What Do Electrolytes Actually Do?

Sports drink commercials love talking about them, but what are electrolytes, why do we need them, and what happens if we don’t have enough? Electrolytes are salts that, once in our bodies, help our cells move water around. They also enable the nerve impulses that keep our hearts beating, our lungs breathing and our brains learning. But we can also lose them — for example, by sweating. Given all the ins and outs of electrolytes, should you reach for that bright orange sports drink after running around the block?