The sodium-potassium pump actively transports three sodium ions ($$Na^+$$) out of the cell for every two potassium ions ($$K^+$$) it brings in. Because it removes more positive charges than it brings in, this pump creates a net negative charge inside the cell.

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In the resting state, the inside of a cell is slightly negatively charged compared to the outside. This net negative charge is primarily due to the activity of the sodium-potassium pump.

Cell Resting State Net Charge

The sodium-potassium pump is an active transport protein in the plasma membrane that is crucial for maintaining a cell's resting potential. It moves ions against their concentration gradients by breaking down ATP into ADP for energy. Specifically, the pump expels sodium ions (Na+) from the cytoplasm to the extracellular fluid, where their concentration is higher, and imports potassium ions (K+) from the extracellular fluid into the cytoplasm. In neurons, this unequal exchange expels three positively charged sodium ions for every two positively charged potassium ions it brings in, creating a net negative charge inside the cell.

Sodium-Potassium Pump

Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020, April 22). Psychology (2nd ed.). OpenStax. https://openstax.org/books/psychology-2e/pages/1-introduction

OpenStax Psychology (2nd ed.) Textbook

Sodium-Potassium Pump Mechanism

During the cell's resting state, sodium ($$Na^+$$) is at a higher concentration outside the cell than inside. This concentration gradient, along with the net negative charge inside the cell, creates a force that tends to move sodium into the cell.

Resting State Sodium Concentration

In the resting state, potassium ($$K^+$$) is more concentrated inside the cell than outside. Due to this concentration gradient, potassium tends to move out of the cell.

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