Question

During transmission of a nerve impulse, the action potential results from the movement of---------.

• A. \(\text{K}^{+}\) ions from extracellular fluid to intracellular fluid.
• B. \(\text{Na}^{+}\) ions from intracellular fluid to extracellular fluid.
• C. \(\text{K}^{+}\) ions from intracellular fluid to extracellular fluid.
• D. \(\text{Na}^{+}\) ions from extracellular fluid to intracellular fluid.

Hint:

An action potential starts when sodium ions rush from outside the axon to inside.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept
At rest the axon membrane is polarised, with the inside negative and more sodium outside.

Step 2: On stimulation
Voltage-gated sodium channels open and sodium ions move from the extracellular fluid into the axoplasm.
The inside becomes positive, which is depolarisation, and this is the action potential.

Step 3: Later events
Outflow of potassium ions only restores the resting state (repolarisation).

Step 4: Conclusion
The action potential results from sodium ions moving from extracellular to intracellular fluid.

Final Answer:
Sodium ions move from outside to inside the neuron. \[ \boxed{\text{(D) }\text{Na}^{+}\text{ ions from extracellular fluid to intracellular fluid.}} \]