Classification of nerve fibres MCQs With Answer

Classification of nerve fibres MCQs With Answer — This concise, Student-friendly post explains the classification of nerve fibres for B. Pharm students, focusing on clinical and pharmacological relevance. Learn about Erlanger‑Gasser and Lloyd‑Hunt systems, A, B, and C fibre subtypes (Aα, Aβ, Aγ, Aδ), myelination, diameter, conduction velocity, and functional roles in motor, sensory, and autonomic pathways. Understand how fibre type influences local anesthetic susceptibility, diabetic neuropathy, demyelinating diseases, and nerve conduction studies. Clear definitions and clinical correlations will strengthen your exam and practical pharmacology skills. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which classification system first divided nerve fibres into A, B, and C groups based on conduction velocity?

• Erlanger and Gasser classification
• Lloyd and Hunt classification
• Seddon classification
• Ranvier classification

Correct Answer: Erlanger and Gasser classification

Q2. Which fibre type is unmyelinated and transmits slow, diffuse pain and temperature?

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

Correct Answer: C fibres

Q3. Which A fibre subtype primarily mediates proprioception and motor efferent signals to skeletal muscle?

• Aα fibres
• Aβ fibres
• Aδ fibres
• Aγ fibres

Correct Answer: Aα fibres

Q4. In Lloyd and Hunt numeric grouping, which group corresponds to Aα fibres?

• Group I
• Group II
• Group III
• Group IV

Correct Answer: Group I

Q5. Which property most directly increases conduction velocity in a myelinated nerve fibre?

• Smaller axonal diameter
• Increased internodal myelin thickness and larger diameter
• Higher density of mitochondria
• Shorter node length alone

Correct Answer: Increased internodal myelin thickness and larger diameter

Q6. Which fibre type is primarily responsible for preganglionic autonomic transmission?

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

Correct Answer: B fibres

Q7. Which of the following sequences correctly ranks nerve fibres by decreasing conduction velocity?

• C > B > Aδ > Aα
• Aα > Aβ > Aδ > C
• B > C > Aα > Aβ
• Aδ > Aγ > Aβ > Aα

Correct Answer: Aα > Aβ > Aδ > C

Q8. Which feature distinguishes Aδ fibres from C fibres?

• Aδ fibres are unmyelinated; C fibres are myelinated
• Aδ fibres are myelinated and faster-conducting; C fibres are unmyelinated and slow
• Both are myelinated but Aδ are larger
• Both are unmyelinated but C fibres have nodes of Ranvier

Correct Answer: Aδ fibres are myelinated and faster-conducting; C fibres are unmyelinated and slow

Q9. Which nerve conduction study parameter is directly measured and used to infer fibre class dysfunction?

• Axonal mitochondrial count
• Conduction velocity
• Axonal width under microscope
• Resting membrane potential

Correct Answer: Conduction velocity

Q10. Which clinical sign suggests preferential loss of large myelinated Aβ fibres?

• Loss of temperature sensation only
• Painful burning in a glove-and-stocking distribution
• Loss of vibration and proprioception
• Excessive sweating from sympathetic overactivity

Correct Answer: Loss of vibration and proprioception

Q11. Which statement about saltatory conduction is correct?

• It occurs in unmyelinated fibres along the entire axon
• It increases conduction speed by jumping between nodes of Ranvier in myelinated fibres
• It decreases conduction velocity to conserve energy
• It only occurs in C fibres

Correct Answer: It increases conduction speed by jumping between nodes of Ranvier in myelinated fibres

Q12. Which fibre type carries fast, sharp pain sensations?

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

Correct Answer: Aδ fibres

Q13. Which of the following is a pharmacological implication of fibre classification for local anesthetic blockade?

• Large myelinated fibres are blocked before small unmyelinated fibres
• Small myelinated and small unmyelinated fibres are more susceptible than large myelinated fibres
• C fibres are resistant to all local anesthetics
• Myelination has no effect on anesthetic sensitivity

Correct Answer: Small myelinated and small unmyelinated fibres are more susceptible than large myelinated fibres

Q14. Which A fibre subtype primarily mediates discriminative touch and pressure?

• Aγ fibres
• Aβ fibres
• Aδ fibres
• C fibres

Correct Answer: Aβ fibres

Q15. In diabetic neuropathy, which fibre type is often affected earliest causing impaired pain and temperature?

• Large Aα fibres
• B fibres only
• Small unmyelinated C and small myelinated Aδ fibres
• Aβ fibres exclusively

Correct Answer: Small unmyelinated C and small myelinated Aδ fibres

Q16. Which structural component is essential for saltatory conduction?

• Continuous uniform myelin without nodes
• Nodes of Ranvier between myelinated internodes
• High concentration of mitochondria at internodes
• Absence of voltage-gated sodium channels at nodes

Correct Answer: Nodes of Ranvier between myelinated internodes

Q17. Which measurement correlates with axonal diameter and thus conduction velocity?

• Action potential amplitude only
• Time constant exclusively
• Space constant (length constant)
• Number of Schwann cells alone

Correct Answer: Space constant (length constant)

Q18. Which fibre type is most involved in autonomic postganglionic sympathetic vasoconstrictor signals?

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

Correct Answer: C fibres

Q19. Which clinical test best evaluates large myelinated fibre function?

• Quantitative thermal testing
• Nerve conduction velocity (NCV) with vibration sense exam
• Pain pressure threshold test only
• Sudomotor function test only

Correct Answer: Nerve conduction velocity (NCV) with vibration sense exam

Q20. Which change would you expect in demyelinating neuropathy?

• Increased conduction velocity
• Conduction block and slowed conduction velocity
• Selective increase in C fibre function
• No change in latency

Correct Answer: Conduction block and slowed conduction velocity

Q21. Which fibre type has the shortest refractory period and thus highest frequency firing capability?

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

Correct Answer: Aα fibres

Q22. Which statement about node of Ranvier ion channels is correct?

• Nodes are enriched in voltage-gated sodium channels to regenerate action potentials
• Nodes lack sodium channels and rely on passive spread only
• Nodes have only potassium channels and no sodium channels
• Nodes are only present in unmyelinated axons

Correct Answer: Nodes are enriched in voltage-gated sodium channels to regenerate action potentials

Q23. Which group of fibres is most susceptible to ischemic injury?

• Large myelinated Aα fibres
• Small myelinated B and small unmyelinated C fibres
• Only sensory fibres, not motor
• Fibres with the most myelin are most susceptible

Correct Answer: Small myelinated B and small unmyelinated C fibres

Q24. Which classification correlates Aα, Aβ, Aγ, Aδ to Group I–IV sensory groups?

• Aα = Group IV, Aδ = Group I
• Aα = Group I, Aβ = Group II, Aδ = Group III, C = Group IV
• Aα = Group II, Aβ = Group I, C = Group III
• No correlation exists between these systems

Correct Answer: Aα = Group I, Aβ = Group II, Aδ = Group III, C = Group IV

Q25. Which fibre property most influences the threshold for excitation by extracellular current?

• Axonal diameter and membrane resistance
• Length of myelin only
• Mitochondrial density exclusively
• Number of synaptic terminals

Correct Answer: Axonal diameter and membrane resistance

Q26. Which of the following best describes B fibres conduction characteristics?

• Large diameter, fastest conduction
• Small myelinated, moderate conduction velocity, autonomic preganglionic
• Unmyelinated, very slow conduction, pain transmission
• Equivalent to Aα in conduction speed

Correct Answer: Small myelinated, moderate conduction velocity, autonomic preganglionic

Q27. Why do myelinated fibres conduct more efficiently than unmyelinated fibres?

• Because myelin increases membrane capacitance dramatically
• Because myelin reduces capacitance and increases membrane resistance, facilitating faster electrotonic spread
• Because myelinated fibres lack nodes so action potentials are continuous
• Because myelinated fibres are always longer

Correct Answer: Because myelin reduces capacitance and increases membrane resistance, facilitating faster electrotonic spread

Q28. Which assessment helps distinguish axonal degeneration from demyelination?

• Skin biopsy only
• Electromyography and nerve conduction studies showing reduced amplitude (axonal) vs slowed velocity/prolonged latency (demyelinating)
• Serum sodium measurement
• Complete blood count

Correct Answer: Electromyography and nerve conduction studies showing reduced amplitude (axonal) vs slowed velocity/prolonged latency (demyelinating)

Q29. Which statement about conduction velocity and axon diameter is true?

• Conduction velocity decreases as axon diameter increases
• Conduction velocity increases with axon diameter, approximately proportional to diameter in myelinated fibres
• There is no relationship between diameter and velocity
• Only unmyelinated fibres are affected by diameter

Correct Answer: Conduction velocity increases with axon diameter, approximately proportional to diameter in myelinated fibres

Q30. Which fibre type mediates muscle spindle gamma motor efferents?

• Aγ fibres
• Aβ fibres
• Aα fibres
• C fibres

Correct Answer: Aγ fibres

Q31. Which pharmacological factor increases local anesthetic block of a nerve fibre?

• High local anesthetic pKa relative to physiological pH decreases block
• High frequency of nerve firing increases block due to use-dependence
• Lower concentration of anesthetic always increases block
• Myelination completely prevents block

Correct Answer: High frequency of nerve firing increases block due to use-dependence

Q32. Which component is NOT a determinant of internodal length in peripheral myelinated axons?

• Axonal diameter
• Myelin thickness
• Distance between Schwann cell nuclei only
• Metabolic state and development factors

Correct Answer: Distance between Schwann cell nuclei only

Q33. Which clinical feature reflects small fibre neuropathy?

• Loss of ankle reflexes alone
• Painful burning, altered temperature sensation, preserved vibration sense
• Isolated motor weakness with preserved pain sensation
• Only autonomic signs without sensory disturbance

Correct Answer: Painful burning, altered temperature sensation, preserved vibration sense

Q34. Which of the following best explains why larger diameter myelinated fibres conduct faster?

• They have higher internal resistance
• They have lower internal resistance and larger space constant for electrotonic spread
• They have fewer ion channels so APs are faster
• They lack nodes of Ranvier which speeds conduction

Correct Answer: They have lower internal resistance and larger space constant for electrotonic spread

Q35. Which experimental measure is used to estimate peripheral nerve myelination integrity?

• Compound muscle action potential amplitude only
• Nerve conduction velocity and distal latency
• Serum glucose concentration
• Heart rate variability exclusively

Correct Answer: Nerve conduction velocity and distal latency

Q36. Which statement about Aβ fibre dysfunction would be correct in neuropathic pain?

• Loss of Aβ input cannot cause allodynia
• Aberrant Aβ activity can contribute to tactile allodynia by abnormal central processing
• Aβ fibres only carry pain and their loss reduces allodynia
• Aβ fibres are unaffected in neuropathic pain syndromes

Correct Answer: Aberrant Aβ activity can contribute to tactile allodynia by abnormal central processing

Q37. Which ion channel density is highest at the node of Ranvier to support rapid conduction?

• Voltage-gated calcium channels mainly
• Voltage-gated sodium channels
• Na+/K+ ATPase only
• Ligand-gated chloride channels predominantly

Correct Answer: Voltage-gated sodium channels

Q38. Which factor could selectively impair conduction in myelinated fibres but spare unmyelinated fibres?

• Compression causing focal demyelination
• Hyperkalemia exclusively affects unmyelinated fibres
• Hypothermia only affects unmyelinated fibres
• Increased axonal diameter

Correct Answer: Compression causing focal demyelination

Q39. Which nerve fibre characteristic best predicts sensitivity to local anesthetics?

• Myelination status and diameter (small myelinated most sensitive)
• Only the neurotransmitter used at the terminal
• Length of the nerve alone
• Number of synapses along the axon

Correct Answer: Myelination status and diameter (small myelinated most sensitive)

Q40. Which clinical phenomenon occurs when small myelinated fibres are blocked before large fibres during regional anesthesia?

• Preservation of pain sensation while motor is lost first
• Loss of sympathetic tone, then pain, then touch, then motor function
• Motor block occurs before sensory block
• No autonomic effects are seen

Correct Answer: Loss of sympathetic tone, then pain, then touch, then motor function

Q41. In peripheral nerve injury, Wallerian degeneration primarily affects which part of the axon?

• Cell body only
• Distal segment of the axon distal to the lesion
• Proximal segment exclusively
• Only the myelin sheath without axonal degeneration

Correct Answer: Distal segment of the axon distal to the lesion

Q42. Which parameter is most reduced in axonal neuropathy compared to demyelinating neuropathy?

• Action potential amplitude
• Conduction velocity only
• Node of Ranvier length exclusively
• Myelin thickness only

Correct Answer: Action potential amplitude

Q43. Which fibre type primarily mediates itch and slow burning pain?

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

Correct Answer: C fibres

Q44. Which statement correctly relates fibre diameter to susceptibility to metabolic insult?

• Larger fibres are always more resistant to metabolic insult
• Small fibres, especially unmyelinated C fibres, are often more vulnerable to metabolic disturbances due to less trophic support
• Only motor fibres are affected by metabolic insults
• Fibre diameter has no influence on vulnerability

Correct Answer: Small fibres, especially unmyelinated C fibres, are often more vulnerable to metabolic disturbances due to less trophic support

Q45. Which of the following best describes the relationship between internodal length and conduction velocity?

• Longer internodes always decrease conduction speed
• There is an optimal internodal length increasing conduction; too short or too long internodes reduce efficiency
• Internodal length has no effect on conduction
• Only node length matters, not internodal length

Correct Answer: There is an optimal internodal length increasing conduction; too short or too long internodes reduce efficiency

Q46. Which diagnostic modality can quantify small fibre neuropathy when nerve conduction studies are normal?

• Sural nerve conduction velocity only
• Skin biopsy with intraepidermal nerve fibre density measurement
• Complete blood count
• Plain X‑ray of limb

Correct Answer: Skin biopsy with intraepidermal nerve fibre density measurement

Q47. Which fibre type would most likely show earliest conduction block with pressure-induced focal ischemia?

• Large Aα motor fibres
• Small myelinated B fibres and unmyelinated C fibres
• Aβ fibres exclusively
• Only autonomic fibres are affected

Correct Answer: Small myelinated B fibres and unmyelinated C fibres

Q48. Which change in nerve conduction study suggests demyelination rather than axonal loss?

• Markedly slowed conduction velocity with relatively preserved amplitudes
• Markedly reduced amplitude with normal conduction velocity
• Increased amplitude and conduction velocity
• No change in any parameter

Correct Answer: Markedly slowed conduction velocity with relatively preserved amplitudes

Q49. Which fibre type is primarily assessed by vibration sense testing?

• Small unmyelinated C fibres
• Large myelinated Aβ fibres
• B fibres only
• Aδ fibres mainly

Correct Answer: Large myelinated Aβ fibres

Q50. Which therapeutic consideration is important when designing drugs that target peripheral nerve excitability?

• Ignoring fibre type specificity because all fibres respond identically
• Considering fibre diameter, myelination, and channel expression to achieve selective effects and minimize side effects
• Designing drugs that increase myelin thickness directly overnight
• Only targeting central nervous system channels is relevant for peripheral excitability

Correct Answer: Considering fibre diameter, myelination, and channel expression to achieve selective effects and minimize side 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.

Mail- Sachin@pharmacyfreak.com