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| Sunday, 23 April 2006 |
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Junior Observer |  |
| News Business Features Editorial
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Body talk A marvel of intricacy and design No matter what you do, your ears are always working. They are constantly detecting, decoding and analysing sounds and communicating them to the brain. In a comparatively tiny area of our body the ear is performing many highly technical and intricate functions. What we see of the ear is just the outer part of a very complex structure. There are three distinct portions to the ear: the outer ear containing the fleshy skin and the canal that leads to the inner ear, the middle ear, containing the three smallest bones in the human body - the malleus, incus and stapes (commonly called the hammer, anvil and stirrup) and the inner ear, made up of a cluster of three semi-circular canals, and the snail shaped cochlea. The outer ear The outer ear collects sound waves in the air and channels them to the inner parts of the ear. The outer ear along with its canal has been shown to enhance sounds within a certain frequency range. That range just happens to be the same range that most of the characteristics of human speech sounds fall into. This allows the sounds to be boosted to twice their original intensity. The middle ear The middle ear transforms the acoustical vibration of the sound wave into mechanical vibration and passes it onto the inner ear. The three tiny bones of the middle ear act as a lever to bridge the eardrum with the oval window. Incoming forces are magnified by about 30 per cent. This increased force allows the fluid in the cochlea of the inner ear to be activated. The inner ear The semi-circular canals in the inner ear allow us to maintain balance and coordination. The cochlea, which is a bundle of three fluid filled canals coiled up in a spiral, is set in motion by the stirrup in the middle ear. Moving in and out, it sets up hydraulic pressure in the fluid.
As these waves travel to and from the apex of the spirals, they cause the walls separating the canals to undulate. (have a wavy motion) Along one of these walls is a sensitive organ called the corti. It is made up of many thousands of sensory hair cells. From here, thousands of nerve fibres carry information about the frequency, intensity and timbre(the quality of the sound in a voice) of all these sounds to the brain, where the sensation of hearing occurs. Scientists cannot fully explain just how the signals are transmitted to the brain. They do know that the signals sent by all the hair cells are about the same in duration and strength. This has led them to believe that it is not the content of the signals, but rather the signals themselves that convey some sort of message to the brain. Our ears, so often taken for granted, thus are a marvel of intricacy and design that leaves anything that man can produce in the shade as a cheap imitation. Your hearing can never be replaced. Don't take it for granted. Compiled by Chamitha **** Fact file * The human ear can cope with an incredible range of sound. Your ear can, in fact, cope with a 10,000,000,000,000 fold difference in loudness. That's a range of 130 decibels. * The ear can pick out and focus on a particular sound or conversation in a roomful of noise. * The human ear can detect a difference of just two degrees in the direction of a sound source. * The ear is able to recognise at least 400,000 different sounds, matching them up against those stored in the memory banks. * The ears contain structures for both, the sense of hearing and the sense of balance. The eighth cranial nerve (vestibulocochlear nerve made up of the auditory and vestibular nerves) carries nerve impulses for both hearing and balance, from the ear to the brain. * Sound waves cause the tympanic membrane (eardrum) to vibrate. Humans can hear sound waves with frequencies between 20 and 20,000 Hz. The three bones in the ear (malleus, incus, stapes) pass these vibrations on to the cochlea. The cochlea is a snail-shaped, fluid-filled structure in the inner ear. **** Hearing Loss People can lose all or part of their ability to hear because of loud noises, infections, head injuries, brain damage and genetic diseases. Hearing loss is common in older people. There are several types of hearing loss: * Conductive hearing loss occurs when sound vibrations from the tympanic membrane to the inner ear are blocked. This may be caused by ear wax in the auditory canal, fluid buildup in the middle ear, ear infections or abnormal bone growth. * Sensorineural hearing loss occurs when there is damage to the vestibulocochlear (auditory) nerve. This type of hearing loss may be caused by head injury, birth defects, high blood pressure or stroke. * Presbycusis: occurs because of changes in the inner ear. This is a very common type of hearing loss that happens gradually in old age. * Tinnitus: people with tinnitus hear a constant ringing or roaring sound. The cause of this ringing cannot always be found. Some cases of tinnitus are caused by ear wax, ear infections or a reaction to antibiotics, but there are many other possible causes of this disorder.
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