How do we hear?

Ears appear to be quite simple structures but are actually parts of a complex system made up of passages, structures that vibrate, nerves and specialised areas of the brain that are all working together to gather and process the sounds we hear around us.

The ear is made up of three parts: the outer ear, middle ear and inner ear.  How these three parts work together enable us to receive and process sound waves that can be turned into electrical impulses that are transmitted to the brain.

Outer ear

The outer ear is made up of the visible part of the ear called the pinna, the ear canal (meatus) and the eardrum (tympanic membrane). The pinna is shaped a bit like a shell and gathers sound waves and directs them into the ear canal. When a sound wave strikes the eardrum, the eardrum vibrates.

Middle ear

Ear AnatomicalThe middle ear is an air-filled chamber that contains three tiny bones: the hammer (malleus)
which is attached to the eardrum, anvil (incus) which is in the middle of the three bones and stirrup (stapes) which is attached to the oval window – a membrane covered opening to the inner ear. This chamber is connected to the upper part of your throat by a narrow channel called the eustachian tube. The tube opens and closes as you swallow and helps to drain any fluids that may have built up and equalise pressure in the ear (which is why swallowing in the pressurised cabin of an aeroplane makes that ‘blocked up’ feeling in your ears go away). Having equal pressure on both sides of the eardrum is important for normal vibration of the eardrum.

When your eardrum vibrates, it triggers a chain of vibrations through each of the three bones. Because of differences in the size of the ear drum and entry to the inner ear and size and shape of the bones, the force of the vibration is increased by nearly 20 times when it reaches the inner ear. This increase in force is necessary to transfer the energy of the sound waves to the fluid of the inner ear.

Inner ear

The inner ear contains a group of fluid-filled chambers that are all interconnected. The chamber that is shaped like a snail is called the cochlea and sound vibrations from the bones of the middle ear are transferred to the fluids of the cochlea. Tiny ‘hair cells’ that line the inside of the cochlea convert the vibrations into electrical impulses that are transmitted along the auditory nerve to your brain.

The other fluid-filled chambers of the inner ear include three tubes called the semicircular canals and special sensors inside them help regulate your sense of balance.