The mineral found in table salt that is essential for nerve and muscle function but harmful in excess is sodium.
Table salt is mainly sodium chloride (NaCl), an ionic compound made from sodium and chloride ions. Sodium acts as an electrolyte: differences in sodium concentration across cell membranes help generate nerve impulses and trigger muscle contraction. It also helps regulate fluid balance, blood volume, and blood pressure.
The common mix-up is confusing sodium with salt. Salt contains sodium, but they are not identical: table salt is about 39% sodium by weight. Other foods and additives, including processed meals, sauces, baking soda, and monosodium glutamate, can also contribute sodium.
The body needs sodium in small amounts, but consistently high intake can raise blood pressure and increase cardiovascular risk. Potassium is a different electrolyte with many related roles, while zinc and iron are essential minerals involved in immunity, enzymes, and oxygen transport rather than the primary nerve-signaling role described here.