Final answer:
The resting membrane potential is maintained by high extracellular sodium levels and a negative internal charge relative to the outside, with the cell membrane being more permeable to potassium than sodium. The sodium-potassium pump actively maintains this potential using ATP to transport ions against their concentration gradients.
Step-by-step explanation:
In the maintenance of the cell resting membrane potential, it is true that extracellular sodium levels are high and the inside of the cell is negative relative to its outside. The membrane's selective permeability allows for a high concentration of K+ inside the cell versus outside and a higher concentration of Na+ outside the cell than inside. This imbalance contributes to the resting membrane potential. However, while the membrane is more permeable to K+ ions because there are more potassium leakage channels, the sodium-potassium pump actively moves three Na+ ions out of the cell and two K+ ions into the cell against their concentration gradients, contributing to the negative charge inside the cell. This process consumes ATP and is an example of active transport. Hence, the steady state involves both passive and active processes.