EAR ANATOMY AND PHYSIOLOGY
Structure and function of the ear
- auricle - the outer part of the ear, situated on either side of the head.
- ear canal - lined with skin, it passes from the hole in the auricle through cartilage and bone to the tympanic membrane (ear drum).
- tympanic membrane - the thin transparent piece of skin at the end of the ear canal.
- outer ear - the auricle, ear canal and outer surface of tympanic membrane.
- middle ear - a small air-filled bony chamber that contains three small bones connecting the tympanic membrane to the inner ear.
- inner ear - This consists of two parts:
- cochlea - a small shell-shaped, fluid-filled structure with many small hairs along its length
- semi circular canals - structures filled with fluid.
- vestibulo-cochlear nerve - connected to both the cochlea and semi circular canals, it connects the inner ear to the brain.
Function of the ear
When a trumpet produces a sound, it sets up vibrations (in the air) that are trapped by the auricle, and conducted to the tympanic membrane, that then vibrates. This causes movement of the three small bones in the middle ear that, in turn, transmit the vibrations to cause ripples in the cochlear fluid. These stimulate the hairs to move, thereby affecting the vestibulo-cochlear nerve that sends messages to the brain that recognises the sound as a trumpet blowing. Higher pitched sounds cause more hairs to vibrate than do the lower sounds.
The semi circular canals respond to changes in body position and send messages to the brain, thereby helping to control balance.
For unknown reasons, people with Usher syndrome become deaf because damage occurs to the hair cells that vibrate in the cochlear fluid. This damage may increase with age. Thus, when a sound is made near the auricle, it will pass through the canal to the middle ear. However, subsequent transmission of the sound to the cochlea will be faulty and hence the sound will be inadequately passed along the vestibulo-cochlear nerve or recognised by the brain.
Syndromes that affect vision and other bodily functions
- people are born deaf or with partial hearing loss, and develop RP in late childhood or early teen years.
- degeneration of both the retina and choroid
- RP with possible physical abnormality, obesity, kidney disease and mental retardation.
- RP with progressive neurological problems.