Properties of nerve fibres MCQs With Answer

Properties of nerve fibres MCQs With Answer is a concise, exam-focused guide for B. Pharm students exploring nerve fibre physiology and pharmacology. This introduction highlights key properties such as conduction velocity, diameter, myelination, saltatory conduction, refractory periods, length and time constants, ion channel behavior, and the pharmacologic modulation by local anesthetics and toxins. Understanding classification of A, B, and C fibers, determinants of excitability, and clinical implications like demyelination and conduction block is essential for therapeutics, toxicology, and neuropharmacology. The MCQs emphasize conceptual depth and drug interactions with nerve membranes to strengthen applied knowledge. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What primarily determines the conduction velocity of a nerve fibre?

• Membrane capacitance only
• Axonal diameter and myelination
• External potassium concentration only
• Number of synapses

Correct Answer: Axonal diameter and myelination

Q2. Which classification describes small, unmyelinated fibres that conduct slow pain and temperature?

• Aα fibres
• B fibres
• C fibres
• Aβ fibres

Correct Answer: C fibres

Q3. Which feature best explains saltatory conduction?

• Continuous depolarization along the axolemma
• Action potentials generated only at nodes of Ranvier
• Uniform distribution of voltage-gated Na+ channels
• Higher intracellular calcium at internodes

Correct Answer: Action potentials generated only at nodes of Ranvier

Q4. The space constant (length constant, λ) describes:

• The distance an action potential travels without decrement
• How far passive voltage spreads before falling to 37% of its original value
• The time to reach threshold from resting potential
• The refractory period duration

Correct Answer: How far passive voltage spreads before falling to 37% of its original value

Q5. Myelination affects membrane capacitance and resistance by:

• Increasing capacitance and decreasing resistance
• Decreasing capacitance and increasing membrane resistance
• No effect on capacitance but decreases resistance
• Increasing both capacitance and resistance

Correct Answer: Decreasing capacitance and increasing membrane resistance

Q6. Which ion channel inactivation state is primarily responsible for the absolute refractory period?

• Potassium channel activation
• Sodium channel closed-resting state
• Sodium channel inactivated state
• Calcium channel inactivated state

Correct Answer: Sodium channel inactivated state

Q7. Which nerve fibre type has the highest conduction velocity?

• Aδ fibres
• Aα fibres
• B fibres
• C fibres

Correct Answer: Aα fibres

Q8. Local anesthetics primarily exert their effect by:

• Blocking voltage-gated K+ channels extracellularly
• Blocking voltage-gated Na+ channels from inside the axon
• Enhancing GABAergic inhibition at synapses
• Depleting presynaptic calcium stores

Correct Answer: Blocking voltage-gated Na+ channels from inside the axon

Q9. Which property makes small myelinated fibres (B fibres) more susceptible to local anaesthetic blockade than large myelinated fibres?

• Lower metabolic activity
• Greater distance between nodes of Ranvier
• Smaller diameter leading to higher surface-to-volume ratio
• Higher resting membrane potential

Correct Answer: Smaller diameter leading to higher surface-to-volume ratio

Q10. Which toxin is known to block voltage-gated Na+ channels extracellularly and abolish action potentials?

• Ouabain
• Tetrodotoxin (TTX)
• Strychnine
• Botulinum toxin

Correct Answer: Tetrodotoxin (TTX)

Q11. The time constant (τ) of a nerve membrane equals:

• Membrane resistance divided by membrane capacitance (Rm/Cm)
• Membrane capacitance times membrane resistance (Rm × Cm)
• Length constant squared divided by conduction velocity
• The refractory period duration

Correct Answer: Membrane capacitance times membrane resistance (Rm × Cm)

Q12. Which statement about nodes of Ranvier is correct?

• They have low density of voltage-gated Na+ channels
• They are the primary sites of action potential regeneration
• They are covered by myelin produced by Schwann cells
• They decrease the efficiency of conduction

Correct Answer: They are the primary sites of action potential regeneration

Q13. Relative refractory period corresponds to:

• Complete inability to generate an action potential
• Reduced excitability where larger than normal stimulus can elicit an action potential
• Time when membrane potential is at resting level
• Interval of hyperexcitability requiring no stimulus

Correct Answer: Reduced excitability where larger than normal stimulus can elicit an action potential

Q14. Which factor decreases conduction velocity in a myelinated fibre?

• Increased axon diameter
• Reduced internodal length due to demyelination
• Higher density of Na+ channels at nodes
• Decreased membrane capacitance

Correct Answer: Reduced internodal length due to demyelination

Q15. Compound action potentials (CAPs) recorded from peripheral nerve reflect:

• Single-fibre membrane potential only
• Summed electrical activity of many fibres with different conduction velocities
• Only the fastest conducting fibres
• Only synaptic potentials

Correct Answer: Summed electrical activity of many fibres with different conduction velocities

Q16. Which Nav channel isoform is highly expressed at CNS nodes and critical for saltatory conduction?

• Nav1.1
• Nav1.6
• Nav1.8
• Nav2.0

Correct Answer: Nav1.6

Q17. How does myelination improve energy efficiency of action potential propagation?

• By increasing the number of action potentials per distance
• By reducing ionic leak and limiting active ion pumping to nodes
• By increasing continuous ion flux along the axon
• By elevating intracellular ATP consumption uniformly

Correct Answer: By reducing ionic leak and limiting active ion pumping to nodes

Q18. Which change is expected in multiple sclerosis (a demyelinating disease)?

• Increased conduction velocity in affected fibres
• Decreased safety factor and conduction block
• Greater internodal resistance improving conduction
• Enhanced saltatory conduction

Correct Answer: Decreased safety factor and conduction block

Q19. Which of the following best describes “safety factor” for conduction?

• The ratio of available Na+ channels to K+ channels
• The margin by which depolarizing current exceeds that required to reach threshold at the next node
• The time between absolute and relative refractory periods
• The speed at which an action potential travels

Correct Answer: The margin by which depolarizing current exceeds that required to reach threshold at the next node

Q20. Use-dependent block of Na+ channels by local anesthetics means:

• Block increases with higher frequency of channel activation
• Block decreases with repetitive stimulation
• Block occurs only at rest
• Block is irreversible

Correct Answer: Block increases with higher frequency of channel activation

Q21. Which condition will increase nerve conduction velocity?

• Lower temperature
• Smaller axonal diameter
• Increased myelination
• Reduced internodal distance

Correct Answer: Increased myelination

Q22. Chronaxie is best described as:

• The minimal current to elicit an action potential with infinite duration
• The current needed at twice the rheobase duration to evoke a response
• The distance constant of an axon
• The number of action potentials per second

Correct Answer: The current needed at twice the rheobase duration to evoke a response

Q23. Which effect does extracellular hyperkalemia have on nerve excitability?

• Hyperpolarization and decreased excitability
• Depolarization and initial hyperexcitability followed by conduction block
• No effect on membrane potential
• Increased internodal resistance

Correct Answer: Depolarization and initial hyperexcitability followed by conduction block

Q24. The classical order of blockade by local anesthetics from most to least sensitive fibres is:

• Large motor fibres → small sensory fibres → autonomic fibres
• Small myelinated (autonomic) → small unmyelinated (pain) → large myelinated (motor)
• Large myelinated → small myelinated → small unmyelinated
• All fibres are equally sensitive

Correct Answer: Small myelinated (autonomic) → small unmyelinated (pain) → large myelinated (motor)

Q25. Which statement about membrane capacitance (Cm) is true?

• Higher Cm speeds passive voltage spread
• Myelin increases Cm
• Lower Cm reduces the time constant and speeds membrane charging
• Cm is independent of membrane structure

Correct Answer: Lower Cm reduces the time constant and speeds membrane charging

Q26. Antidromic conduction refers to:

• Action potential propagation from axon terminal toward the soma
• Normal orthodromic conduction from soma to terminal
• Conduction only in motor fibres
• Conduction that occurs during refractory period

Correct Answer: Action potential propagation from axon terminal toward the soma

Q27. Which factor best explains why large diameter axons conduct faster than small ones?

• Higher membrane capacitance in large axons
• Lower internal (axoplasmic) resistance in larger axons
• Greater density of potassium channels in small axons
• Increased extracellular resistance around large axons

Correct Answer: Lower internal (axoplasmic) resistance in larger axons

Q28. Which clinical sign suggests demyelination in peripheral nerves?

• Uniformly increased conduction velocity
• Conduction block and dispersed compound action potentials
• Improved reflexes
• Increased internodal lengths

Correct Answer: Conduction block and dispersed compound action potentials

Q29. How does lowered pH (acidic tissue) affect the action of local anesthetics?

• Increases the non-ionized form improving penetration and action
• Decreases the non-ionized form reducing penetration and slowing onset
• Has no effect on local anesthetic action
• Neutralizes the drug increasing potency

Correct Answer: Decreases the non-ionized form reducing penetration and slowing onset

Q30. Which fibre type carries rapidly conducted proprioceptive signals?

• Aα fibres
• Aδ fibres
• B fibres
• C fibres

Correct Answer: Aα fibres

Q31. Which statement about internodal length is correct?

• Shorter internodes always speed conduction
• Optimal internodal length maximizes conduction velocity; very short or very long internodes impair conduction
• Internodal length is irrelevant to conduction
• Longer internodes always decrease conduction velocity

Correct Answer: Optimal internodal length maximizes conduction velocity; very short or very long internodes impair conduction

Q32. Which change occurs at nodes of Ranvier compared to internodal regions?

• Lower density of ion channels
• Higher membrane capacitance
• High density of voltage-gated Na+ channels and low myelin coverage
• Increased myelin insulation

Correct Answer: High density of voltage-gated Na+ channels and low myelin coverage

Q33. Which pharmacologic agent causes persistent activation of Na+ channels leading to depolarization?

• Tetrodotoxin
• Veratridine
• Lidocaine
• Ouabain

Correct Answer: Veratridine

Q34. Accommodation in nerve fibres refers to:

• Increased excitability with slow depolarization
• Failure to fire in response to slowly rising depolarizing current due to sodium channel inactivation
• Action potential propagation at higher speeds
• Increased sodium channel availability

Correct Answer: Failure to fire in response to slowly rising depolarizing current due to sodium channel inactivation

Q35. Which physical change reduces membrane time constant (τ) and speeds response to current?

• Increased membrane capacitance
• Increased membrane resistance
• Decreased membrane capacitance
• Increased intracellular resistance

Correct Answer: Decreased membrane capacitance

Q36. Which fibre type primarily transmits fast, sharp pain?

• Aδ fibres
• Aβ fibres
• B fibres
• C fibres

Correct Answer: Aδ fibres

Q37. Which measurement from nerve conduction studies corresponds to conduction velocity?

• Peak-to-peak amplitude only
• Latency difference between stimulation points divided by distance
• Number of recruited motor units
• Resting membrane potential

Correct Answer: Latency difference between stimulation points divided by distance

Q38. Which statement about B fibres is correct?

• They are large myelinated motor fibres
• They are small myelinated autonomic fibres with moderate conduction velocity
• They are unmyelinated sensory pain fibres
• They are the fastest conducting fibres in peripheral nerves

Correct Answer: They are small myelinated autonomic fibres with moderate conduction velocity

Q39. During demyelination, what happens to the length constant (λ)?

• Length constant increases
• Length constant decreases
• Length constant remains unchanged
• Length constant becomes infinite

Correct Answer: Length constant decreases

Q40. Which structural cells produce myelin in the peripheral nervous system?

• Oligodendrocytes
• Astrocytes
• Schwann cells
• Microglia

Correct Answer: Schwann cells

Q41. Which is an expected electrophysiological change after focal demyelination?

• Decreased threshold for action potential generation
• Increased conduction velocity
• Temporal dispersion of compound action potential and conduction delay
• Improved saltatory conduction

Correct Answer: Temporal dispersion of compound action potential and conduction delay

Q42. Which statement about unmyelinated C fibres is true?

• They have nodes of Ranvier every few micrometers
• They conduct action potentials continuously without saltation
• They are responsible for proprioception
• They are fastest conducting fibres

Correct Answer: They conduct action potentials continuously without saltation

Q43. Which ionic movement underlies the repolarization phase of the action potential?

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

Correct Answer: Efflux of K+

Q44. Which factor is most likely to shift local anesthetic potency to favor stronger blockade?

• Lower lipid solubility of the drug
• Higher pKa reducing non-ionized fraction
• Increased lipid solubility enhancing membrane partitioning
• Reduced protein binding

Correct Answer: Increased lipid solubility enhancing membrane partitioning

Q45. Which effect will blocking voltage-gated K+ channels have on action potential waveform?

• Shorter action potential duration
• Prolonged repolarization and increased action potential duration
• Reduced amplitude of depolarization
• No effect on action potential duration

Correct Answer: Prolonged repolarization and increased action potential duration

Q46. Which property distinguishes internodal regions from nodes in myelinated axons?

• Internodes contain high densities of voltage-gated sodium channels
• Internodes are insulated and have few ion channels, reducing leakage
• Internodes are major sites of action potential initiation
• Internodes have higher capacitance than nodes

Correct Answer: Internodes are insulated and have few ion channels, reducing leakage

Q47. Tetrodotoxin (TTX) sensitivity varies among fibres because of differences in:

• Myelin composition only
• Subtypes of sodium channel expressed
• Axoplasmic potassium concentration
• Length constant exclusively

Correct Answer: Subtypes of sodium channel expressed

Q48. Which clinical test assesses peripheral nerve conduction and latency to detect demyelination?

• Electroencephalography (EEG)
• Nerve conduction study (NCS)
• Positron emission tomography (PET)
• Electrocardiography (ECG)

Correct Answer: Nerve conduction study (NCS)

Q49. Which change in membrane properties would most directly reduce the length constant (λ)?

• Increased membrane resistance
• Increased internal (axial) resistance
• Increased internodal distance
• Decreased intracellular resistance

Correct Answer: Increased internal (axial) resistance

Q50. Which statement best links pharmacology to nerve fibre properties?

• All drugs affect nerve fibres equally regardless of size or myelination
• Drug action depends on fibre diameter, myelination, firing frequency and channel state, influencing therapeutic and toxic effects
• Local anesthetics only affect synaptic transmission and not axonal conduction
• Toxins that block K+ channels have no impact on refractory periods

Correct Answer: Drug action depends on fibre diameter, myelination, firing frequency and channel state, influencing therapeutic and toxic effects

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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