How do we hear?

When you hit a table with a spoon, you hear the noise it makes quite clearly. And you also feel the spoon vibrating. But you may not realise that the noise is really made of those same sorts of vibrations, called sound waves in the air, which enable us to hear the noise.

The part of the ear on the outer side of the head does very little to help us hear. But inside the ear are the delicate organs which actually do the work. The first of these is a thin skin, stretched tightly across a tube. This skin is called the ear drum. Behind it are three delicate little bones called the anvil, the hammer and the stirrup. When sound waves touch the ear drum it vibrates and makes these three tiny bones vibrate too. The bones are attached to the shell-shaped inner ear organs called the cochlea, and the bones’ vibration set up others in the fluid in the cochlea. Tiny cells here turn the sound waves into messages which the ear’s main nerve takes to the brain, where the sounds are identified and recognized. Also in the inner ear are three other organs called the semi circular canals, which control our sense of balance. If anything should go wrong with this part of the ear, we become dizzy and cannot balance properly.