* Sodium-Potassium Pump: This active transport protein uses energy (ATP) to pump 3 sodium ions (Na+) out of the cell for every 2 potassium ions (K+) pumped into the cell. This creates an uneven distribution of ions across the membrane, with a higher concentration of Na+ outside the cell and a higher concentration of K+ inside the cell.
* Membrane Permeability: The cell membrane is more permeable to potassium ions (K+) than sodium ions (Na+). This means that potassium ions can more easily diffuse across the membrane down their concentration gradient, moving from inside the cell to the outside.
* Electrochemical Gradient: The combined effect of the concentration gradient and the electrical gradient (due to the difference in charge across the membrane) leads to a net movement of potassium ions out of the cell. This outflow of positive charge creates a negative charge inside the cell.
In summary: The resting membrane potential is established by the unequal distribution of sodium and potassium ions across the cell membrane, driven by the sodium-potassium pump and the membrane's selective permeability to potassium. This results in a slightly negative charge inside the cell, typically around -70 millivolts (mV).
