Audiology SLP314
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| Inner ear (2 parts) | -Vestibular system (vestibule, semicircular canals) -Auditory system (cochlea)
Laberynthitis can result in hearing AND balance problems.
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| COCHLEA | 2 3/4 coils -Base (oval and round window) -Apex (helicotrema at top of spiral) -Modiolus (finely perforated bone at core contains nerve fibers and blood supply) -
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| 3 fluid-filled compartments | 1. Scala vestibuli-upper chamber(perilymph)(connects to vestibule/OW) 2. Scala tympani-lower chamber (perilymph) (connects to RW) 3. Scala media- middle chamber (endolymph) (contains Organ of Coati) -Helicotrema connects SV/ST
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| Membranous labyrinth (3) | 1.Reissner's membrane, 2.tectorial membrane, 3.basilar membrane
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| Organ of Corti (5) | 1.Pillar cells, form tunnel of Corti 2.Inner hair cells -3000 in single row 3.Outer hair cells-12,000-15,000 in 3 rows 4.Stereocilia: tiny hairs at top of hair cell. 5.Afferent auditory nerve fibers: connect to HCs at their base
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| Afferent nerver fibers | 8 fibers/IHC (90-95%). 10 OHCs/fiber (5-10%). All fibers exit Organ of Corti thru modiolus in bunches of ~30 to form cochlear branch of CN VIII.
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| Function of Cochlea | Mechanical energy of sound changed to neural info in inner ear. (Mechanical to Neural transduction)
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| Traveling Wave (TW) | Vibratory motion of the BM. Peak (ie. point of maximal displacement) varies as a function of frequency. Reaches max, then decays rapidly.
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| Tonotopic organization | Orderly arrangement of freqs along basilar membrane. High freqs at base, low freqs at apex. 1.Mass - BM progressively widens from base to apex 2.Stiffness gradient- 300x more stiff at base than apex
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| Stria vascularis | Maintains positive potassium charge (+80mV). Bending of stereocilia causes potassium ions to enter HCs *creates a chemical current - flow of electrically charged ions from endolymph into hair cell.
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| Function of OHCs | -Amplifies vibration of BM during TW. -Enhances shearing force to IHCs by factor of 1000. -Lose OHCs and IHCs lose sensitivity. -Prestin causes the movement (similar to protein in muscle fibers, which also expand and contract).
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| Role of IHCs | Shearing force, cilia bend, K+ flows into cells. IHCs send neurotransmitter across synapse to dendrites of AN fibers. Neurotransmitter causes neurons to fire. Neural discharges are carried along auditory nerve up to brainstem.
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| Functions of auditory portion of the inner ear (2) | 1.frequency analysis 2.mechanoelectrical transduction (vibration is amplified and converted into electrical energy)
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