Action Potential & Excitability — Cellular & General Physiology

Action Potential & Excitability MCQs: practice questions

Sample Action Potential & Excitability multiple-choice questions from Cellular & General Physiology.

1. Threshold is the membrane potential at which:

   • A. The cell can never fire
   • B. K+ equilibrium is reached
   • C. All channels close
   • D. The membrane becomes impermeable
   • E. An action potential becomes inevitable

2. Which statement best distinguishes absolute from relative refractoriness?

   • A. Both are completely resistant to stimulation
   • B. Only the absolute period requires K+ channels
   • C. Only the relative period permits an action potential with a sufficiently strong stimulus
   • D. The absolute period occurs after the relative period
   • E. The relative period occurs before depolarization

3. If extracellular Na+ concentration is markedly reduced, the amplitude of a nerve action potential would most likely:

   • A. Increase
   • B. Remain identical in all circumstances
   • C. Decrease
   • D. Reverse the K+ gradient
   • E. Eliminate the resting potential only

4. A local anesthetic blocks voltage-gated Na+ channels in a peripheral nerve. The immediate electrophysiologic effect is:

   • A. Increased action-potential amplitude
   • B. Increased neurotransmitter synthesis
   • C. Faster K+ accumulation inside the cell
   • D. Failure of action-potential initiation or propagation
   • E. Prolonged Na+ channel opening

5. TEA reduces action-potential repolarization by blocking:

   • A. GABAA receptors
   • B. Voltage-gated Na+ channels
   • C. Na+–glucose cotransporters
   • D. Voltage-gated K+ channels
   • E. Na+–K+ pumps

6. A voltage-gated Na+ channel has its activation gate open but its inactivation gate closed. The channel is:

7. Myelination increases conduction velocity by:

8. A toxin prevents Na+ channel inactivation but leaves activation intact. Which phase would most directly be prolonged?

9. A neuron is stimulated below threshold. What is the expected result?

10. A skeletal muscle membrane is chronically depolarized by severe hyperkalemia and fails to fire despite being closer to threshold. This is an example of:

11. A demyelinating lesion slows conduction because it primarily disrupts:

12. Which process is primarily responsible for repolarization of a nerve action potential?

13. Depolarization means that the membrane potential becomes:

14. Depolarization rapidly increases Na+ conductance because it:

15. An inward current is defined as movement of:

16. The peak of an action potential briefly becomes positive to 0 mV. This portion is called the:

17. Which feature makes an action potential propagate without progressively decreasing in amplitude?

18. Which event restores Na+ channels from the inactivated state to a closed, activatable state?

19. Increasing axon diameter increases conduction velocity primarily because it:

20. If voltage-gated K+ channels opened earlier than usual during a nerve action potential, the likely effect would be:

21. Which property is characteristic of an action potential?

22. Which agent listed in the source also blocks voltage-sensitive Na+ channels and can abolish action potentials?

23. The relative refractory period begins:

24. The absolute refractory period is the interval during which:

25. During the upstroke of a nerve action potential, the major ionic current is:

26. During the undershoot, the membrane potential approaches:

27. The absolute refractory period occurs largely because:

28. Tetrodotoxin abolishes nerve action potentials mainly by blocking:

29. Action-potential propagation along an unmyelinated axon depends on:

30. Why is a stronger stimulus needed during the relative refractory period?