Auditory System Flashcards
Compartments of the ear
Outer - mechanical
Middle - mechanical and amplify
Inner - neuro
Cochlear duct
Houses hair cells and filled wiht endolymph
Surrounded by bony ducts (vestbular on top and tympanic on the bottom)
Sound path
Tympanic mmb Malleus Incus Stapes Oval window Through ducts to round rindow
Membranes
Basilar on bottom of cochlear separates from tympanic duct
Vestbiular on top of cochlear separates form vestbiular duct
Hair cells
K+ moves into open membranes to depolarize
Results in NT release
Also efferent compoennts that tunes
Cochlea location
In the petrous protion of the temporal bone
CN8 and 7 travle through internal auditory meatus to go to brainstem
Spiral ganglion
Cell bodies of the sensory bipolar neurons…sit in the organ of corit
Modiolus
Protects deep portion of the cochlea and spiral ganglion
Stria vascularis
Leaches endolymph into cochlear duct
Basilar membrane movement
Hair cells rub against tectorial membrane which depolarizes bipolar neurons
Frequency differentiation
Closer to oval window - higher freuqncy…rigid at base and higher freuqneyc sounds more attentuated by distance
Closer to apex - lower frequency
Pontomeduallary junction
Ventral cochlear nucleus contributes to sound localization…both unconscious (superior olive) and conscious (cortex)
Dorsal cochlear nucles…primarily to sound processes like sound discrimination (cortex)
Sound represented bilaterally but there is contralateral over-representation
Superior olive
Medial uses time difference for LF sounds
Lateral uses amplitude differences for HF sounds…nucleus of trapeoid body also involved
Dorsal acoustic fibers
Ascend in the lateral lemnicus to the inferior colliculus
Fibers from SO and NTB also ascend in lateral lemniscus
Dampening loud sounds
Both pathways originate in superior olive nucleus
Stapedius muscle from CN7
Tensor tympani from CN5
Midbrain
Fibers in lateral lemniscus synapse in the IC
Also a commisure of the IC…fibers pass from brachium of the IC to the medial geniculate nucleus of the thalamus
Thalamus and cortex
Fibers from IC synapse on MGN
MGN relays precise information to PAC
Fibers from MGN to PAC called auditory radiations
PAC and Wernick’s area
PAC - conscious sound detection and localization and discrimination…lower in lateral and higher in medial
Wernick’es - on left side…speech disrcimination
Types of conductive hearing loss
Otitis media
Tympanic membrane perforation
Otoscelrosis - bone growht between temorla bone and stapes…reduces mobility and therefore condcuton
Most form some kind of occlusion in middle ear
Sensory hearing loss
Damage to hair cells
Acoustic neuroma
Non-specific disorders
Tinnitus - could be any reason…even PTSD
Weber test
Bone conduction in each ear simultaneously
If louder in affected ear, then conductive
If quieter in affected ear, then sensory
Rinne test
Tests air conduction versus bone conduction in each ear
Hearing sound louder through bone suggests conduction loss in ear
Hearing sound louder through air in each ear but louder in one than other sugests sensory
Unilateral lesion of cochlea or CN 8
Unilateral deafness
Unilateral lesion of auditory pathway
PICA
Bilateral hearing reduction but not deafness
Unilateral cortical lesion
MCA lesion
Decrease in ability to consciously discriminate sounds
Wernicke leison
Inability to understand language
