More Middle Ear

53 terms by AbraMarcum 

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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)

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