The Ear
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Vibrations enter the outer ear via the pinna (auricle), the portion of the ear visible from the outside, which collects the vibrations and funnels them into the ear canal (external auditory meatus) (How). The ear canal is about an inch long and a quarter inch in diameter, and extends from the pinna to the eardrum. The vibrations then reach the eardrum (tympanic membrane) at the end of the ear canal and the beginning of the middle ear. The middle ear contains the ossicles, three tiny bones which move back and forth with the vibrations, changing the sound waves into mechanical vibrations. The first bone is called the malleus (hammer), and is connected to the eardrum (How). The malleus is connected to the second ossicle, the incus (anvil), which in turn is connected to the third ossicle, the stapes (stirrup). The mechanical vibration is transmitted through the three bones, and causes an in-and-out movement of the base of the stapes, the stapes footplate, in patterns that match those of the incoming sound waves. The stapes footplate fits into the oval window, which is the beginning of the inner ear. The vibrations then reach the inner ear which contains the sensory organ for hearing (How). The part of the inner ear related to hearing is called the cochlea. It is a bony structure shaped like a snail and filled with fluid called endolymph and perilymph. The sensory receptor in the cochlea is the organ of Corti, which holds the hair cells which are the nerve receptor
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he two ears might imply damage to one ear. It could also be due to a build up of wax in one ear more than the other. Infection in one ear may also cause a loss of auditory acuity in the infected ear. Auditory acuity is lost with age, and it may not be lost equally bilaterally, which would explain a difference between the acuity in the two ears in older people.
Sound waves reach the cochlea when conduction deafness is present through vibrations of the bones in the skull, bypassing the outer and middle ear (Bone). Hearing is not as efficient through bone conduction as it is through air conduction, but it is possible. Hearing aids are available for people with conduction deafness which consists of a body-worn aid and a bone conductor or vibrator attached to a headband, or it can be attached to special spectacles. Bone hearing aids can also be implanted.
Nystagmus is an involuntary, constant, cyclical movement of the eyeball, which can be in any direction (Thomas, û46). It can be caused by disorders of the labyrinthine vestibular system of the ear.
Vertigo is the sense of moving around in space, or of objects moving around a person (Thomas V-19). The subject with vertigo has difficulty maintaining equilibrium and bala
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Approximate Word count = 1508
Approximate Pages = 6 (250 words per page)
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