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THE LISTENING EAR

By: Tuvia Cohen



The ear is a remarkable machine, containing advanced capabilities. It receives waves of sound from the atmosphere which then travel invisibly through both air, and solid objects (this is why you can you hear the sound of traffic through a closed window). Having received these signals, our little internal machine then sends them to the brain, where they are converted back into meaningful sound. Let us take a closer look at this extraordinary little wonder-box, strategically positioned on either side of our heads.

Of all the body parts, the ear has perhaps the most weird and wonderful shape. Its whirls and curls are asymmetrical, and seem to demand an explanation. Theirfunction is to gather sound waves as they travel through the air, and it is because of their shape that they perform so superbly. The story is told of an architect who once designed a prison in the shape of a human ear. By positioning himself in the very center of this most unusual structure, the chief warden was able to hear every sound and conversation spoken in the entire prison. As unlikely as it seemed at first, the scheme worked!

Once the sound wave – which is akin to air on the move – is picked up by the ear, it enters a twisting and winding channel before reaching the eardrum. The twists and turns, like all components of a complicated structure, are not haphazard. There are hairs that line the tunnel, which function like an impressive avenue of wax factories along the route. In a designed machine, everything has a purpose. If the ear canal was quite straight, any young child could too easily and inquisitively poke a potentially damaging instrument through. These twists and turns protect the ear’s delicate inner components, and give the air that enters it a chance to warm up before meeting the eardrum. What consideration!

The profusion of hairs and wax glands (four thousand!) act like a fly-paper trap for insects, dust, and other irritants. The wax guards against infection, particularly when swimming in dirty water. Imagine a long road, and on either side of it, stretching as far as the eye could see, factory after factory producing wax candles. What a hive of activity would ensue! What a vast quantity of raw materials, oils, fats, electricity and transport would be required! Above all, what a huge industrial project it would be! Yet, we are not to worry –
for we have four thousand individual factories deposited in a one-inch canal on either side of our heads, faithfully producing wax, day after day. Most of us would not have the slightest idea how to produce a wax candle – yet our ears do possess that knowledge.

The question is, how were they taught?

Introducing the eardrum – a tough, tightly-stretchedpiece of skin, about half an inch across. No water can penetrate it, which explains why we don’t fill up with water while swimming! When sound-bearing air waves strike the eardrum, they set it vibrating. The sensitivity of the eardrum is such that even a whisper from across the room can cause this to happen. But don’t expect to see it shake. As it vibrates, the ear moves just one billionth of a centimeter. It’s the minutest of movements but it produces a chain reaction to give us recognizable sounds.

Behind the eardrum, in the area called the middle ear, live three tiny bones – the smallest bones in the body. Commonly known as the anvil, hammer, and stirrup because of their distinctive shapes, these bones are delicately hinged together. In response to the tiny vibration of the eardrum, they vibrate in turn – only thirty times stronger. The amplified vibrations are then passed on to the inner ear via the oval window attached to the stirrup. The positioning of these three tiny bones is crucial. Any slight deviation to protocol would render the whole system ineffective.

Now for the most amazing section of our tour – the inner ear. This section is a fortress-like cavern, hollowed out of the hardest bone on the body, and filled with a watery fluid. Its major component is a snail-shaped coil called the cochlea, whose twisting interior is studded with thousands of microscopic hair-like nerve cells.
In response to the vibrations passed through the oval window, the cochlea’s tiny hairs wave in the fluid, like seaweed in a tidal current. Incredibly, this waving generates a minute wisp of electricity that feeds into the auditory nerve and leads into the brain just three quarters of an inch away.

In all, thousands of different messages pour simultaneously into the brain, which adeptly unscrambles the flood of data and communicates clearly the everyday sounds we hear. For example, the alarm clock is ringing – time to get up!

As if this weren’t impressive enough, every sound received by the brain is carefully stored away in the memory bank for future reference. Once heard, a voice, a message or a distinctive sound, is recognized by the ear for all time. Can you conjure up in your mind the sound of rain on a tin roof? Rustling leaves? The blast of the Shofar? Well then, there you have it!

How is it possible for the eardrum, consisting only of tiny bones and drifting fluid, to transmit not only one sound, but many different sounds, all at the same time? Think about it: At any one instant, you can hear someone talking to you, theticking of a clock, a door closing and the telephone ringing. All the sounds are different, yet all are transmitted. Even the vibrations of the eardrum, a seemingly simple mechanism, are actually enormously complex. Add to that the many sophisticated refinements that the system possesses – one, to block out unwanted background sounds, another to reduce the level of damaging volume as things heard crash through the ear, yet another to repair the ear drum should it become perforated – and it’s clear that theear – though not much larger than a hazelnut – is a masterpiece of foresight and design.

Tuvia Cohen is a humorist, scientist, and an accomplished author.