Submitted By jiggawoot
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Approximately ten percent of the United States population is affected by some form of hearing loss (Shohet and Lee 2005). Age is directly correlated with this loss and about one-third of Americans sixty years and older have hearing problems ( There are two types of hearing loss: conductive hearing loss and sensorineural hearing loss. Conductive hearing loss results from problems in the outer and middle ear including ear wax buildup, abnormal bone growth and middle ear infections. Although this loss can be quite profound, there are many forms of rehabilitation that can aid the hearing impaired. Hearing aids to amplify sound and surgery to alleviate otosclerosis are two alternatives that significantly increase the quality of life of the elderly. However, these strategies do little good if the hearing deficiency is caused by a loss of hair cells in the inner ear (sensorineural). In this case, hearing can be restored using cochlear implants by stimulating the nerve directly (Parmet et. al 2004). Even though the implantation of the cochlear prosthesis is an expensive invasive procedure, it has been found to be quite cost effective and it increases the quality of life of the elderly. Sensorineural hearing loss can result from damage to the inner ear, specifically the inner hair cells of the cochlea ( In order for sound waves to be transduced into nerve impulses, they must first travel through the outer ear, vibrating the tympanic membrane. The vibrations of the tympanic membrane are transferred through the middle ear to the oval window, where they cause the fluid of the cochlea to move ( This movement causes the inner hair cells to move, leading to transduction. Since hair cells do not regenerate, damage to them can greatly reduce transduction resulting in hearing loss. Cochlear implants can restore some hearing by bypassing the damaged hair cells and creating action potentials in the auditory nerve. The process by which the auditory nerve is stimulated is simple, yet elegant. First, the microphone, which is fitted around the ear, receives sound signals from the environment. The signals are changed into digital information via the sound processor and transmitted to the implant, which is inserted surgically (Parmet et. al 2004). To reduce the risk of infection, the sound processor and implant are connected and held in place with magnets, instead of being connected with wires. ( The implant converts the digital signals into electrical impulses, which are sent through wires to the corresponding electrodes implanted within the cochlea (Parmet et. al 2004). These electrodes stimulate the auditory nerve at different locations depending on their tonotopic location within the cochlea (Rauschecker and Shannon 2002). Based on their placement, the electrodes have access to all but the lowest of the frequency range. Since the higher brain pathway can “add” these missing frequencies, accessing this location of the cochlea is unnecessary (Rauschecker and Shannon 2002). Although cochlear implants can give the deaf “a useful auditory understanding of the environment and help him or her to understand speech,” they do not restore hearing to normal ( So far more than 40,000 people received cochlear implants. (Rauschecker and Shannon 2002). Even though cochlear implants successfully allow people to regain some level of hearing, it does not help everyone equally. Patients who have sensorineural hearing loss or became deaf after learning speech usually get the most out of the cochlear implants in the shortest amount of time. They can usually “reconnect almost immediately after receiving the [cochlear implant]” (Rauschecker and Shannon 2002). Individuals who are postlingually deafened are