The Auditory System.pptx - THE AUDITORY SYSTEM REVIEW OF...

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THE AUDITORY SYSTEM
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REVIEW OF ANATOMY AND PHYSIOLOGY
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FUNCTIONS OF THE EAR STRUCTURES The pinna collects sounds waves and channels them into the auditory meatus. The hairs and cerumen in the canal help prevent foreign objects from reaching the tympanic membrane. The tympanic membrane vibrates when sound waves hit it; the sound vibrations are conducted to the malleus. The bones of the middle ear transmit the sound vibrations to the inner ear: malleus to incus to stapes, where sound vibrations are transmitted to the oval window. The motion is transferred to the fluid in the inner ear.
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FUNCTIONS OF THE EAR STRUCTURES Fluid motion in the inner ear stimulates the sound receptors in the cochlea and the organ of Corti, where impulses are transmitted to the cochlear branch of the vestibulocochlear nerve (CN VIII). * Eustachian tube helps equalize pressure in the middle ear. * Receptors responsible for equilibrium (balance) are located in the inner ear, within the bony vestibule and at the base of the semicircular canals. Impulses from the equilibrium receptors are transmitted to the brain via the vestibular branch. Cerebellum is important in mediating the sense of equilibrium and balance.
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AGING Cerumen becomes harder, containing less moisture, and its buildup within the ear may contribute to a hearing loss in the low-frequency range. The tympanic membrane loses elasticity. The joints between the auditory bones become stiffer; the stiffness interferes with the transmission of sound waves, but is not clinically significant by itself. There is a gradual loss of the receptor cells in the organ of Corti after age 40. With increasing age, the number of nerve fibers in the vestibulocochlear nerve decreases, contributing to hearing loss and sometimes affecting balance and equilibrium.
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HEARING LOSS 2 types: Conductive: caused by a problem transmitting sound impulse through the auditory canal, the tympanic membrane, or the bones of the middle ear. Most often occurs from stiffening of the bones of the middle ear or from scarring of the tympanic membrane Sensorineural: disorder of a hearing nerve Accounts 80% of hearing loss incidences. Can be produced from continued exposure to excessively high levels of sound. Risk: people working in machinery operation that creates loud noises. (The standards of the Occupational Safety and Health Administration [OSHA] require the wearing of ear protectors in such settings.) Can also be caused by arteriosclerosis due to a decreased blood flow to the otic nerve.
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CAUSES OF HEARING LOSS Conductive Obstruction by impacted cerumen
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