The smallest bone in the human body sits inside the ear and helps hearing.

The longer version

Inside the middle ear sits a chain of three tiny bones that carry vibration from the eardrum to the fluid-filled inner ear. The last and smallest of them presses against a membrane leading into the cochlea.

Because sound has to move from air into liquid, the chain acts as a mechanical amplifier: the eardrum collects vibration over a wide area and concentrates it onto a much smaller one, which raises the pressure enough to push the fluid. Without that conversion, most sound energy would simply bounce off. The bones are among the few parts of the skeleton that reach full size early in life.

Where this entry sits

These facts look at how the human body works in ordinary moments, from breathing and blinking to balance and sleep. They focus on anatomy, senses, and small reactions that happen constantly without any conscious effort. The full list sits on the Human Body page, where every entry is listed in order.