CSD 306K Lecture Notes - Lecture 8: Temporal Lobe, Vestibulocochlear Nerve, Hair Cell

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(Look%at%structure)
Auditory%Canal%&%Meatus
Meatus%means%opening%and%this%is%the%opening%in%the%skull,%in%bone.%Little%hole%going%
inward
Where%auditory%canal%goes%through
Oil%glands%in%outer%1/3%of%canal;%cerumen%(wax)%serves%as%protection%and%
lubrication;%scent%is%repellent%to%insects
Hair%follicles%help%reduce%dust%&%wax%build-up
When%you%remove%wax,%you%are%at%more%risk%for%mold%to%grow%in%your%ear
Tympanic%Membrane
Round,%opaque,%concave,%cone%shaped
Drum-like%in%that%skin%in%stretched%across%an%opening
If%you%tear%this,%you%can%either%not%hear%anything%or%you%could%hear%a%sound%that%
sounds%like%a%blown%out%
Can%only%see%this,%if%we%shine%a%light%on%it
(first%picture%is%a%healthy%TP,%if%we%remove%the%TP%look%at%second%picture)
Middle%Ear
(fit%on%a%dime)%three%smallest%bones%in%the%human%body%and%is%where%all%human%
hearing%is%revolved%around
Ossicular%Chain:%%Consists%of%three%tiny%bones
Malleus-- connected%to%the%tympanic%membrane%and%the%incus
Incus-- connected%to%the%malleus%and%stapes
Stapes-- moves%in%and%out%of%the%oval%window
Middle%ear%can%fill%with%fluid%when%you%have%a%middle%ear%infection
If%this%area%is%filled%with%liquid,%your%hearing%will%not%sound%the%same
Can%affect%your%hearing%if%not%from%fluid%or%it%moving%to%other%parts%of%the%
ear%
When%you%pop%your%ear,%you%are%allowing%pressure%quality%because%you%
open%the%Eustachian%tube%and%the%ear%which%are%connected
Eustachian%Tube%
Also%auditory%tube%or%pharyngotympanic%tube%
Tube%that%connects%the%air-filled%middle%ear%cavity%to%an%opening%in%the%upper,%
back%portion%of%the%throat,%allowing%air%to%come%into%the%cavity
Inner%Ear
Vestibular%System
Semicircular%canals:%sense%of%balance
Vestibule:%sense%of%balance
Auditory%System
Cochlea:%sense%of%hearing
Cochlea%
The%cochlea%is%like%a%coiled%tube,%approx.%35%mm%in%length
Coils%in%on%itself%and%turns%about%2.75%times,%rotating%around%a%bony%axis%
called%the%modulus
Remember%it%is%a%labyrinth,%not%a%freestanding%structure,%within%the%bone
Responds%to%sounds%or%mechanical%wave/motion%that%the%sound%has%been%
transferred%from%the%Tympanic%Membrane
Inner%ear:%organ%of%hearing
Osseous%(bone)%labyrinth
Motion%detection:%vestibule%and%semi-circular%canals
Sound%detection:%cochlea
-
Membranous%labyrinth%(cochlear%portion)
-
All%Connected,%fluid%built
Openings:
Oval%windows%
§
Round%windows
§
Partitions:
Reissner's%membrane
§
Basilar%membrane
§
Chambers:%
Scala%Vestibuli
Scala%media
Scala%tympani
Scala%media%-duct
Fluid%has%to%go%somewhere%so%it%pushes%on%the%front%window,%fluid%tight
Basilar%Membrane
Each%hair%follicle%in%your%ear%is%only%responding%to%one%frequency
Hair%cells%respond%to%where%the%frequency%is%in%the%basilar%Membrane
Separates%the%Scala%Tympani%from%Scala%Media
Moves%in%a%wavelike%manner
Loud%sounds%create%large%waves
Soft%sounds%create%small%waves
Tonotopic
High%pitches%are%at%beginning%
Low%pitches%are%at%the%end%of%the%basilar%membrane
Organ%of%Corti
Tonotopic%organization
Traveling%wave%-determined%by%amplitude%and%frequency%of%the%sound
-
Hair%cells
Outer%versus%inner%
§
Shearing%motion
§
Depolarization%-mechanically%gated%K+%channels%
§
Transduction%of%energy
(changing%of%energy)
-
Cranial%nerve%VIII%->%CNS%(primary%auditory%cortex%of%temporal%
lobe)
-
Tonotopically%organized
-
§
-
These%hair%cells%feed%and%attach%to%the%nerves%and%they%dump%enough%
neurotransmitter%to%the%brain%and%we%register%the%sound
You%have%to%have%enough%neurotransmitter%(loud%enough%and%long%enough)
Cranial%8th%nerve%is%the%auditory%nerve%and%this%needs%to%works%to%hear
More%common%to%have%cochlear%disorders%than%there%is%a%cranial%8th%nerve
8th%nerve%is%the%wire%connecting%to%your%brain%and%the%brain%is%the%only%thing%
that%could%comprehend%this%sound
Hair%cells%die%overtime,%for%everybody,%some%individuals%will%have%accelerated% death%of%
hair%cells
2/6
Monday,%February%6,%2017
8:57%AM
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