lecture 11 - adrian rees Flashcards
sound travels by
rearefraction and compression of molecules
frequency of sound wave is described as…
pitch
amplitude is described as
loudness
the outer ear
the pinna
auditory canal
middle ear
ossicles (malleus, incus and stapes)
inner ear
cochlea
role of the pinna
helps to funnel sound into the ear canal
is also helps us localise sounds in the vertical plane
auditory canal conducts sound down to the
tympanic membrane
the auditory canal also causes…
acoustic gain due to resonance
the sound reaching the tympanic membrane causes the tympanic membrane to vibrate then it is transmitted through the
ossicles
what are the three ossicles
malleus, incus and stapes
the footplate of the stapes connects to..
a window in the wall of the cochlea and allows the vibrations to enter the cochlea
the middle ear pressure needs t be the same as the…
atmospheric pressure on the other side of the tympanic membrane
if the atmospheric pressure changes how does the middle ear equilibrate
via the eustachian tube (connects to the nasopharynx, when you swallow the eustachian tube opens and allows the air pressure to equilibrate)
the cochlea is ______ filled
fluid
the middle ear acts as an….
impedance transformer (improves transfer from 3% to 60%)
is the pressure greater at the tympanic membrane or the stapes
the stapes
this is because the area is smaller at the stapes and the force is the same (P = force/area)
the malleus is longer than the incus (they act as a lever) so we get a larger movement in the malleus and a smaller movement in the incus but with
greater force
lever ratio is 1.3 x and area ratio is 18 x so the total increase in pressure is 1.3 multiplied by 18 giving a
x 25 increase in pressure between the tympanic membrane and the stapes
each nerve fibre is selective for a limited range of…
frequency
what is the top compartment of the cochlea called
the scala vestibuli
what is the bottom compartment of the cochlea called
the scala tympani
what is in between the two compartments
scala media
coming away from the cochlea at all levels are cochlea nerve fibres and the ganglion (where the cell bodies are found) is a…
spiral ganglion which spirals around the cochlea
what is the membrane between the scala vestibuli and the scala media
reissner’s membrane
what is the membrane between the scala media and the scala tympani
basilar membrane
what structure sits on the basilar membrane
the organ of corti
what membrane over lies the organ of corti
the tectorial membrane
what fluid fills scala vestibuli and scala tympani
perilymph (high Na+)
what fluid fills scala media
endolymph (high K+)
there is a high conc of K+ in the scala media due to the epithelium called the…
stria vascularis which pumps potassium ions into the space
the stereocilia of the outer hair cells embed into the
tectorial membrane
the region in between the OHCs and IHCs is called the
tunnel of corti
the stapes footplate goes backwards and forwards making contact with the oval window (a window onto scala vestibuli) at the frequency of the sound and that increases the pressure in the scala vestibuli when it pushes in out decreases the pressure pulls out. The round window (in the wall of the cochlea) bulges out when the stapes pushes in and pulls in when the stapes pulls out to accommodate the pressure changes. the pressure applied pushes the basilar membrane down, a wave travels along the basilar membrane to the apex. the cochlea is stiffer and the base and floppier at the apex. the stiffer part will vibrate first and the apex later. the displacement of the basilar membrane depends on the frequency of the sound. A high frequency sound causes most displacement at the…
base
and a low frequency sound causes most displacement at the apex
