What’s the function of sodium in the body?

• A. Provides energy to cells
• B. Helps maintain fluid balance, transmission of nerve impulses, influences contraction and relaxation of muscles
• C. Stores vitamins
• D. Builds bones

Answer: (B)

Sodium’s job is to keep body fluids properly balanced and to support electrical signals in the body. It’s the main extracellular cation, so its concentration helps control osmolality and fluid volume across compartments. This gradient also powers nerve impulses: when nerves fire, sodium rushes into cells during depolarization, starting an action potential that carries the signal along the nerve. That same electrical activity governs muscle contraction, and the sodium–potassium pump then helps reset ion balances so muscles can relax after contracting. The other options aren’t correct because energy for cells comes from ATP produced from carbohydrates, fats, and proteins; sodium doesn’t store vitamins or build bones.