What are the functions of sodium ions?

Sodium ions are involved in various important functions in biology. Sodium ions are  extracellular cations which are necessary for producing action potentials in both cardiac and nervous tissue. These ions are found higher in number outside of the cell, resulting in the negative charge in the resting membrane potential. When a neuron is stimulated enough to reach its threshold, voltage-gated sodium channels open in response in order to depolarize the membrane. The flooding of sodium ions assists in the rising phase of the action potential of neurons; more sodium channels are opened as the action potential moves throughout the neuron’s axon. Sodium ions are also responsible for maintaining the proper amount and distribution of water in the body. Sodium is the major cation of extracellular fluids, and the concentration of sodium ions is high compared to the concentration in most cells. This concentration gradient forms an osmotic pressure which expels water out of cells. Sodium is the only cation that is able to induce enough osmotic pressure for water to exit cells. Thus, sodium ions assist in the osmoregulation of water between intracellular and extracellular regions of the cell.