The three main sections of the ear

The ear is made up of three different parts - the outer ear, the middle ear and the inner ear.

The outer ear is made up of the pinna, a flesh covered cartilage appendage that can be seen on either side of the head, and the ear canal, which is about 2cm long. These structures receive and direct sound waves to the eardrum. When sound goes through the outer ear it is still a mechanical wave, an oscillating pattern of high and low pressure states.

The middle ear is a cavity filled with air that contains the eardrum, a tightly stretched membrane at the edge of the outer and middle ear, and three very small bones - the hammer, anvil and stirrup. When sound waves reach the ear drum, compression pushes it inward and rarefaction pushes it outward, causing it to vibrate at the same frequency as the sound waves. This mechanical vibration then causes the hammer, the anvil and the stirrup to vibrate at the same frequency. Because of the way these bones are organised, the vibration in the stirrup is greater than that of the hammer. Also, pressure waves coming into contact with the relatively large eardrum is concentrated as it is transformed into internal vibrations of the bones so that the force vibrating the stirrup is around fifteen times stronger. In these ways, the three small bones in the middle ear are able to amplify the vibrations of the sound waves.

The inner ear is made up of a cochlea, a small organ shaped a bit like a snail, the semi-circular canals, and the auditory nerve. The cochlea is filled with fluid and its inner surface is lined with over 20 000 hair-like nerve cells which play one of the most important parts in our ability to hear.  As the stirrup is connected to the inner ear, vibrations travel from it to the fluid of the inner ear and transform into compression waves which then bend the hair-like nerve cells, causing most of them (the outer ones) to tremble and shake. This makes the vibrations stronger and stronger. This increased vibration causes the remaining (inner) hair cells to release an electrical impulse that is sent via the auditory nerve to the brain. The brain is then capable of making sense of these nerve impulses and of interpreting what has been heard.