[Na+] inside vs outside

[Na+] inside vs outside

• A. Higher on inside
• B. Lower on inside
• C. Equal on both sides
• D. Absent on inside

Answer: (B)

Sodium concentration is much higher outside the cell than inside. In most mammalian cells, extracellular Na+ is about 140 mM while intracellular Na+ is around 10 mM. This gradient is actively maintained by the Na+/K+ ATPase, which pumps Na+ out of the cell and K+ in, using ATP. That gradient is the driving force for Na+ to enter the cell during events like depolarization, via voltage-gated Na+ channels, contributing to action potentials. Because the inside concentration is kept low, the correct description is that Na+ is lower inside than outside.

Sodium concentration is much higher outside the cell than inside. In most mammalian cells, extracellular Na+ is about 140 mM while intracellular Na+ is around 10 mM. This gradient is actively maintained by the Na+/K+ ATPase, which pumps Na+ out of the cell and K+ in, using ATP. That gradient is the driving force for Na+ to enter the cell during events like depolarization, via voltage-gated Na+ channels, contributing to action potentials. Because the inside concentration is kept low, the correct description is that Na+ is lower inside than outside.