Muscles, bones, and the brain. Three vital elements to blink, nod, walk, or run. The brain gives the orders, the muscles activate the bones that make the skeleton. So, what's the use of the skeleton? It's the body's frame, it's the one allowing humans to stand, for example. Over time, the skeleton evolved with the brain to meet its needs. Therefore, humans and monkeys are the only ones owing a thumb that allows them to catch stuff and use tools! And how does the skeleton move? Thanks to the joints, ligaments, tendons, and muscles!