MRAudtition - Neural Bases of Speech & Language 1 THE...

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THE AUDITORY SYSTEM REVIEW OF BASIC ANATOMY I. Outer Ear - Acoustic System 1. Auricle 2. External auditory meatus 3. Tympanic membrane II. Middle Ear - Mechanical System 1. Air filled cavity. 2. Conversion of air pressure waves to mechanical vibrations occurs at the tympanic membrane. 3. Eustachian tube - small channel from nasopharynx to middle ear. 4. Auditory ossicles - ossicular chain; transmit ear drum vibrations to the fluid in the inner ear. Accomplished by leverage. III. Inner Ear - consists of a membranous labyrinth inside a body labyrinth; hydrolic system; consists of three parts: 1. Semicircular canals 2. Vestibule 3. Cochlea COCHLEA In the cochlea, mechanical vibrations for sound are converted into electrical signals that can be transmitted in the form of neural impulses to the central auditory system. There are mechanoreceptors, cochlear hair cells , which convert the mechanical movement (displacement of the hair cells) into voltage changes inside the cell (receptor potentials) which in turn cause the release of neurotransmitter and activation of the cochlear neurons of the VIII nerve. 1
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1. Small, shell shaped part of the bony labrynth contains the cochlea. 2. It resembles a tube, coiled sharply upon itself. a) apex b) base - end closest to the middle ear Cross-sections of the cochlea show the canal divided into three parts or ducts: scala vestibuli: scala tympani scala media 3. This spiral canal is fluid filled and is divided along its length by a partition called the basilar membrane . 4. Another membrane, Reissner's membrane , separates the scala vestibuli from the scala media. Within the scala media, and attached to the basilar membrane, is the receptor organ of hearing, the organ of corti. The organ of corti has numerous structures, but the ones important to us are the receptor cells themselves. These are modified epithelial cells which have hairs protruding from their surface. The hairs are in contact with an auxiliary structure, the tectorial membrane , which we'll talk more about later. The sound waves reaching the inner ear set the basilar membrane in motion, which results in a shearing force between the tectorial membrane and the hairs of the hair cells.
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This note was uploaded on 09/09/2009 for the course SPEECH AND 449 taught by Professor Rogers during the Summer '06 term at University of Washington.

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MRAudtition - Neural Bases of Speech & Language 1 THE...

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