Generation of nerve impulse MCQs With Answer

Generation of nerve impulse MCQs With Answer is a focused set of practice questions designed for B. Pharm students to master neuronal physiology and pharmacological modulation of action potentials. This introduction and question bank cover key concepts such as resting membrane potential, Nernst and Goldman equations, voltage-gated ion channels, threshold, refractory periods, saltatory conduction, and drug/toxin effects on excitability. Emphasis is on clear mechanisms, ionic currents, and clinical relevance—local anesthetics, tetrodotoxin, channelopathies and demyelination—so you build both conceptual depth and exam-ready recall. The language is simple, informative and tailored to pharmacy curricula and pharmacology contexts. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What primarily determines the resting membrane potential of a neuron?

• Potassium (K+) leak channels and the K+ concentration gradient across the membrane
• Opening of voltage-gated Na+ channels
• Synaptic release of neurotransmitters
• Extracellular calcium concentration only

Correct Answer: Potassium (K+) leak channels and the K+ concentration gradient across the membrane

Q2. The Nernst equation is used to calculate which of the following?

• The equilibrium (reversal) potential for a single ionic species
• The membrane potential considering multiple ion permeabilities
• The rate of action potential propagation
• The concentration of ATP in the neuron

Correct Answer: The equilibrium (reversal) potential for a single ionic species

Q3. The threshold for action potential initiation is best described as:

• The membrane potential at which voltage-gated Na+ channels open rapidly
• The most positive membrane potential during an action potential
• The resting membrane potential of the neuron
• The equilibrium potential of potassium

Correct Answer: The membrane potential at which voltage-gated Na+ channels open rapidly

Q4. The rising phase (depolarization) of the neuronal action potential is mainly due to:

• Rapid opening of voltage-gated Na+ channels with inward Na+ current
• Opening of voltage-gated K+ channels with outward K+ current
• Activation of the Na+/K+ ATPase pump
• Influx of chloride ions through GABA receptors

Correct Answer: Rapid opening of voltage-gated Na+ channels with inward Na+ current

Q5. Typical peak membrane potential reached during an action potential in many neurons is approximately:

• +30 mV
• -90 mV
• -55 mV
• 0 mV

Correct Answer: +30 mV

Q6. Repolarization of the action potential is primarily caused by:

• Opening of voltage-gated K+ channels and efflux of K+
• Opening of voltage-gated Ca2+ channels and influx of Ca2+
• Increased activity of Na+/K+ ATPase within milliseconds
• Sustained Na+ influx through persistent Na+ channels

Correct Answer: Opening of voltage-gated K+ channels and efflux of K+

Q7. After-hyperpolarization (AHP) that follows an action potential is mainly due to:

• Activation of slow K+ conductances that outlast the AP
• Rapid re-opening of Na+ channels
• Influx of chloride ions through excitatory receptors
• Immediate reversal of the Na+/K+ pump direction

Correct Answer: Activation of slow K+ conductances that outlast the AP

Q8. The absolute refractory period occurs because:

• Voltage-gated Na+ channels are in the inactivated state and cannot reopen
• Membrane potential is at the peak of the action potential only
• Voltage-gated K+ channels are fully closed
• Synaptic inputs are temporarily blocked

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

Q9. The relative refractory period is characterized by:

• Partial recovery of Na+ channels and increased K+ conductance making AP initiation harder
• Complete readiness to fire another action potential with same amplitude
• Total block of Na+/K+ ATPase
• Absolute inability to generate any action potential

Correct Answer: Partial recovery of Na+ channels and increased K+ conductance making AP initiation harder

Q10. Saltatory conduction refers to:

• Action potentials jumping between nodes of Ranvier in myelinated axons
• Continuous propagation along unmyelinated axons
• Random firing of action potentials in dendrites
• Spontaneous transmitter release at the synapse

Correct Answer: Action potentials jumping between nodes of Ranvier in myelinated axons

Q11. Which two factors most increase conduction velocity in peripheral nerves?

• Large axonal diameter and myelination
• Short axon length and low extracellular calcium
• High membrane capacitance and small diameter
• Increased synaptic inputs and neurotransmitter release

Correct Answer: Large axonal diameter and myelination

Q12. Local anesthetics like lidocaine produce anesthesia mainly by:

• Blocking voltage-gated Na+ channels and preventing action potential propagation
• Activating voltage-gated K+ channels to hyperpolarize the nerve
• Inhibiting the Na+/K+ ATPase pump directly
• Blocking acetylcholine receptors at neuromuscular junctions

Correct Answer: Blocking voltage-gated Na+ channels and preventing action potential propagation

Q13. Tetrodotoxin (TTX) exerts its neurotoxic effect by:

• Blocking voltage-gated Na+ channels at the outer pore and preventing Na+ entry
• Blocking voltage-gated K+ channels
• Inhibiting the Na+/K+ ATPase directly
• Binding to GABA receptors and causing excitotoxicity

Correct Answer: Blocking voltage-gated Na+ channels at the outer pore and preventing Na+ entry

Q14. The delayed rectifier potassium current is carried by:

• Voltage-gated K+ channels responsible for repolarization
• Voltage-gated Na+ channels responsible for depolarization
• Ligand-gated Cl- channels
• Calcium-activated chloride channels only

Correct Answer: Voltage-gated K+ channels responsible for repolarization

Q15. The major role of the Na+/K+ ATPase (sodium pump) in neurons is to:

• Maintain ionic gradients (Na+ low inside, K+ high inside) essential for resting potential and APs
• Generate immediate action potentials by pumping Na+ inward
• Serve as the primary fast repolarizing current during an AP
• Directly release neurotransmitter into the synaptic cleft

Correct Answer: Maintain ionic gradients (Na+ low inside, K+ high inside) essential for resting potential and APs

Q16. The Goldman-Hodgkin-Katz (GHK) equation is used to:

• Calculate membrane potential considering multiple ions and their permeabilities
• Predict single-ion equilibrium potentials only
• Measure action potential frequency experimentally
• Determine the intracellular pH based on ion flux

Correct Answer: Calculate membrane potential considering multiple ions and their permeabilities

Q17. Hypokalemia (low extracellular K+) typically affects neuronal resting potential by:

• Hyperpolarizing the membrane and decreasing neuronal excitability
• Depolarizing the membrane and increasing excitability
• No change in resting membrane potential
• Causing immediate action potential firing

Correct Answer: Hyperpolarizing the membrane and decreasing neuronal excitability

Q18. Hyperkalemia (elevated extracellular K+) usually causes which initial effect on neurons?

• Depolarization of the resting membrane potential and increased excitability (initially)
• Hyperpolarization and decreased excitability
• Inactivation of the Na+/K+ pump only
• Immediate myelin formation

Correct Answer: Depolarization of the resting membrane potential and increased excitability (initially)

Q19. Lowering extracellular Ca2+ concentration typically changes neuronal excitability by:

• Reducing the threshold for action potentials and increasing excitability
• Increasing threshold and reducing excitability
• Directly blocking voltage-gated Na+ channels
• Inhibiting the Na+/K+ ATPase

Correct Answer: Reducing the threshold for action potentials and increasing excitability

Q20. Myelination increases conduction speed mainly by:

• Increasing membrane resistance and decreasing capacitance, enabling saltatory conduction
• Increasing membrane capacitance to store more charge
• Reducing axon diameter to speed current flow
• Blocking voltage-gated channels along the internode

Correct Answer: Increasing membrane resistance and decreasing capacitance, enabling saltatory conduction

Q21. Demyelination (e.g., multiple sclerosis) typically leads to:

• Slowed conduction velocity and possible conduction block
• Enhanced saltatory conduction and faster signaling
• Permanent closure of voltage-gated Na+ channels
• Increased membrane resistance improving signal fidelity

Correct Answer: Slowed conduction velocity and possible conduction block

Q22. The spike-initiation zone of most neurons is located at the:

• Axon hillock/axon initial segment because of high Na+ channel density
• Dendritic tips because they integrate inputs
• Soma because it contains most mitochondria
• Axon terminal because neurotransmitter release triggers APs

Correct Answer: Axon hillock/axon initial segment because of high Na+ channel density

Q23. Compared to unmyelinated axons, myelinated axons are more energy efficient because:

• Fewer ions cross the membrane per distance traveled, reducing pump workload
• They have continuously open Na+ channels along the entire axon
• They utilize Ca2+ currents instead of Na+ currents
• They do not require ATP for ion gradient maintenance

Correct Answer: Fewer ions cross the membrane per distance traveled, reducing pump workload

Q24. During the rising phase of an action potential, which ion predominantly moves into the neuron?

• Sodium (Na+)
• Potassium (K+)
• Chloride (Cl-)
• Magnesium (Mg2+)

Correct Answer: Sodium (Na+)

Q25. Which property best describes the inactivation gate behavior of voltage-gated Na+ channels?

• Fast inactivation during depolarization followed by slow recovery on repolarization
• Permanently open during the entire action potential
• Only sensitive to extracellular potassium levels
• Activates only after the absolute refractory period

Correct Answer: Fast inactivation during depolarization followed by slow recovery on repolarization

Q26. The amplitude of a single action potential in a healthy neuron is primarily determined by:

• Ionic gradients across the membrane and the all-or-none property (not stimulus strength)
• The strength of the initiating stimulus directly
• The number of synapses on the dendrites
• The color of the neuron under microscopy

Correct Answer: Ionic gradients across the membrane and the all-or-none property (not stimulus strength)

Q27. Refractory periods are physiologically important because they:

• Ensure unidirectional propagation of action potentials and limit firing frequency
• Allow continuous back-and-forth propagation along the axon
• Prevent neurotransmitter release at the synapse
• Increase membrane leak to ions permanently

Correct Answer: Ensure unidirectional propagation of action potentials and limit firing frequency

Q28. Which extracellular change tends to increase the threshold for action potential initiation?

• Increased extracellular Ca2+ concentration stabilizing Na+ channels
• Decreased extracellular Ca2+ concentration
• Increased extracellular K+ causing depolarization
• Lowering temperature to increase membrane fluidity

Correct Answer: Increased extracellular Ca2+ concentration stabilizing Na+ channels

Q29. Which pharmacological agent blocks voltage-gated K+ channels and can enhance neurotransmitter release or excitability?

• 4-Aminopyridine (4-AP)
• Lidocaine
• Propranolol
• Saxitoxin

Correct Answer: 4-Aminopyridine (4-AP)

Q30. Which property describes ‘use-dependent’ block of sodium channels by some drugs?

• Increased block with repetitive or sustained channel activation (e.g., lidocaine)
• Blocking only at resting membrane potentials
• Enhancing Na+ influx with use
• Binding only to closed channels and never to open channels

Correct Answer: Increased block with repetitive or sustained channel activation (e.g., lidocaine)

Q31. Compared to continuous conduction in an unmyelinated axon, saltatory conduction is characterized by:

• Faster propagation and reduced energy cost due to node-to-node jumping
• Slower conduction because of gaps between nodes
• AP amplitude gradually declining over distance
• Dependence on ligand-gated channels rather than voltage-gated channels

Correct Answer: Faster propagation and reduced energy cost due to node-to-node jumping

Q32. How does decreased temperature typically affect nerve conduction?

• It slows conduction velocity and can prolong action potential duration
• It accelerates action potential propagation
• It increases amplitude of action potentials indefinitely
• It has no effect on ion channel kinetics

Correct Answer: It slows conduction velocity and can prolong action potential duration

Q33. Patch-clamp electrophysiology is a technique primarily used to:

• Record currents through single ion channels or whole-cell currents
• Visualize myelin sheaths under light microscopy
• Measure extracellular neurotransmitter concentration only
• Directly measure ATP production in real time

Correct Answer: Record currents through single ion channels or whole-cell currents

Q34. The safety factor for conduction refers to:

• The ratio of current available to depolarize the next segment relative to the minimum required
• The number of synapses onto a neuron
• The maximal firing frequency of a neuron
• The amount of myelin covering an axon

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

Q35. In mature central neurons, opening of chloride-permeable GABA-A receptors typically causes:

• Cl- influx or stabilization leading to hyperpolarization and inhibition
• Sustained depolarization and excitation via Na+ entry
• Activation of voltage-gated calcium channels directly
• Rapid myelination of the dendrites

Correct Answer: Cl- influx or stabilization leading to hyperpolarization and inhibition

Q36. Which neuronal region typically has the highest density of voltage-gated Na+ channels for AP initiation?

• Axon initial segment (axon hillock)
• Dendritic shaft
• Soma center
• Presynaptic terminal exclusively

Correct Answer: Axon initial segment (axon hillock)

Q37. Demyelination reduces conduction safety factor because it:

• Decreases membrane resistance and increases current leak across internodes
• Increases nodal Na+ channel density to pathological levels
• Converts nodes into continuous myelin segments
• Directly inactivates the Na+/K+ ATPase

Correct Answer: Decreases membrane resistance and increases current leak across internodes

Q38. The Hodgkin-Huxley model of the action potential includes:

• Voltage-dependent conductances for Na+ and K+ described by gating variables
• Only ligand-gated currents and no voltage dependence
• Perfectly passive membrane behavior without active channels
• Direct representation of neurotransmitter release kinetics

Correct Answer: Voltage-dependent conductances for Na+ and K+ described by gating variables

Q39. The Na+/K+ ATPase exchanges ions in what stoichiometry per ATP hydrolyzed?

• 3 Na+ exported for 2 K+ imported per ATP
• 1 Na+ exported for 1 K+ imported per ATP
• 2 Na+ exported for 3 K+ imported per ATP
• No ions are moved; it only binds ATP

Correct Answer: 3 Na+ exported for 2 K+ imported per ATP

Q40. During the absolute refractory period sodium channels are in which functional state?

• Inactivated and unable to open even with depolarization
• Fully closed but ready to open immediately
• Permanently nonfunctional and degraded
• Open and conducting maximal Na+ current

Correct Answer: Inactivated and unable to open even with depolarization

Q41. A delayed afterdepolarization (DAD) following an action potential is often due to:

• Excess intracellular Ca2+ causing transient inward currents (e.g., via Na+/Ca2+ exchange)
• Immediate opening of large K+ conductance to hyperpolarize the membrane
• Rapid activation of myelin synthesis
• Inactivation of all Na+ channels permanently

Correct Answer: Excess intracellular Ca2+ causing transient inward currents (e.g., via Na+/Ca2+ exchange)

Q42. Action potential propagation in a healthy axon is described as non-decremental, meaning:

• The amplitude of the AP does not diminish as it travels along the axon
• AP amplitude steadily declines and disappears with distance
• Each successive AP is smaller than the previous one
• Propagation depends solely on gap junctions

Correct Answer: The amplitude of the AP does not diminish as it travels along the axon

Q43. Which factor increases the electrotonic length constant (lambda) and favors longer passive spread of depolarization?

• Increased membrane resistance (e.g., myelination)
• Increased membrane capacitance only
• Smaller axon radius
• Higher cytoplasmic resistivity

Correct Answer: Increased membrane resistance (e.g., myelination)

Q44. Myelination reduces the membrane time constant (tau) mainly because it:

• Decreases membrane capacitance (Cm), allowing faster charging of the membrane
• Greatly increases the membrane capacitance
• Eliminates voltage-gated channels at nodes
• Directly reduces sodium gradient across the membrane

Correct Answer: Decreases membrane capacitance (Cm), allowing faster charging of the membrane

Q45. Saxitoxin, a marine toxin, acts on neurons by:

• Blocking voltage-gated Na+ channels similarly to tetrodotoxin
• Opening voltage-gated K+ channels to hyperpolarize cells
• Inhibiting acetylcholinesterase at synapses
• Stimulating excessive myelin production

Correct Answer: Blocking voltage-gated Na+ channels similarly to tetrodotoxin

Q46. A hereditary mutation in voltage-gated Na+ channels causing neuronal hyperexcitability and seizures is best classified as a:

• Channelopathy affecting sodium channel function
• Defect in the Na+/K+ ATPase gene only
• Primary myelination disorder without channel involvement
• Mutation that exclusively affects chloride channels

Correct Answer: Channelopathy affecting sodium channel function

Q47. Excitatory postsynaptic potentials (EPSPs) typically depolarize the postsynaptic membrane by:

• Opening cation channels (e.g., Na+ influx) making the membrane more positive
• Opening chloride channels causing hyperpolarization
• Directly activating the Na+/K+ pump to hyperpolarize
• Increasing extracellular potassium to hyperpolarize the cell

Correct Answer: Opening cation channels (e.g., Na+ influx) making the membrane more positive

Q48. A compound action potential recorded from a nerve bundle represents:

• The summed electrical activity of multiple axons with different conduction velocities
• A single uniform action potential from one axon only
• Only the activity of motor fibers excluding sensory fibers
• Direct measurement of synaptic vesicle release

Correct Answer: The summed electrical activity of multiple axons with different conduction velocities

Q49. Nodes of Ranvier are rich in which of the following to support saltatory conduction?

• Voltage-gated Na+ channels concentrated at the nodal membrane
• Lipid-rich myelin layers preventing ion flow at the node
• High density of ligand-gated K+ channels only
• Exclusively mitochondria and no ion channels

Correct Answer: Voltage-gated Na+ channels concentrated at the nodal membrane

Q50. Saltatory conduction improves conduction efficacy primarily because:

• The action potential is regenerated only at nodes of Ranvier, reducing ionic leak and energy cost
• Action potentials are generated continuously along the internode
• It eliminates the need for voltage-gated channels entirely
• It increases the number of synapses required for signal transmission

Correct Answer: The action potential is regenerated only at nodes of Ranvier, reducing ionic leak and energy 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.

Mail- Sachin@pharmacyfreak.com