Structure of the ear
The middle ear is an air-filled compartment. Inside it are the three smallest bones in the body, called malleus, incus and stapes. These bones are connected to each other. The last in the group, stapes, also makes contact with the internal (inner) 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 semicircular 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 you hear?
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 range of sounds.
How do you keep your balance?
The brain uses the visual system to help orientate us in our surroundings. The vestibular system detects both circular motion and movement in a straight line. This includes everyday actions such as stopping, starting or turning. The sensory system keeps track of the movement and tension of our muscles and joints. It also monitors the position of our body with respect to the ground. The brain receives signals from all these systems and processes the information gathered to produce a sensation of stability.
The tubes and sacs within the vestibular system are filled with fluid. When we move our heads, this fluid also moves. The vestibular system also contains specialised sensory cells. Movement of the fluid causes these sensory cells to bend. This change results in an electrical signal which is carried, via a nerve, to the brain for interpretation.
Once the brain has interpreted the signals as movement, it controls your eyes so that they keep providing information about your position. The brain also sends signals to your muscles so that they help to ensure balance regardless of the position of your body.
Some common disorders of the ear
Barotrauma of the ear
Benign paroxysmal position vertigo
Eustachian tube dysfunction
Labyrinthitis and vestibular neuritis