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53 terms

More Middle Ear

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what is the ratio of impedence of cochlear fluid and air?
4000:1
w/o the ME, how much sound would be reflected back? (% and dB)
99.9%
30-35 dB
w/o the ME, how much energy would be lost?
30-35 dB
How does the ME overcome the impedence mismatch?
1. areal ratio (17:1)
2. curved membrane ratio (2:1)
3. ossicular lever ratio (1:3:1)
how big is the part of the TM that vibrates?
55mm
what is the areal ratio?
17-1 (so, pressure is amplified 17 times from TM to footplate)
what is the area of the footplate?
3.2mm
Total transmission ratio of the ME
46:1 (46 times more pressure ant footplate than at TM)
=33 dB gain
how much hearing loss CAN the ME cause i it is sick or absent
40-60 dB conductive hearing loss
does a normal ME have impedence?
yes
at 80-90 db, stapedius and tensor tympani have what?
bilateral, consensual reflexive contraction
-they attenuate sound by 10-30 dB
what does the tensor tympani reflex in reaction to?
puff of air in eye
bc od CN V
ME pathologies
1. otosclerosis
2. ossicular disconinuity
3. frozen ossicular chain
otosclerosis
-increases impedance
-begins with vascular spongiosis, eventually replaced with sclerotic plaques
-stapes becomes fixed in oval window
-an early sign is Schwartze's sign (bluish-red tint near promontory due to increased vascularization)
-characteristic notch at 2000 Hz (carhart's notch)
ossicular discontinuity
-broken ossicular chain
-causes decreased impedance
TM can vibrate freely
-trauma
frozen ossicular chain
increased impedance
What part of the temporal bone is the inner ear located in?
petrous portion
3 parts of the inner ear
1. cochlea
2. vestibule (utricle/saccule)
3. semicircular canal
Bony labyrinth
canals through temporal bone
-lined by membranous labyrinth
how many turns does the cochlea take?
between 2.2-2.9 turns
what are the measurements of the cochlea?
1 cm wide
5 mm from base to apex
modiolus
central core of cochlea that eventually becomes CN VIII (has nerve fibers from the hair cells and blood vessels)
osseus spiral lamina
-shelf-like structure that winds around the modiolus
helicotrema
apex of the cochlea where the two scalas meet
where is the oval window?
at the opening of the scala vestibuli (the most superior duct)
round window is located
-at the basal-most aspect of the scala tympani (most inferior duct)
reissner's membrane separates
separates scala media from scala tympani
basilar membrane separates
separates scala media from scala vestibuli
ductus reuniens of hensen
how scala media communicated w/the vestibular portion of the inner ear (at the basal region)
what does the stria vascularis do?
produces endolymph
how is the basilar membrane shaped?
narrower and stiffer at base, wider at apex
25-35 mm
what is embedded in the tectorial membrane?
tips of OHC cilia
reticular lamina
-is ceiling of organ of corti
-separates endolymph from cortilymph (similar to perilymph)
-cilia penetrate the reticular lamina so they can bathe in endolymph (the rest of the hair cell bathes in perilymph)
OHCs are best for hearing________
less intense sounds
IHCs are best for hearing ____________
louder (more intense) sounds
How many rows of hair cells are there?
3-5 rows OHCs
1 row IHCs
How many hair cells are there?
12,000 OHCs
3500 IHCs
How are hair cells shaped?
OHC=test-tube shaped
IHC=flask-shaped
what is the electrical charge of hair cells?
OHCs= -60 mV
IHCs= -40 mV
are IHC stereocilia embedded in the tectorial membrane?
no, only OHC stereocilia are embedded
5% of all auditory nerve fibers serve the
OHCs
95% of all auditory nerve fibers serve the
IHCs
the cell bodies of the OHC and IHC neurons comprise the ______________
spiral ganglion of the primary auditory neuron
the IHCs have less__________connectivity
efferent
efferent fibers emanating from superior olivary complex in brainstem=
olivo-cochlear bundle
what is the electrical charge of endolymph?
+80 mV (high potassium)
what is the electrical charge of perilymph?
low potassim
vestibular (endolymphatic) aqueduct
-contains endolymph
-from vestibule to endolymphatic sac
-helps regulate endolymphatic pressure to over or under-absorb endolymph
cochlear aqueduct
-contains perilymph
from basal cochlea (scala tympani) to subarachnoid space
-allows transfer of CSF
what is non-patent by age 50 in 50% of people?
cochlear acqueduct
scala vestibuli and scala tympani are filled with__________
perilymph
scala media is filled with__________
endolymph
organ of corti is filled with__________
cortilymph (like perilymph)