I began to think about ears and hearing during a recent Children’s Day. In one of the large shopping centers they had dedicated the stage area for children’s entertainment. The noise from the battery of boom boxes was so loud that foreigners were walking through the shopping mall with their fingers in their ears. Without the benefit of a sound pressure level machine to get an accurate reading, I would estimate that the children were being exposed to around 120-125 decibels (dB). The significance of this, is that adult workers should not be exposed to more than 90 dB for an eight hour day (legislated in many countries). Children should be exposed to much less.
I have always wondered why musical performances/entertainment in this country need the volume control wound right up. Now I know. The audience has been rendered deaf after a few Children’s Day experiences! This also goes a long way towards explaining why the local populace does not hear phones ringing, and why the girl in the next office has her mobile phone ring tone set on maximum. I know she has an incoming call before she does!
However, the reason for deafness is not all the result of Children’s Day. There are other reasons, including (dare I say it) getting older! The effects of aging start around 20 years of age, and our hearing starts a gradual decline. Higher frequencies are usually the first to go. This age-related hearing loss is normal and is similar to the age-related effects with vision.
The two main types of deafness are called Conductive deafness and Nerve deafness. Deafness at birth is known as congenital deafness, while deafness that occurs after birth is called adventitious deafness, and the most common cause of adventitious deafness is noise, which accounts for over one quarter of people affected by hearing loss (which gets us back to Children’s Day).
A brief look at the anatomy of the ear will help understanding the causes of deafness. The ear is made up of three different parts, including the outer ear which is the part you can see. Its shape helps to collect sound waves. A tube, called the external ear canal, leads inward to the eardrum.
The middle ear is separated from the outer ear by the eardrum. The middle ear contains three tiny bones called the malleus (hammer bone), the incus (anvil bone) and the stapes (stirrup bone). These bones amplify the movement of the eardrum produced by sound waves making the drum move in and out. The Eustachian tube connects the middle ear to the back of the throat and helps to equalize air pressure.
The inner ear is where the sound waves are picked up by a tiny spiral-shaped organ called the cochlear. Hairs on the cochlear sense the vibrations and pass the message as electrical impulses to the brain via the cochlear nerve.
Now, Conductive deafness is caused by the failure of the three tiny bones inside the middle ear to pass along sound waves to the inner ear. Another common cause of conductive deafness is the failure of the eardrum to vibrate in response to sound waves. A build-up of fluid in the ear canal, for example, can dampen the movement of the eardrum. In many cases, treatment is available for conductive deafness and normal hearing will return.
Nerve deafness is caused by disease, trauma or some other disruptive event targeting the cochlear nerve. The rest of the ear, including the tiny bones and eardrum may be working, but the electrical impulses cannot reach the brain. Most cases of nerve deafness do not respond to treatment.
Remember that Deafness can range from mild to profound and has multifactorial causes including injury, disease and genetic defects, and excess noise accounts for over one quarter of people affected by hearing loss.