Biology - Neural Control and Coordination Question with Solution | TestHub

During the resting state, the concentration of ${\text{Na}}^{+}$ is high in the extracellular fluid and low in the intracellular fluid.

When a nerve fibre is stimulated, voltage-gated ${\text{Na}}^{+}$ channels open, making the membrane highly permeable to ${\text{Na}}^{+}$ ions.

This causes a rapid influx of ${\text{Na}}^{+}$ ions from the extracellular fluid into the intracellular fluid down their concentration gradient.

The influx of positive charges reverses the polarity of the membrane, causing depolarization, which generates the action potential.

Answer: ${\text{Na}}^{+}$ ions from extracellular fluid to intracellular fluid.