How hearing works. When these sound waves reach the ear, they travel down the ear canal and hit the eardrum, making it vibrate. Three tiny bones in the middle ear link the vibrating eardrum to a tiny bone structure in the inner ear called the cochlea. The cochlea is filled with liquid that carries the vibrations to thousands of tiny hair cells. The movement in the fluid causes the cells to carry a message to the nerve that is connected to the brain, which turns the signals into what you hear.