MCQ Quiz

Q1. The resting membrane potential of a typical peripheral nerve fiber is mainly determined by:

Sodium equilibrium potential

Potassium equilibrium potential

Calcium permeability

Chloride influx

Explanation:
Resting membrane potential (~ −65 mV) is closest to potassium equilibrium potential (−90 mV), as the membrane is most permeable to K⁺ at rest.

Q2. Which ionic movement is primarily responsible for the depolarization phase of the action potential?

Potassium efflux

Calcium influx

Sodium influx

Chloride influx

Explanation:
Depolarization occurs due to opening of voltage-gated Na⁺ channels and rapid sodium influx.

Q3. During which phase of the action potential is the nerve completely unexcitable regardless of stimulus strength?

Depolarization

Repolarization

Relative refractory period

Absolute refractory period

Explanation:
During the absolute refractory period, Na⁺ channels are inactivated and threshold is effectively infinite.

Q4. Saltatory conduction occurs because depolarization happens mainly at:

Nodes of Ranvier

Myelin sheath

Axon hillock

Schwann cell cytoplasm

Explanation:
Myelin is impermeable to ions, so action potentials are regenerated only at nodes of Ranvier.

Q5. Which statement regarding myelinated nerve fibers is CORRECT?

They conduct impulses continuously

They are faster and more energy efficient

They show decremental conduction

Ion exchange occurs along the entire axon

Explanation:
Saltatory conduction allows faster transmission with less ion exchange and lower energy consumption.

Q6. Antidromic conduction is MOST clearly demonstrated in:

Motor nerve stimulation at the spinal cord

Sensory transmission to CNS

Axon reflex in the skin

Normal voluntary muscle contraction

Explanation:
In axon reflex, impulses travel antidromically toward arterioles causing vasodilation.

Q7. Synaptic transmission is unidirectional mainly because of:

Localization of neurotransmitter receptors on the postsynaptic membrane

Higher sodium concentration in synaptic cleft

Calcium influx in postsynaptic neuron

Electrical resistance of synapse

Explanation:
Neurotransmitter vesicles are presynaptic, while receptors are postsynaptic.

Q8. The synaptic delay of about 0.5 ms is mainly due to:

Diffusion of sodium ions

Action potential propagation

Postsynaptic depolarization

Neurotransmitter release and binding

Explanation:
Chemical steps of calcium entry, vesicle fusion, and receptor binding cause synaptic delay.

Q9. Synaptic transmission is enhanced by:

Acidosis

Alkalosis

Hypoxia

Hypercapnia

Explanation:
Alkalosis increases neuronal excitability and synaptic transmission.

Q10. Which nerve fiber type conducts fast pain?

Aα

Aβ

C fibers

Aδ fibers

Explanation:
Aδ fibers are thinly myelinated and transmit fast, sharp pain.

Q11. Which fibers are MOST resistant to pressure?

C

B

A

All equally

Explanation:
Pressure blocks large myelinated fibers last (A > B > C).

Q12. A decrease in nerve conduction velocity MOST strongly suggests:

Demyelination

Axonal hypertrophy

Increased fiber diameter

Hypercalcemia

Explanation:
Myelin loss slows impulse conduction significantly.

Q13. The peak of the compound action potential represents activity of:

Slowest fibers

Largest diameter fibers

Unmyelinated fibers

Autonomic fibers

Explanation:
Large fibers conduct fastest and contribute to the earliest, highest CAP peak.

Q14. Increasing stimulus strength above maximal stimulus causes:

Larger action potentials

Faster conduction velocity

More depolarization per axon

No increase in CAP amplitude

Explanation:
Once all axons are recruited, CAP amplitude cannot increase further.

Q15. Hypocalcemia increases nerve excitability primarily by:

Lowering threshold for sodium channel opening

Blocking potassium channels

Increasing chloride conductance

Reducing membrane permeability

Explanation:
Low calcium allows Na⁺ channels to open with minimal depolarization.

Q16. Carpopedal spasm is a clinical feature of:

Hyperkalemia

Hypercalcemia

Hypocalcemia

Acidosis

Explanation:
Hypocalcemia causes spontaneous nerve firing and tetany.

Q17. Which type of nerve injury has the BEST prognosis for regeneration?

Neurotmesis

Axonotmesis

Complete transection

Fibrosis

Explanation:
In axonotmesis, Schwann cells remain intact, allowing regeneration.

Q18. Distal nerve degeneration after injury occurs mainly because of:

Ischemia

Inflammation

Immune attack

Loss of neurotrophic support

Explanation:
Loss of trophic substances from the cell body leads to Wallerian degeneration.

Q19. Neurotrophins are transported to the neuronal cell body mainly by:

Retrograde axonal transport

Anterograde transport

Passive diffusion

Blood circulation

Explanation:
Target-derived neurotrophins move retrogradely to support neuron survival.

Q20. The earliest event in peripheral nerve regeneration is:

Reinnervation of muscle

Remyelination

Formation of axonal sprouts