Earbuds are basically a tiny pair of speakers that go inside the ears. They're fine
at low volumes, but they can cause permanent hearing loss if not used properly. Find
out what's safe (and not) in this article for teens.
If the brain is a central computer that controls all the functions of the body, then
the nervous system is like a network that relays messages back and forth to different
parts of the body. Find out how they work in this Body Basics article.