Ques. 1AIPMT 2008
During the propagation of a nerve impulse, the action potential results from the movement of
- K+ ions from intracellular fluid to extracellular fluid
- Na+ ions from extracellular fluid to intracellular fluid
- K+ ions from extracellular fluid to intracellular fluid
- Na+ ions from intracellular fluid to extracellular fluid
Answer
(2) Na+ ions from extracellular fluid to intracellular fluid
Solution
As per NCERT, when a stimulus is applied, the membrane at that site becomes freely permeable to Na+.
This leads to a rapid influx of Na+ from the extracellular fluid into the axon (intracellular fluid), so the polarity at that site reverses (inside positive, outside negative); this depolarised state is the action potential, i.e., the nerve impulse.
The outflow of K+ occurs later and restores the resting potential (repolarisation).
Answer: (2)