Structure of the Ear

The ear is divided into three parts. The outer (external) ear includes the part you can see, called the pinna, and the narrow tube-like structure - the ear canal. At the end of the canal is the eardrum. This separates the external ear from the middle ear. The eardrum is a tightly stretched membrane, a bit like the skin of a drum.
The middle ear is an air-filled compartment. Inside it are the three smallest bones in the body, called the malleus, incus and stapes. These bones are connected to each other. The last in the group, stapes, also makes contact with the inner (internal) ear. The air space of the middle ear connects to the back of the nose by the Eustachian tube.
The inner ear is made up of two components. The cochlea is involved with hearing. The vestibular system helps with balance. The cochlea is a snail-shaped chamber filled with fluid. It is lined with special sensory cells called hair cells.
These cells transform sound waves into electrical signals. The cochlea is attached to a nerve that leads to the brain. The vestibular system is made up of a network of tubes, called the semi-circular canals, plus the vestibule. The vestibular system also contains special sensory cells, but here they detect movement instead of sound. Both the cochlea and the vestibular system are connected to a nerve which carries electrical signals to the brain.

How Do We Hear?

Sound waves are created when air vibrates. To hear, the ear must change sound into electrical signals which the brain can interpret. The outer part of the ear (the pinna) funnels sound waves into the ear canal. When sound waves reach the eardrum they cause it to vibrate. Vibrations of the eardrum cause the tiny bones in the middle ear to move too. The last of these bones, stapes, and passes on the vibrations to the fluid-filled chamber called the cochlea. When the cochlea receives the vibrations, the fluid inside it moves. As the fluid moves it causes the special sensory cells to create an electrical signal. This electrical signal is sent to the brain. Special areas in the brain receive these signals and translate them into what we know as sound.
Your ears create electrical signals that represent an extraordinary variety of sounds. For example, the speed at which the eardrum vibrates varies with different types of sound. With low-pitched sounds the eardrum vibrates slowly. With high-pitched sounds it vibrates faster. This means that the special hair cells in the cochlea also vibrate at varying speeds. This causes different signals to be sent to the brain. This is one of the ways we are able to distinguish between a wide ranges of sounds.

What can cause hearing loss?

Damage to any part of the ear can cause a hearing loss. If there is a problem in the ear canal or the middle ear, this causes what is known as a conductive hearing loss. In conductive hearing loss, the movement of sound (conduction) is blocked or does not pass into the inner ear. There are several causes of conductive hearing losses and this may result in a permanent or temporary hearing loss. A common cause in children is the build-up of fluid in the middle ear space, otherwise known as glue ear. For more information see separate leaflet called Glue Ear.
If the fluid-filled chamber called the cochlea or the hearing nerve is not working properly this causes what is known as a sensor neural hearing loss. Usually this means that hair cells in the cochlea are not working properly or there is a problem with the hearing nerve so that some or all sounds are not being sent to the brain. Sensor neural hearing losses are usually permanent. They can be mild, moderate, severe or profound and affect one or both ears.
It is also possible for sensor neural and conductive hearing losses to occur together in a mixed hearing loss.