How We Hear
The ear is our most complex sensory organ, vitally important for communication. The ear is made up of 3 parts:
> Outer Ear - pinna, ear canal & ear drum
> Middle Ear - malleus, incus & stapes
> Inner Ear - cochlea & auditory nerve
Each of these three parts has a special function that allow us to hear.
1. Sound waves are collected by the outer ear (pinna) and channelled along the ear canal to the eardrum.
2. When the sound waves reach the eardrum, the impact creates vibrations which are transferred through a series of three tiny bones (malleus, incus & stapes) in the middle ear.
3. The stapes is connected to the cochlea, a delicate, snail shaped structure in the inner ear. The cochlea is filled with fluid and thousands of microscopic hairs.
4. The vibrations are transmitted to the fluid in the cochlea, which in turn bends the hair cells. The bending of these hairs sets off nerve impulses that are then passed through the auditory nerve.
5. The auditory nerve carries the signal to the brain, which translates the impulses into what we perceive as 'sounds'.
Hearing Loss
There are three types of hearing loss:
> conductive
> sensorineural
> mixed
While a symptoms for each loss may be similar, the cause can be very different.
A conductive hearing loss is caused by a problem with the outer or middle ear. Some outer ear problems are a result of impacted cerumen (wax), external otitis (infection of the skin of the ear canal) and congenital deformities. Middle ear problems can be caused by ear infections or fluid behind the eardrum (otitis media), immobility or disconnected middle ear bones. A conductive hearing loss is not always permanent and can often be treated medically or surgically.
A sensorineural hearing loss is permanent and is a result of damage to the cochlea or auditory nerve. Some causes are presbycusis (hearing loss associated with ageing), noise exposure, acoustic neuromas, drugs, mumps, measles and Meniere's disease. A sensorineural hearing loss cannot usually be medically or surgically treated – hearing aids or cochlear implants are the best solution.
A mixed hearing loss is a combination of a conductive and sensorineural hearing loss.
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