Final answer:
The sodium-potassium pump is the primary contributor to maintaining the neuron's resting membrane potential, creating a negative charge inside the cell by actively transporting sodium out and potassium in.
Step-by-step explanation:
The key contributor to the maintenance of the resting membrane potential in neurons is the sodium-potassium pump. This pump uses energy from ATP to exchange ions across the neuron's cell membrane, expelling three sodium ions (Na+) for every two potassium ions (K+) it brings in. This activity contributes to a higher concentration of potassium inside the cell and a higher concentration of sodium outside the cell. Consequently, the inside of the neuron becomes negatively charged relative to the outside. Potassium ions also play a key role, as they are more permeable and can move out of the cell more freely through potassium leakage channels, which helps maintain the negative charge inside the cell necessary for the resting potential.