Our modern world is an extremely noisy world. We live in a cacophony of man-made sound that our ancestors could never have imagined.

Their world was a quiet world. If we had lived during the first half of the 18th century, the loudest sounds might have been the clip-clopping of horses’ hooves and the rumble of cart-wheels. But the means by which our ancestors’ ears received sound was exactly the same as it does for ours today.

The parts of the human ear

The human ear has been described as “a miracle of precision engineering”. (see diagram) There are three separate parts, the outer ear canal (which is the only part you can see), the middle ear, and the inner ear. Dividing up these three parts are two membranes, the outer, bigger one being the eardrum, and the inner, smaller one being the “oval window”.

How does the ear work?

Whatever makes the sound causes sound waves to expand in the air like ripples on water. These sound waves come floating into the outer ear canal, each one in turn pushing the eardrum inwards. The faster the sound waves hit the eardrum, the higher the pitch of the sound. So, the eardrum vibrates to and fro in time to the sound waves. Inside the middle ear is where the amazing mechanical action takes place. Three tiny bones, whose popular names are the “hammer”, the “anvil”, and the “stirrup”, are linked together. 

The hammer is attached to the inside surface of the eardrum. As the eardrum vibrates, it shakes the hammer, which shakes the anvil, which shakes the stirrup. These three bones have the effect of gearing down the movements of the eardrum. The stirrup’s movements are therefore less expansive, more precise, and stronger than the original movements of the eardrum. The stirrup is attached to the “oval window”, a much smaller version of the eardrum. (There is another membrane between the middle ear and the inner ear. It is called the “round window”.Its purpose is simply to balance the movements of the “oval window”. Each time the oval window vibrates, so the round window vibrates in the opposite direction.) 

As the stirrup and the oval window vibrate, fluid that is contained in the inner ear vibrates in sympathy. Here is where a further miracle takes place: inside the fluid are tiny hair cells. The shaking of the fluid stimulates the hair cells, allowing them to send electrical nerve impulses to the brain which the brain translates as the sounds that we interpret as voice, speech, music, or loud sounds such as explosions. The only other parts of the inner ear are the “semi-circular canals” which have nothing to do with hearing, but simply allow you to balance, and the “eustachian tube” which connects with the throat and the outer atmosphere. This tube is what pops when you change altitude.

The ear is very delicate

From the above explanation it can be seen that the mechanism of the ear is extremely delicate and vulnerable to very loud sounds. But Nature has provided some safeguard against sounds which might damage the ear. Whenever the eardrum senses a very loud sound, it instinctively tenses itself, in much the same way as the eyelid blinks to protect the eye against a sudden bright flash of light. The trouble is that if sounds are received by the ear that are too loud for it to transmit, or last too long, or repeat themselves over and over, then the ear gives up trying to protect itself, and can get damaged, either temporarily or permanently. Another thing which many people do not realise is the older you are, the less able your ear is to protect you against loud sounds. These can now cause pain.

* Coyne studied anatomy and physiology of the ear at University of Manchester. Founding Principal of Fulton School for the Deaf, Gillitts. KZN