Copyright © 2007 Dorling Kindersley
The ear is the organ of hearing and balance. The outer ear collects sound and directs it to the sensory structures deep inside the skull.
Sound travels into the ear as vibrations in air. The eardrum picks up the vibrations and transmits them to tiny bones in the middle ear. These bones pass the vibrations to the fluid-filled inner ear and the cochlea.
Sound vibrations travel along the cochlea’s spiral, fluid-filled tube, creating waves of pressure. These stimulate tiny hair cells on a structure called the organ of Corti, which sends signals to the brain.
The semicircular canals contain fluid that moves whenever the head moves, making tiny blobs of jelly swing and sway and triggering nerve cells. There are also two fluid-filled chambers, called the utricle and saccule, which contain blobs of jelly that sway with gravity, telling the brain which way is up and down.