Nerve impulse MCQs With Answer are essential study tools for B. Pharm students preparing for pharmacology, physiology, and therapeutics exams. This concise, keyword-rich introduction focuses on nerve impulse concepts such as action potential, resting membrane potential, ion channels, saltatory conduction, refractory periods, synaptic transmission, and pharmacological modulators like local anesthetics and channel blockers. These MCQs emphasize clinical relevance and drug mechanisms that target neuronal excitability, making them ideal for deepening understanding and improving recall. Questions cover ionic bases, electrophysiology models, conduction properties, and drug interactions with channels and receptors. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. Which ion primarily determines the resting membrane potential in neurons?
- Calcium (Ca2+)
- Potassium (K+)
- Sodium (Na+)
- Chloride (Cl-)
Correct Answer: Potassium (K+)
Q2. The Nernst equation is used to calculate which of the following?
- Membrane capacitance
- Equilibrium potential for a single ion
- Total ionic current through the membrane
- Membrane time constant
Correct Answer: Equilibrium potential for a single ion
Q3. The rapid upstroke (phase 0) of a neuronal action potential is mainly due to:
- Opening of voltage-gated K+ channels
- Opening of voltage-gated Na+ channels
- Activation of Na+/K+ ATPase
- Increased Cl- conductance
Correct Answer: Opening of voltage-gated Na+ channels
Q4. The absolute refractory period of an action potential is primarily caused by:
- Delayed opening of K+ channels
- Inactivation of voltage-gated Na+ channels
- Activation of Na+/K+ pump
- Increased membrane capacitance
Correct Answer: Inactivation of voltage-gated Na+ channels
Q5. Saltatory conduction refers to action potential propagation that:
- Occurs continuously along unmyelinated axons
- Jumps between nodes of Ranvier in myelinated axons
- Depends on synaptic transmission between segments
- Is slower than conduction in unmyelinated fibers
Correct Answer: Jumps between nodes of Ranvier in myelinated axons
Q6. The primary role of the node of Ranvier is to:
- Insulate the axon electrically
- Store neurotransmitters
- Regenerate the action potential via high density of ion channels
- Decrease internodal capacitance
Correct Answer: Regenerate the action potential via high density of ion channels
Q7. Myelination increases conduction velocity chiefly by:
- Increasing membrane capacitance and decreasing resistance
- Increasing membrane resistance and decreasing capacitance
- Increasing internal resistance of the axon
- Enhancing neurotransmitter release at nodes
Correct Answer: Increasing membrane resistance and decreasing capacitance
Q8. The length constant (lambda) is increased by which change?
- Decreased membrane resistance
- Increased internal (axial) resistance
- Increased membrane resistance
- Increased membrane capacitance
Correct Answer: Increased membrane resistance
Q9. Local anesthetics produce analgesia primarily by:
- Blocking voltage-gated calcium channels
- Blocking voltage-gated potassium channels
- Blocking voltage-gated sodium channels
- Enhancing GABAergic transmission
Correct Answer: Blocking voltage-gated sodium channels
Q10. Tetrodotoxin (TTX) causes paralysis by binding to and blocking which channel?
- Voltage-gated K+ channels
- Voltage-gated Na+ channels
- Ligand-gated NMDA receptors
- Voltage-gated Ca2+ channels
Correct Answer: Voltage-gated Na+ channels
Q11. Hyperkalemia (elevated extracellular K+) on neuronal membranes typically causes:
- Hyperpolarization, making firing less likely
- Depolarization, making the resting potential less negative
- No change in membrane potential
- Increased chloride conductance
Correct Answer: Depolarization, making the resting potential less negative
Q12. During the relative refractory period, an action potential can be initiated if:
- No additional stimulus is applied
- A weaker than normal stimulus is applied
- A stronger than normal stimulus is applied
- Only hyperpolarizing current is applied
Correct Answer: A stronger than normal stimulus is applied
Q13. The Hodgkin-Huxley model provides a quantitative description of:
- Synaptic vesicle recycling
- Ionic currents and gating variables underlying the action potential
- Neurotransmitter receptor subtypes
- Long-term synaptic plasticity mechanisms
Correct Answer: Ionic currents and gating variables underlying the action potential
Q14. Demyelination of an axon would most likely cause which effect on conduction safety factor?
- Increase safety factor
- No change in safety factor
- Decrease safety factor
- Completely eliminate ionic currents
Correct Answer: Decrease safety factor
Q15. Voltage-gated K+ channels mainly contribute to which phase of the action potential?
- Depolarization phase
- Repolarization and afterhyperpolarization
- Resting membrane potential generation via pumps
- Fast sodium inactivation
Correct Answer: Repolarization and afterhyperpolarization
Q16. Which of the following is an advantage of saltatory conduction?
- Decreased conduction velocity
- Higher energy consumption
- Faster conduction with lower energy cost
- Continuous regeneration that uses more ATP
Correct Answer: Faster conduction with lower energy cost
Q17. A compound action potential recorded from a peripheral nerve represents:
- The ionic current through a single neuron
- The summed action potentials of many axons in the nerve
- Only the conduction in motor fibers
- A measure of synaptic potentials at the neuromuscular junction
Correct Answer: The summed action potentials of many axons in the nerve
Q18. Myelin in the peripheral nervous system is produced by which cells?
- Microglia
- Oligodendrocytes
- Schwann cells
- Astrocytes
Correct Answer: Schwann cells
Q19. Neuronal threshold refers to the membrane potential at which:
- The neuron becomes refractory permanently
- An action potential is triggered due to net inward current
- Sodium channels close and potassium channels open
- Synaptic vesicles are released
Correct Answer: An action potential is triggered due to net inward current
Q20. Accommodation in a nerve fiber is best described as:
- Increased excitability during rapid stimulation
- Progressive decrease in excitability with sustained subthreshold depolarization
- Immediate firing in response to any depolarizing pulse
- Failure of Na+/K+ pump
Correct Answer: Progressive decrease in excitability with sustained subthreshold depolarization
Q21. Lidocaine exhibits use-dependent block of sodium channels because it:
- Binds preferentially to closed channels
- Binds preferentially to open or inactivated channels
- Increases channel conductance
- Blocks potassium channels instead
Correct Answer: Binds preferentially to open or inactivated channels
Q22. An excitatory postsynaptic potential (EPSP) is typically produced by increased conductance to which ion?
- Chloride (Cl-)
- Potassium (K+)
- Sodium (Na+)
- Calcium pump activity
Correct Answer: Sodium (Na+)
Q23. An inhibitory postsynaptic potential (IPSP) commonly results from increased permeability to:
- Sodium (Na+)
- Potassium (K+) or chloride (Cl-)
- Glucose
- Sodium-potassium pump activation only
Correct Answer: Potassium (K+) or chloride (Cl-)
Q24. NMDA-type glutamate receptors differ from AMPA receptors because NMDA receptors:
- Are purely ligand-gated with no voltage dependence
- Require both ligand binding and depolarization to remove Mg2+ block and are permeable to Ca2+
- Are selective only for K+
- Are inhibitory receptors producing IPSPs
Correct Answer: Require both ligand binding and depolarization to remove Mg2+ block and are permeable to Ca2+
Q25. The Na+/K+ ATPase contributes to nerve function by:
- Generating action potentials directly
- Maintaining Na+ and K+ concentration gradients using ATP
- Allowing passive diffusion of ions
- Creating gap junctions between neurons
Correct Answer: Maintaining Na+ and K+ concentration gradients using ATP
Q26. Increasing membrane capacitance in an axon will:
- Speed up the rate of voltage change
- Slow the rate of voltage change
- Have no effect on membrane dynamics
- Reduce internal resistance only
Correct Answer: Slow the rate of voltage change
Q27. The membrane time constant (tau) is defined as:
- Membrane resistance divided by membrane capacitance
- Membrane capacitance divided by membrane resistance
- Membrane resistance multiplied by membrane capacitance
- Internal resistance multiplied by axon length
Correct Answer: Membrane resistance multiplied by membrane capacitance
Q28. Which statement best describes the “all-or-none” principle of action potentials?
- Action potential amplitude increases with stronger stimulus
- Action potentials occur only in motor neurons
- Once threshold is reached, an action potential of fixed amplitude is produced
- Action potentials summate linearly to produce a larger spike
Correct Answer: Once threshold is reached, an action potential of fixed amplitude is produced
Q29. The voltage-clamp technique is primarily used to:
- Measure membrane capacitance only
- Record ionic currents while holding membrane potential constant
- Visualize single ion channels directly
- Measure neurotransmitter concentrations
Correct Answer: Record ionic currents while holding membrane potential constant
Q30. The patch-clamp technique is especially valuable because it can:
- Measure whole-brain electrical activity noninvasively
- Record currents from single ion channels with high resolution
- Replace the need for voltage clamp
- Image ion channel structure directly
Correct Answer: Record currents from single ion channels with high resolution
Q31. Botulinum toxin causes flaccid paralysis by:
- Blocking voltage-gated Na+ channels
- Cleaving SNARE proteins and preventing acetylcholine release
- Inhibiting the Na+/K+ pump
- Activating GABA receptors
Correct Answer: Cleaving SNARE proteins and preventing acetylcholine release
Q32. The synaptic delay at a chemical synapse is mainly due to:
- Axonal conduction time only
- Diffusion of neurotransmitter across the synaptic cleft and vesicle fusion processes
- The time for postsynaptic action potential generation exclusively
- Reuptake of neurotransmitter into the presynaptic terminal
Correct Answer: Diffusion of neurotransmitter across the synaptic cleft and vesicle fusion processes
Q33. Fast ionotropic synaptic transmission is mediated by:
- G-protein coupled receptors
- Ion channel-linked receptors such as AMPA receptors
- Intracellular second messengers only
- Changes in gene transcription
Correct Answer: Ion channel-linked receptors such as AMPA receptors
Q34. Metabotropic receptors typically produce their effects by:
- Directly forming ion channels that open instantaneously
- Activating G-proteins and second messenger cascades
- Blocking axonal conduction physically
- Causing immediate membrane depolarization only
Correct Answer: Activating G-proteins and second messenger cascades
Q35. Conduction velocity is generally higher in axons that are:
- Small diameter and unmyelinated
- Large diameter and myelinated
- Small diameter and myelinated
- Large diameter and unmyelinated
Correct Answer: Large diameter and myelinated
Q36. Multiple sclerosis primarily affects which of the following?
- Peripheral nerve Schwann cell myelin
- Central nervous system oligodendrocyte myelin
- Neuromuscular junction acetylcholine receptors
- Voltage-gated sodium channels exclusively
Correct Answer: Central nervous system oligodendrocyte myelin
Q37. The absolute refractory period limits the maximum:
- Amplitude of action potentials
- Duration of synaptic vesicle release
- Firing frequency of a neuron
- Size of the axon
Correct Answer: Firing frequency of a neuron
Q38. Afterhyperpolarization following an action potential is mainly mediated by:
- Fast inward sodium currents
- Increased potassium conductance
- Chloride influx through NMDA receptors
- Immediate activation of Na+/K+ pump alone
Correct Answer: Increased potassium conductance
Q39. Fast inactivation of voltage-gated sodium channels during an action potential is due to:
- Closure of the activation gate
- Opening of an inactivation gate that blocks the pore
- Permanent channel degradation
- Immediate potassium channel opening only
Correct Answer: Opening of an inactivation gate that blocks the pore
Q40. Which fiber type conducts action potentials fastest?
- Small unmyelinated fibers (C fibers)
- Small myelinated sensory fibers
- Large myelinated motor fibers (A-alpha)
- Large unmyelinated fibers
Correct Answer: Large myelinated motor fibers (A-alpha)
Q41. Potassium channel selectivity for K+ ions is primarily achieved by:
- ATP binding to the channel pore
- A selectivity filter that coordinates dehydrated K+ ions
- Blocking Na+ by internal Mg2+
- Voltage-sensing S4 segments only
Correct Answer: A selectivity filter that coordinates dehydrated K+ ions
Q42. Use-dependent block of sodium channels by antiarrhythmic drugs means the drug:
- Preferentially binds to resting closed channels
- Preferentially binds to channels during repetitive activation
- Only binds to potassium channels
- Enhances sodium currents during high-frequency firing
Correct Answer: Preferentially binds to channels during repetitive activation
Q43. Inhibition of presynaptic voltage-gated Ca2+ channels will primarily cause:
- Increased neurotransmitter release
- Decreased neurotransmitter release
- No effect on synaptic transmission
- Enhanced postsynaptic receptor sensitivity
Correct Answer: Decreased neurotransmitter release
Q44. Nodes of Ranvier are enriched in which channels to enable saltatory conduction?
- Ligand-gated Cl- channels
- Voltage-gated Na+ channels
- Voltage-gated Ca2+ channels only
- High density of Na+/K+ pumps exclusively
Correct Answer: Voltage-gated Na+ channels
Q45. Which toxin is well-known for blocking neuronal voltage-gated sodium channels?
- Tetrodotoxin (TTX)
- Curare
- Strychnine
- Atropine
Correct Answer: Tetrodotoxin (TTX)
Q46. Excitatory synapses typically produce which change in the postsynaptic membrane?
- Hyperpolarization via Cl- influx
- Depolarization by increasing Na+ conductance
- Permanent membrane depolarization
- Immediate axonal branching
Correct Answer: Depolarization by increasing Na+ conductance
Q47. In peripheral nerve conduction studies, demyelination is expected to cause:
- Decreased latency and increased amplitude
- Increased latency and possible conduction block
- No change in conduction velocity
- Only changes in synaptic delay
Correct Answer: Increased latency and possible conduction block
Q48. The safety factor for conduction is best defined as:
- The ratio of axon diameter to myelin thickness
- The margin of current available to depolarize the next node to threshold
- The absolute refractory period duration
- The amount of neurotransmitter released per impulse
Correct Answer: The margin of current available to depolarize the next node to threshold
Q49. The alpha subunit of voltage-gated sodium channels is important because it:
- Forms the ion-conducting pore and gating machinery
- Is purely regulatory with no pore function
- Is only present in cardiac tissue
- Is responsible for vesicle docking at synapses
Correct Answer: Forms the ion-conducting pore and gating machinery
Q50. A common pharmacological target for many antiepileptic drugs is which mechanism?
- Enhancement of voltage-gated sodium channel activity
- Blocking GABAergic transmission
- Inhibition of voltage-gated sodium channels or enhancement of GABAergic inhibition
- Activation of NMDA receptors to increase excitability
Correct Answer: Inhibition of voltage-gated sodium channels or enhancement of GABAergic inhibition

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