Question

During the propagation of a nerve impulse, the action potential results from the movement of ______.

• A. K⁺ ion from extracellular fluid to intracellular fluid
• B. K⁺ ions from intracellular fluid to extracellular fluid
• C. Na⁺ ions from extracellular fluid to intracellular fluid
• D. Na⁺ ions from intracellular fluid to extracellular fluid

Answer 1

The correct option is C

Na⁺ ions from extracellular fluid to intracellular fluid

Once an action potential has started, it moves (propagated) along an axon automatically. When a stimulus is applied at a site on the polarised membrane, the membrane at the site becomes freely permeable to Na⁺. This leads to a rapid influx of Na⁺ from the extracellular fluid to intracellular fluid, followed by the reversal of the polarity at that site, i.e., the outer surface of the membrane becomes negatively charged and the inner side becomes positively charged. The polarity of the membrane at the site is thus reversed and hence depolarised. The electrical potential difference across the plasma membrane at a particular site is called the action potential, which is in fact termed as a nerve impulse.