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NS44 Hearing + Vestibular Function (ii) (Rinne test (evaluates air + bone…
NS44 Hearing + Vestibular Function (ii)
Organ of Corti
responsible for sound transduction
located in the scala media (a.k.a cochlear duct) between the scala vestibule and scala tympani
composed of mechanosensory hair cells.
tuned into different frequencies
high frequencies @ base
low frequencies @ apex
Basilar membrane
between scala media + scala tympani
frequency analyser
distributes sound along organ of corticosteroids so hair cells can respond to their specific frequency
movement of membrane causes bending of cilia on outer part of hair cells
causes change in cation conductance in apical ends of hair cells
change in membrane potential
deafness
conductive
impaired sound transmission in outer/middle ear
due to wax, foreign body, infection, perforated tympanic membrane
sensorineural
destruction of hair cells (usually in certain part)
due to loudness, vasc lesions, drug ototoxicity (aminoglycosides, loop diuretics, NSAIDs, PDE5 inhibitors, platinum agents)
diagnosed by audiometry
Weber test
evaluates lateralisation
place vibrating tuning fork on top of patient's head
normal: heard equally on both sides
conductive deafness: louder in affected ear
sensorineural deafness: quieter in affected ear
Rinne test
evaluates air + bone conduction
place vibrating tuning fork on mastoid process until patient can no longer hear sound, then move it near EAM + ask if they can hear it
normal: air conduction > bone conduction
conductive deafness: bone conduction > air conduction
sensorineural deafness: conduction diminished (they will stop hearing much earlier), but air still > bone
Vestibular system
triggers head + eye moments to provide retina with stable visual image
triggers adjustments in posture to maintain balance
SCCs (ant, post + lat) detect angular head acceleration
matched with corresponding coplanar ducts on other side-> sense movement of head in all planes
detected by hair cells with specific cilia
depol or hyperbole depending on what direction they are moved in
otoliths detect linear acceleration
utricle detects horizontal acceleration
saccule detects vertical acceleration
= calcium carbonate crystals inside a gelatinous mass (hair cells embedded here)
sensory epithelia
angular = crista ampullaris
vertical = macula sacculi
horizontal = macula utriculi