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11.AUD-InnerEar

Audiology SLP314

TermDefinition
Inner ear (2 parts) -Vestibular system (vestibule, semicircular canals) -Auditory system (cochlea) Laberynthitis can result in hearing AND balance problems.
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) -
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
Membranous labyrinth (3) 1.Reissner's membrane, 2.tectorial membrane, 3.basilar membrane
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
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.
Function of Cochlea Mechanical energy of sound changed to neural info in inner ear. (Mechanical to Neural transduction)
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.
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
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.
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).
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.
Functions of auditory portion of the inner ear (2) 1.frequency analysis 2.mechanoelectrical transduction (vibration is amplified and converted into electrical energy)
Created by: ashea01
 

 



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