”I am Your Body”

EAR

    
YOU ARE IMPRESSED by the computer your company bought not long ago. It will perform seeming miracles, but to me it is as crude as a concrete mixer. Perhaps I am prejudiced, for I am a triumph of miniaturization. Nowhere in your body is so much crammed into so small a space as in me. I have enough electrical circuits to provide phone service for a good-sized city. I am also a kind of automatic pilot, keeping you from toppling over.
I am your right ear, and I do all this in a space not much larger than a hazelnut! You consider your eyes your most important sensory organs. Yet, without my partner and me, you would be doomed to solitary sonic confinement-far more emotionally-disabling than blindness.

You think of me simply as that flap of tissue on the side of your head. This outer ear, however, is nothing but a sound-gathering trumpet. From it, a one-inch canal runs obliquely to the eardrum, twisting to protect my delicate inner components and warming air to keep things cozy. In this canal, a profusion of hairs and 4000 wax glands act as a flypaper trap for insects, dust and other potential irritants. Further, the wax guards against infection, particularly when you swim in dirty water. (You can wash away unsightly wax but I wish you wouldn't pick at the rest you could harm my eardrum, and I'll shed excess wax naturally).

My eardrum a tough tightly stretched membrane less than half an inch across, is where the intricate business of hearing starts. Sound-bearing airwaves strike it-like a stick beating a drum. Even faint vibrations from a whisper can push it inward but ever so little, perhaps only a billionth of a centimeter. This minute displacement is then changed, in an awe-inspiring chain of events not yet entirely understood, into meaningful sound for you.

To see how, step through my drumhead to your bean-size middle ear. Here are hinged together three tiny bones called the anvil, hammer and stirrup (also known as the stapes) because they vaguely resemble those things. It is their job to step up the tiny movements of my drum, amplifying them 22 times and passing them on to my inner ear via an oval window attached to the stirrup.

My inner ear-the real organ of hearing-resides in a fortress like cavern hollowed out of the body's hardest bone and filled with watery fluid. Its major hearing component is the snail-shaped cochlea, whose twisting interior is studded with thousands of microscopic hair like nerve cells, each one tuned to a particular vibration. When the middle ear's stirrup "knocks" on the oval window leading to the inner ear, this fluid is set vibrating. If middle C has been sounded, say, then the cochlea's middle C's hair cell vibrates, waving in the lymph fluid like seaweed a tidal current.

The waving produces a wisp of electricity that feeds into my auditory nerve (only the diameter of a pencil lead, this nerve contains more than 30,000 circuits!), which in turn lead to your brain three fourths of an inch away. My cochlea may feed in thousands of electrical messages, with your left ear doing the same. It's the brain's job to unscramble these data and convert them into meaningful sound. Thus, you hear with me, but in your brain.

So far I've talked only of sound conducted by airwaves. You can also hear by bone conduction. When you speak, part of the sound leaves your mouth and strikes my drum, but another part travels directly to my inner-ear fluid via the jawbones. Thus, what you hear is quite different from what a listener hears. That's why you have trouble recognizing your own voice on a tape recorder. It's also why you think you are making quite a racket when you eat celery.

But hearing is only part of the story of my miraculous inner ear. Above, the cochlea I have three minute, fluid-filled, semicircular canals. These loops of tubing are your organs of balance. One detects up-and-down motion, another forward motion, the third lateral motion. If you start to fall, fluid in one of my canals is displaced. Hair cells there detect this, and inform your brain, which orders muscles to tighten to keep you upright.

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