The outer ear consists of the pinna, which is the part you can see on the side of your head, and the external ear canal. Sound waves (vibrations) are gathered by the pinna and travel down the external ear canal until they reach the eardrum, causing it to vibrate.
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The middle ear is an air-filled space behind the eardrum that contains a chain of tiny bones called the ossicles (the malleus, incus and stapes). These bones stretch from the eardrum to the cochlea (your hearing organ in the inner ear). When the eardrum vibrates, it causes the ossicles to move backwards and forwards. This movement passes the sound waves through to the inner ear.
The middle ear is also connected to the space at the back of the nose by a small passage called the Eustachian tube. When you swallow, yawn or blow your nose, the Eustachian tube opens and allows air into the middle ear.
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The inner ear has two parts:
- the cochlea, responsible for hearing
- the vestibular system, responsible for balance.
The cochlea is a fluid-filled chamber that looks a bit like a snail shell. It’s lined with thousands of tiny sensory cells known as hair cells. When sound waves enter the cochlea, the hair cells trigger electrical signals in the hearing nerve. The hearing nerve sends these signals to the brain, which recognises them as different sounds – for example, people talking or footsteps.
The vestibular system is also filled with fluid and has three small chambers lined with sensory cells. When you move your head, the fluid inside these chambers moves. In response to this movement, the sensory cells create electrical signals that are sent to the brain. The brain uses this information to create a detailed idea of your body movement and head position. Together, with your vision and the sensors in your joints, this helps you keep your balance.
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