  • Cause permanent inactivation of all ion channels

Correct Answer: Prevent retrograde propagation and limit maximal firing frequency

Q17. Hyperkalemia (elevated extracellular K+) typically affects neurons by:

  • Hyperpolarizing the membrane and reducing excitability
  • Depolarizing the membrane and potentially inactivating Na+ channels
  • Increasing the electrochemical gradient for K+ efflux
  • Blocking ligand-gated channels selectively

Correct Answer: Depolarizing the membrane and potentially inactivating Na+ channels

Q18. Which drug class acts by blocking L-type Ca2+ channels and thereby shortens the cardiac action potential plateau?

  • Beta-blockers
  • Calcium channel blockers (e.g., verapamil)
  • ACE inhibitors
  • Loop diuretics

Correct Answer: Calcium channel blockers (e.g., verapamil)

Q19. Afterhyperpolarization following an action potential is primarily mediated by:

  • Persistent Na+ current
  • Delayed K+ currents and Ca2+-activated K+ channels
  • HCN channel activation only
  • Chloride channel closure

Correct Answer: Delayed K+ currents and Ca2+-activated K+ channels

Q20. The axon hillock is important because it:

  • Is the primary site for neurotransmitter release
  • Has a high density of voltage-gated Na+ channels and often initiates spikes
  • Is where synaptic vesicles are recycled
  • Is responsible for myelination

Correct Answer: Has a high density of voltage-gated Na+ channels and often initiates spikes

Q21. A use-dependent block of Na+ channels means:

  • Drug binding is stronger when channels are closed
  • Drug preferentially binds to open or inactivated channels and blocks during high activity
  • Drug affects resting membrane potential only
  • Block increases with decreasing firing rate

Correct Answer: Drug preferentially binds to open or inactivated channels and blocks during high activity

Q22. Which ion channel type is primarily responsible for generating inhibitory postsynaptic potentials (IPSPs) in many neurons?

  • Voltage-gated Na+ channels
  • Ligand-gated Cl- channels (e.g., GABA-A) or K+ channels
  • L-type Ca2+ channels
  • HCN channels

Correct Answer: Ligand-gated Cl- channels (e.g., GABA-A) or K+ channels

Q23. Demyelinating disease such as multiple sclerosis causes conduction failure because:

  • It increases the number of nodes of Ranvier
  • It increases membrane resistance and enhances conduction
  • Loss of myelin increases capacitance and decreases membrane resistance, causing current leak
  • It converts action potentials into chemical gradients

Correct Answer: Loss of myelin increases capacitance and decreases membrane resistance, causing current leak

Q24. The Nernst equation calculates:

  • The membrane potential when multiple ions are permeable
  • The equilibrium potential for a single ion based on concentration gradient
  • The rate constant for channel opening
  • The capacitance of the membrane

Correct Answer: The equilibrium potential for a single ion based on concentration gradient

Q25. Which statement about synaptic transmission and action potential coupling is correct?

  • Action potentials directly cross the synaptic cleft to excite the next neuron
  • Presynaptic action potential triggers Ca2+ influx that initiates neurotransmitter release
  • Postsynaptic action potentials always originate at dendrites
  • Neurotransmitter release is independent of extracellular Ca2+

Correct Answer: Presynaptic action potential triggers Ca2+ influx that initiates neurotransmitter release

Q26. Which ionic current contributes to pacemaker potentials in sinoatrial node cells?

  • Fast voltage-gated Na+ current only
  • HCN-mediated funny current (If) and T-type Ca2+ currents
  • Cl- outward current
  • Outward K+ leak exclusively

Correct Answer: HCN-mediated funny current (If) and T-type Ca2+ currents

Q27. Length constant (lambda) in cable theory refers to:

  • The distance along the membrane where voltage decays to ~37% of its original value
  • The time taken for the membrane potential to change by 63%
  • The axonal diameter in micrometers
  • The frequency of action potential firing

Correct Answer: The distance along the membrane where voltage decays to ~37% of its original value

Q28. Time constant (tau) is defined as:

  • Membrane resistance divided by membrane capacitance
  • Membrane capacitance times membrane resistance indicating how quickly voltage changes
  • The inverse of conduction velocity
  • The refractory period duration

Correct Answer: Membrane capacitance times membrane resistance indicating how quickly voltage changes

Q29. Which of the following increases conduction velocity in unmyelinated axons?

  • Decreasing axon diameter
  • Increasing axon diameter to reduce internal resistance
  • Adding more leak channels along the membrane
  • Reducing extracellular Na+ concentration

Correct Answer: Increasing axon diameter to reduce internal resistance

Q30. Use of tetraethylammonium (TEA) in experiments primarily blocks which channels?

  • Voltage-gated Na+ channels
  • Voltage-gated K+ channels
  • Ligand-gated GABA receptors
  • HCN channels

Correct Answer: Voltage-gated K+ channels

Q31. Persistent sodium current contributes to neuronal excitability by:

  • Causing a slowly inactivating inward Na+ current that can facilitate repetitive firing
  • Rapidly repolarizing the action potential
  • Blocking neurotransmitter release
  • Only operating during absolute refractory period

Correct Answer: Causing a slowly inactivating inward Na+ current that can facilitate repetitive firing

Q32. Which property allows voltage-gated channels to distinguish between open, closed and inactivated states?

  • Ion selectivity filter only
  • Gating mechanisms and state-dependent conformational changes
  • Fixed pore size unaffected by voltage
  • Membrane capacitance

Correct Answer: Gating mechanisms and state-dependent conformational changes

Q33. Frequency coding of stimulus intensity in neurons refers to:

  • Stronger stimuli produce larger amplitude action potentials
  • Stronger stimuli increase the firing rate of action potentials
  • Stimuli change the ion composition of the extracellular space permanently
  • Stronger stimuli shorten action potential duration only

Correct Answer: Stronger stimuli increase the firing rate of action potentials

Q34. Accommodation in neurons is best described as:

  • Increased excitability following rapid depolarization
  • Failure to fire in response to a slowly developing depolarization due to threshold adaptation
  • Permanent inactivation of potassium channels
  • Enhancement of synaptic transmission

Correct Answer: Failure to fire in response to a slowly developing depolarization due to threshold adaptation

Q35. Which ion has the largest difference between intracellular and extracellular concentration in typical neurons?

  • Sodium (Na+)
  • Chloride (Cl-)
  • Potassium (K+)
  • Calcium (Ca2+)

Correct Answer: Calcium (Ca2+)

Q36. Reversal potential for an ion is defined as:

  • The membrane potential at which there is no net flow of that ion across the membrane
  • The threshold for action potential initiation
  • The resting membrane potential multiplied by ion charge
  • The potential at which the cell dies

Correct Answer: The membrane potential at which there is no net flow of that ion across the membrane

Q37. Which statement about ligand-gated versus voltage-gated ion channels is true?

  • Ligand-gated channels open in response to changes in membrane voltage only
  • Voltage-gated channels open in response to specific neurotransmitters
  • Ligand-gated channels mediate fast synaptic potentials, while voltage-gated channels mediate action potential propagation
  • Both types are identical in structure and function

Correct Answer: Ligand-gated channels mediate fast synaptic potentials, while voltage-gated channels mediate action potential propagation

Q38. Spike initiation zone in most neurons is located at:

  • Distal dendrites
  • Axon hillock/initial segment
  • Presynaptic terminal
  • Soma nucleus

Correct Answer: Axon hillock/initial segment

Q39. Which anti-epileptic drug acts primarily by stabilizing the inactivated state of voltage-gated Na+ channels?

  • Phenytoin
  • Acetaminophen
  • Propranolol
  • Furosemide

Correct Answer: Phenytoin

Q40. Residual calcium in presynaptic terminals after an action potential contributes to:

  • Synaptic depression only
  • Synaptic facilitation and increased transmitter release on subsequent stimuli
  • Immediate inactivation of all Ca2+ channels
  • Reduction of vesicle docking proteins permanently

Correct Answer: Synaptic facilitation and increased transmitter release on subsequent stimuli

Q41. In voltage clamp experiments, clamping the membrane potential allows investigators to:

  • Measure ionic currents at fixed membrane potentials
  • Record natural action potential waveforms only
  • Eliminate all ion channel activity
  • Change ionic concentrations inside the pipette to match extracellular fluid only

Correct Answer: Measure ionic currents at fixed membrane potentials

Q42. The safety factor for conduction refers to:

  • The ratio of current available to bring the next segment to threshold relative to minimum required
  • The maximum firing frequency of a neuron
  • The minimal number of ion channels needed for life
  • The electrical resistance of the myelin sheath

Correct Answer: The ratio of current available to bring the next segment to threshold relative to minimum required

Q43. Which of the following is TRUE regarding cardiac versus neuronal action potentials?

  • Cardiac myocytes have a prominent plateau phase due to Ca2+ influx; many neurons do not
  • Neuronal action potentials always have a longer duration than cardiac ones
  • Both cells use the same ion channel types identically
  • Cardiac action potentials are independent of extracellular calcium

Correct Answer: Cardiac myocytes have a prominent plateau phase due to Ca2+ influx; many neurons do not

Q44. Which factor does NOT increase action potential conduction velocity?

  • Increasing axon diameter
  • Myelination
  • Lowering membrane capacitance
  • Increasing membrane leak conductance

Correct Answer: Increasing membrane leak conductance

Q45. The Goldman equation differs from the Nernst equation because it:

  • Applies only to calcium ions
  • Accounts for multiple ion species and their relative permeabilities simultaneously
  • Is only valid at absolute zero temperature
  • Neglects ion permeability entirely

Correct Answer: Accounts for multiple ion species and their relative permeabilities simultaneously

Q46. Which ion channel blocker would be expected to prolong the duration of an action potential?

  • Sodium channel blocker
  • Potassium channel blocker
  • HCN channel blocker
  • Ligand-gated chloride channel opener

Correct Answer: Potassium channel blocker

Q47. In ischemia (oxygen deprivation), neuronal action potential generation fails primarily because:

  • ATP-dependent pumps fail, disrupting ionic gradients
  • Ion channels become permanently open to Ca2+ only
  • Membrane capacitance increases dramatically
  • Membrane proteins become supercharged

Correct Answer: ATP-dependent pumps fail, disrupting ionic gradients

Q48. The term ‘reversal potential’ for synaptic current means:

  • The potential at which synaptic current changes direction (no net synaptic current)
  • The threshold for action potential initiation at synapse
  • The potential at which neurotransmitter is degraded
  • The resting membrane potential plus 10 mV

Correct Answer: The potential at which synaptic current changes direction (no net synaptic current)

Q49. Which physiological change would increase the amplitude of an excitatory postsynaptic potential (EPSP)?

  • Decreasing postsynaptic receptor number
  • Increasing extracellular Ca2+ to enhance neurotransmitter release
  • Opening more postsynaptic Cl- channels
  • Increasing action potential threshold

Correct Answer: Increasing extracellular Ca2+ to enhance neurotransmitter release

Q50. For B. Pharm students, which rationale best explains targeting ion channels in drug design?

  • Ion channels are inaccessible to small molecules and thus avoided
  • Ion channels directly control excitability, so modulators can treat arrhythmias, pain, epilepsy and neuropsychiatric conditions
  • Ion channels have no role in disease and are only structural
  • Ion channels cannot be selectively targeted

Correct Answer: Ion channels directly control excitability, so modulators can treat arrhythmias, pain, epilepsy and neuropsychiatric conditions

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