Which ion concentration is higher outside the cell compared to inside?

In a typical resting cell, the concentration of sodium ions (Na+) is significantly higher outside the cell than inside. This difference in concentration is primarily maintained by the sodium-potassium pump, which actively transports sodium out of the cell while moving potassium (K+) into the cell. The extracellular fluid has a Na+ concentration ranging from approximately 135 to 145 mEq/L, whereas the intracellular concentration is much lower, typically around 10 to 15 mEq/L.

This sodium gradient is essential for various physiological processes, including the generation of action potentials in neurons and muscle cells. When a cell is stimulated, sodium channels open, allowing Na+ to flow into the cell, leading to depolarization and the propagation of an electrical signal.

In contrast, other ions like potassium (K+), calcium (Ca2+), and chloride (Cl-) have different distribution patterns. Potassium is typically higher inside the cell, calcium is generally very low inside the cell with higher concentrations outside, and chloride concentrations can vary but are often higher in the extracellular fluid than inside. Understanding these ion gradients is crucial in physiology and cell biology, as they play significant roles in cellular function and communication.