Conduction of nerve impulse MCQs With Answer

Conduction of nerve impulse MCQs With Answer — This concise guide is tailored for B. Pharm students revising neurophysiology and pharmacology fundamentals. It covers mechanisms of action potential generation, ionic basis of nerve conduction, myelination and saltatory conduction, refractory periods, and factors that alter conduction velocity. Questions also address pharmacological modulation by local anesthetics, channel blockers, and disease states such as demyelination and channelopathies. Ideal for exam prep, these MCQs clarify concepts like membrane potential, Nernst and Goldman equations, cable properties, and safety factor, while linking theory to drug action and clinical implications. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What ion influx primarily generates the rapid depolarization phase of an action potential in myelinated peripheral nerves?

• Sodium (Na+) influx through voltage-gated Na+ channels
• Potassium (K+) influx through voltage-gated K+ channels
• Calcium (Ca2+) influx through L-type Ca2+ channels
• Chloride (Cl-) influx through GABA-gated channels

Correct Answer: Sodium (Na+) influx through voltage-gated Na+ channels

Q2. Which structural feature allows saltatory conduction in myelinated axons?

• Continuous distribution of ion channels along the axon
• Presence of nodes of Ranvier with concentrated sodium channels
• Uniform internodal capacitance
• High density of potassium channels at internodes

Correct Answer: Presence of nodes of Ranvier with concentrated sodium channels

Q3. Which equation is used to calculate the equilibrium potential for a single ion species across the membrane?

• Goldman-Hodgkin-Katz equation
• Nernst equation
• Hodgkin-Huxley model
• Ohm’s law

Correct Answer: Nernst equation

Q4. Which factor most increases conduction velocity in myelinated axons?

• Decreased axon diameter
• Increased internodal length up to an optimum
• Higher membrane capacitance
• Increased axial resistance

Correct Answer: Increased internodal length up to an optimum

Q5. The refractory period immediately following an action potential during which another action potential cannot be generated is called:

• Relative refractory period
• Absolute refractory period
• Supernormal period
• Afterhyperpolarization

Correct Answer: Absolute refractory period

Q6. Local anesthetics like lidocaine block nerve conduction primarily by:

• Blocking voltage-gated potassium channels externally
• Inhibiting neurotransmitter reuptake at the synapse
• Binding to and stabilizing the inactivated state of voltage-gated sodium channels
• Increasing membrane permeability to chloride

Correct Answer: Binding to and stabilizing the inactivated state of voltage-gated sodium channels

Q7. Which nerve fiber type has the slowest conduction velocity?

• A-alpha (Aα) fibers
• A-beta (Aβ) fibers
• A-delta (Aδ) fibers
• C fibers

Correct Answer: C fibers

Q8. The Goldman equation differs from the Nernst equation because it:

• Calculates equilibrium potential for a single ion
• Accounts for multiple ions and their permeabilities
• Is only valid for capacitive currents
• Predicts action potential amplitude directly

Correct Answer: Accounts for multiple ions and their permeabilities

Q9. Which change would shorten the membrane time constant (τ) and speed up membrane charging?

• Increased membrane resistance (Rm)
• Decreased membrane capacitance (Cm)
• Increased axial resistance (Ri)
• Decreased external ion concentration

Correct Answer: Decreased membrane capacitance (Cm)

Q10. Saltatory conduction increases conduction velocity mainly by:

• Reducing internodal resistance
• Increasing transmembrane ion flux at internodes
• Reducing the effective membrane capacitance and limiting ion exchange to nodes
• Enhancing synaptic transmission

Correct Answer: Reducing the effective membrane capacitance and limiting ion exchange to nodes

Q11. Which of the following best describes the safety factor for conduction?

• The ratio of ionic to capacitive current during depolarization
• The margin by which local depolarization exceeds threshold to ensure propagation
• The distance between nodes of Ranvier
• The refractory period duration relative to spike width

Correct Answer: The margin by which local depolarization exceeds threshold to ensure propagation

Q12. A demyelinating disease primarily reduces conduction velocity by:

• Increasing sodium channel density at nodes
• Lowering axial resistance
• Increasing membrane capacitance and decreasing internodal insulation
• Enhancing saltatory conduction

Correct Answer: Increasing membrane capacitance and decreasing internodal insulation

Q13. Which ion channel mutation would most likely produce hyperexcitability and spontaneous firing?

• Loss-of-function mutation in voltage-gated Na+ channels
• Gain-of-function mutation in voltage-gated Na+ channels
• Loss-of-function mutation in voltage-gated K+ channels
• Increased Cl- conductance via GABA receptors

Correct Answer: Gain-of-function mutation in voltage-gated Na+ channels

Q14. The Hodgkin-Huxley model primarily provides:

• A structural map of myelinated axons
• Quantitative equations describing ionic currents and action potential dynamics
• An empirical rule for synaptic strength
• A method to measure nerve conduction velocity clinically

Correct Answer: Quantitative equations describing ionic currents and action potential dynamics

Q15. Tetrodotoxin (TTX) blocks nerve conduction by binding to:

• Extracellular pore of voltage-gated Na+ channels
• Intracellular inactivation gate of Na+ channels
• Voltage-gated K+ channels at nodes
• Ligand-gated acetylcholine receptors

Correct Answer: Extracellular pore of voltage-gated Na+ channels

Q16. Which parameter determines the length constant (λ) in cable theory?

• Membrane capacitance alone
• Axial resistance and membrane resistance
• Action potential amplitude
• External ion concentrations

Correct Answer: Axial resistance and membrane resistance

Q17. Conduction block where action potential fails to propagate past a region despite upstream firing is often due to:

• Increased safety factor
• Local anesthetic action or severe demyelination reducing local depolarization below threshold
• Increased internodal length improving conduction
• Enhanced sodium channel recruitment

Correct Answer: Local anesthetic action or severe demyelination reducing local depolarization below threshold

Q18. Compound action potentials recorded from peripheral nerves represent:

• Electrical activity of a single axon only
• Summed activity of many axons with different conduction velocities
• Pure synaptic potentials at the neuromuscular junction
• Only motor fiber activity

Correct Answer: Summed activity of many axons with different conduction velocities

Q19. Which ion is primarily responsible for the afterhyperpolarization (AHP) following an action potential?

• Influx of Na+
• Efflux of K+ through voltage-gated K+ channels
• Influx of Ca2+ through N-type channels only
• Influx of Cl- through glycine receptors

Correct Answer: Efflux of K+ through voltage-gated K+ channels

Q20. The effect of increasing extracellular potassium concentration ([K+]o) on resting membrane potential is to:

• Hyperpolarize the membrane
• Depolarize the membrane toward threshold
• Have no effect due to homeostasis
• Increase membrane capacitance

Correct Answer: Depolarize the membrane toward threshold

Q21. Which statement about saltatory conduction is correct?

• Ions cross the membrane uniformly along the entire axon
• Action potentials are regenerated only at the nodes, not at internodes
• Myelin increases membrane capacitance at internodes
• Internodal regions have a higher density of Na+ channels than nodes

Correct Answer: Action potentials are regenerated only at the nodes, not at internodes

Q22. Which pharmacological agent is most likely to slow conduction by blocking voltage-gated Na+ channels in a use-dependent manner?

• Sodium chloride
• Lidocaine
• Potassium permanganate
• Acetylcholine

Correct Answer: Lidocaine

Q23. Which fiber type primarily conducts proprioceptive information from muscle spindles?

• A-alpha (Aα) fibers
• A-delta (Aδ) fibers
• C fibers
• B fibers

Correct Answer: A-alpha (Aα) fibers

Q24. A decrease in membrane resistance (Rm) will have what effect on the length constant (λ)?

• Increase λ
• Decrease λ
• No effect on λ
• Convert λ to the time constant

Correct Answer: Decrease λ

Q25. Which clinical test measures peripheral nerve conduction velocity?

• Electroencephalography (EEG)
• Electromyography (EMG) with nerve conduction studies
• Magnetic resonance imaging (MRI)
• Positron emission tomography (PET)

Correct Answer: Electromyography (EMG) with nerve conduction studies

Q26. The nodal concentration of sodium channels is highest at:

• Internodes under myelin
• Nodes of Ranvier
• Axon hillock only
• Presynaptic terminal exclusively

Correct Answer: Nodes of Ranvier

Q27. Which property distinguishes action potential propagation in unmyelinated axons compared to myelinated axons?

• Saltatory conduction occurs in unmyelinated axons
• Conduction is continuous and slower in unmyelinated axons
• Unmyelinated axons have nodes of Ranvier every 1 mm
• Unmyelinated axons have higher internodal capacitance

Correct Answer: Conduction is continuous and slower in unmyelinated axons

Q28. Which mechanism best explains why temperature affects nerve conduction velocity?

• Temperature alters axon diameter directly
• Temperature affects ion channel kinetics and membrane resistance
• Temperature changes internodal length instantly
• Temperature alters extracellular myelin composition permanently

Correct Answer: Temperature affects ion channel kinetics and membrane resistance

Q29. Phenytoin and carbamazepine reduce neuronal excitability mainly by:

• Blocking calcium channels in the synapse
• Enhancing GABAergic chloride conductance exclusively
• Stabilizing the inactivated state of voltage-gated sodium channels
• Inhibiting potassium channel opening

Correct Answer: Stabilizing the inactivated state of voltage-gated sodium channels

Q30. Which term describes passive spread of voltage without action potential regeneration?

• Saltatory conduction
• Electrotonic or graded conduction
• Action potential propagation
• Synaptic transmission

Correct Answer: Electrotonic or graded conduction

Q31. The maximum frequency at which a neuron can fire action potentials is limited primarily by:

• Action potential amplitude
• Absolute and relative refractory periods
• Internodal length only
• Membrane capacitance alone

Correct Answer: Absolute and relative refractory periods

Q32. In nerve conduction studies, slowing of conduction velocity with preserved amplitude suggests:

• Axonal degeneration
• Demyelination or conduction block
• Neuromuscular junction failure
• Complete transection of the nerve

Correct Answer: Demyelination or conduction block

Q33. Which structural cell forms myelin in the central nervous system (CNS)?

• Schwann cells
• Oligodendrocytes
• Satellite cells
• Astrocytes

Correct Answer: Oligodendrocytes

Q34. Which property of myelin reduces membrane capacitance?

• Multiple lipid layers increasing insulation thickness
• Increased density of ion channels at internodes
• Reduced extracellular ion concentration
• Increased cytoplasmic volume of the axon

Correct Answer: Multiple lipid layers increasing insulation thickness

Q35. Which of the following is a characteristic of A-delta fibers?

• Slow conduction and unmyelinated
• Fast conduction, large diameter, proprioception
• Thinly myelinated, convey sharp pain and temperature
• Preganglionic autonomic fiber exclusively

Correct Answer: Thinly myelinated, convey sharp pain and temperature

Q36. Which ion movement primarily sets the resting membrane potential in neurons?

• Sodium influx down its concentration gradient
• Potassium efflux through leak channels and active pumping by Na+/K+ ATPase
• Chloride active transport outward
• Calcium extrusion only

Correct Answer: Potassium efflux through leak channels and active pumping by Na+/K+ ATPase

Q37. Which drug intoxication is classically associated with blockade of voltage-gated sodium channels leading to paralysis?

• Organophosphate poisoning
• Tetrodotoxin (pufferfish) poisoning
• Acetaminophen overdose
• Atropine overdose

Correct Answer: Tetrodotoxin (pufferfish) poisoning

Q38. Slow inactivation of sodium channels contributes to which phenomenon?

• Immediate activation of K+ channels
• Longer-term modulation of excitability during sustained depolarization
• Rapid recovery from absolute refractory period
• Increase in membrane capacitance

Correct Answer: Longer-term modulation of excitability during sustained depolarization

Q39. Which of these best describes internodal regions under myelin?

• High density of voltage-gated Na+ channels
• Relatively low membrane capacitance and low channel density
• Primary sites of neurotransmitter release
• Regions of action potential initiation only

Correct Answer: Relatively low membrane capacitance and low channel density

Q40. Which condition is most likely to reduce safety factor and produce conduction block?

• Mild hyperkalemia that slightly depolarizes membrane
• Partial demyelination or local anesthetic application
• Increased internodal length within physiological range
• Increased sodium channel expression at nodes

Correct Answer: Partial demyelination or local anesthetic application

Q41. Which parameter is increased by myelination, enhancing conduction velocity?

• Membrane capacitance at nodes
• Membrane resistance across internodes
• Axial resistance inside the axon
• Number of synapses per axon

Correct Answer: Membrane resistance across internodes

Q42. Which toxin blocks sodium channels from the intracellular side and is used experimentally to study channel gating?

• Tetrodotoxin (TTX)
• Saxitoxin
• Lidocaine
• Batrachotoxin

Correct Answer: Lidocaine

Q43. Which ionic current predominates during the repolarization phase of the action potential?

• Voltage-gated Na+ inward current
• Voltage-gated K+ outward current
• Leak Cl- inward current
• Voltage-gated Ca2+ inward current

Correct Answer: Voltage-gated K+ outward current

Q44. The phenomenon where a weaker-than-threshold stimulus can trigger an action potential during a brief period after the refractory period is called:

• Absolute refractory period
• Relative refractory period or supernormal period depending on timing
• Accommodation only
• Conduction block

Correct Answer: Relative refractory period or supernormal period depending on timing

Q45. Which cellular event increases safety factor at a node of Ranvier?

• Decrease in local sodium channel density
• Increased local sodium current and larger depolarizing charge transfer to next node
• Increased internodal capacitance
• Elevated extracellular potassium causing inactivation

Correct Answer: Increased local sodium current and larger depolarizing charge transfer to next node

Q46. In peripheral neuropathy with axonal degeneration, nerve conduction studies typically show:

• Normal amplitude and slowed velocity
• Reduced amplitude and relatively preserved velocity early
• Increased conduction velocity
• Only changes in central conduction

Correct Answer: Reduced amplitude and relatively preserved velocity early

Q47. Which of the following best distinguishes a channelopathy from demyelination clinically?

• Channelopathies always cause sensory loss only
• Channelopathies often produce episodic symptoms related to gating defects, while demyelination causes conduction slowing and dispersion
• Demyelination causes episodic paralysis, channelopathies cause continuous conduction block
• They are clinically identical and indistinguishable

Correct Answer: Channelopathies often produce episodic symptoms related to gating defects, while demyelination causes conduction slowing and dispersion

Q48. Which measurement in nerve conduction studies indicates demyelination most directly?

• Reduced compound muscle action potential amplitude only
• Marked slowing of conduction velocity and prolonged distal latency
• Increased amplitude with normal velocity
• Shortened latency to muscle response

Correct Answer: Marked slowing of conduction velocity and prolonged distal latency

Q49. Which physiological concept explains decremental conduction in high-frequency stimulation leading to conduction failure?

• Increased Na+/K+ ATPase function
• Accumulation of extracellular K+, sodium channel inactivation, and reduced safety factor
• Immediate remyelination during stimulation
• Decreased axoplasmic resistance

Correct Answer: Accumulation of extracellular K+, sodium channel inactivation, and reduced safety factor

Q50. Which feature of myelinated nerve fibers allows energy-efficient rapid conduction?

• Continuous opening of Na+ channels along the axon
• Localization of ion exchange to nodes, reducing total ion pumping and metabolic cost
• High constant leak conductance across internodes
• Permanent depolarization of internodes

Correct Answer: Localization of ion exchange to nodes, reducing total ion pumping and metabolic cost

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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