What causes a neuron to maintain a negative resting membrane potential?

A neuron maintains a negative resting membrane potential primarily due to its high permeability to potassium ions (K+) and low permeability to sodium ions (Na+). At rest, the neuronal membrane is significantly more permeable to K+ than Na+, allowing K+ to flow out of the cell. This efflux of positively charged K+ ions results in a net negative charge inside the neuron compared to the outside environment.

Additionally, the Na+/K+ pump contributes to this potential by actively transporting three Na+ ions out of the neuron for every two K+ ions it brings in. However, the resting state is predominantly determined by the relative permeability of the membrane to these ions. Since K+ channels are more open than Na+ channels at rest, more positive charges leave the neuron, reinforcing the negative internal environment.

The combination of high K+ permeability and low Na+ permeability is essential for establishing and maintaining the typical resting membrane potential, which is generally around -70 mV. This critical balance is what enables neurons to be ready for action potentials and transmission of signals when appropriately stimulated.