During the rising phase of an action potential

Correct option is A

During the rising phase of an action potential, sodium (Na+) ions rush into the cell through voltage-gated sodium channels. This influx of positively charged ions causes the membrane potential to become more positive (i.e., depolarization). This is the initial part of the action potential, which ultimately leads to the cell reaching its peak potential.

Information Booster:
1. The rising phase is caused by the opening of sodium channels, leading to rapid depolarization.
2. Potassium (K+) ions exit the cell later, during the falling phase, to restore the resting potential.
3. Chloride (Cl-) ions play a role in inhibitory postsynaptic potentials (IPSPs) but not in action potentials.
4. The rising phase is essential for nerve signal transmission along neurons.