How your ear works - Inside the Human Body: Building Your Brain - BBC One

Inside your ear, sounds set off a complex chain of events. They enter as pressure waves, which push and pull your eardrum, making it vibrate. On the other side of the eardrum, these vibrations set a series of bones jiggling. They end with the smallest bone in your entire body, called the sternum. It is smaller than a grain of rice. These bones allow you to hear. If a sound is too loud, a muscle pulls the stirrup away from the most sensitive parts. Temporarily, at least, you go a bit deaf, but the rest of your ear is protected. Beyond the stirrup is a fluid-filled cavity, air-like sensors on the floor. These begin to dance to the sounds of the world outside. You have 30,000 sensors. Each picks out a different part of the sound and sends it straight to your brain.