Final answer:
The membrane potential will depolarize by the greatest amount if the membrane permeability increases for sodium (Na+), as this will cause a rapid influx of positive ions into the neuron, resulting in depolarization.
Step-by-step explanation:
The membrane potential of a neuron will depolarize by the greatest amount if the membrane permeability increases for sodium (Na+). During depolarization, Na+ channels open, allowing Na+ ions to rush into the cell due to a strong concentration gradient and the Coulomb force created by the negative proteins below the membrane.
This influx of sodium ions causes the inside of the membrane to become less negative and ultimately positive, reaching up to +30 mV, which is a significant change from the resting potential of around -70 mV. In contrast, potassium (K+) and chloride (Cl-) ions are not as effective in creating a large depolarization when their permeability increases.
For instance, while K+ does leave the cell during repolarization, it is actually working to bring the membrane potential back toward the negative, resting voltage. Similarly, Cl- ions entering the cell would also tend to hyperpolarize the membrane, making it more negative, rather than depolarizing it.
Therefore, an increase in sodium permeability has the most profound effect on membrane potential because it directly leads to a rapid depolarization phase, which is an essential step for the generation of an action potential in neurons.