Sample Essay on the Mechanism of Hearing

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The hearing machinary of our body consists of three parts: the outer, middle and the inner ear. The outer ear comprises of two curled shells each on either side of the head and a tissue thin membrane, about the diameter of a pencil, tightly stretched like drum-head, which lies in-between the outer and the middle ear.

The middle ear consists of a hollow cavity barely large enough to hold five or six drops of water. A set of three tiny bones, the hammer (malleus), anvil (incus) and stirrups (stapes) span across the empty space. At one end of the chain the handle of hammer is connected to eardrums while towards the inner side stirrups are fastened to another membrane, an oval window about the size of a pin-head. This membrane separates the middle ear cavity from the fluids and the canals which form the inner ear and control our sense of balance. Immersed in the fluid are numerous hair cells or ciliary cells lining the inner-ear chamber?

In the process of hearing sound waves are funnelled in ear canals, strike the ear drums and make it vibrate. These vibrations travel along the boon chain (hammer, anvil and stirrups) to the oval window which transmits them to the fluid in the inner ear.

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Through nerve endings in the inner ear whose magic is still little understood, these vibrations are translated into electrical impulses which are flashed along nearly 30,000 fibres of auditory nerve to the brain and we hear a sound. The hair cells or ciliary cells which line the inner ear canals and chambers play an important part in picking up these vibrations. Obviously with such a delicate mechanism many things can go wrong, if we subject it to too much strain.

The Measurement of Sound:

The intensity or loudness of sound is measured on a scale called decibel scale or dB-scale. It measures the loudness of sound in terms of relative units of energy or power on a logarithmic scale in accordance with the response of human ear. The scale starts from O dB which is considered as the threshold of hearing – the faintest sound which human ear can hear.

A sound of 10 dB is 10 times louder than O dB. A sound of 20 dB is 10 x 10 or 100 times louder, of 30 dB 10 x 10 x 10 or 1000 times, 40 dB is 10 x 10 x 10 x 10 or 10,000 times while a sound of 50 dB is 10 x 10 x 10 x 10 x 10 or 100,000 times louder than the threshold of human hearing.

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