Final answer:
Excess K+ built up inside a resting neuron would lead to hyperpolarization, making the neuron's interior more negative and moving the cell further away from reaching its action potential threshold.
Step-by-step explanation:
The student has asked whether excess K+ (potassium ions) built up inside a resting neuron would (a) hyperpolarize, (b) depolarize, (c) facilitate, or (d) more than one of the above. When K+ ions accumulate inside a neuron, they tend to move out of the cell, helping to establish a negative resting membrane potential. However, if they are in excess inside the neuron and cannot leave because potassium channels are closed or if more potassium stays inside than it should, it prevents repolarization or even leads to hyperpolarization ensuring the membrane potential becomes even more negative than the normal resting potential. This movement of K+ away from the cell interior contributes to hyperpolarization, not depolarization. Depolarization is primarily associated with Na+ (sodium ions) entering the neuron.
Upon reaching the threshold of excitation, the neuron fires an action potential; this is marked by a wave of depolarization followed by repolarization and slightly overshooting to a hyperpolarized state before returning to the resting potential. The answer to the question, therefore, is (a) hyperpolarize.