Audiology Flashcards
what is the pinna made up of
helix fossa concha EAM tragus lobule antitragus antihelix antihelical fold scapha
resonance adult ear canal
2.5-3kHz
resonance child ear canal
7kHz
cone of confusion
area in which binaural cues (phase and transient disparities) are useless for sound localisation
law of the first wave
primary sound wave used to determine location
duplex theory of sound localisation
ITD and IID used to locate sound
layers of the TM
epidermis
lamina propria
mucosa
pars tensa
all three layers, makes up 85% of TM
pars flaccida
no lamina layer, 15% of TM
axial ligaments and tendons in middle ear
anterior malleal ligament posterior incudal ligament tensor tympani tendon stapedial tendon annular ligament
middle ear protection mechanism
high intensity low frequency sound
above 80dBSL
reduction of 0.6-0.7dB per dB over sensation level
2000Hz or below
tensor palatini
opens and closes eustachian tube
immittance
impedance and admittance
admittance
energy flowing through the system
impedance
energy flow opposition
afferent pathway
cochlea cochlear nucleus SOC lateral lemniscus inferior colliculus medial geniculate body A1
auditory nerve
myelinated fibres - inner hair cells
unmyelinated fibres - outer hair cells
cochlear nuclei
1st major nuclei in path
anteroventral, dorsal, podterovental areas
SOC
in pons
MSO, LSO, MTB areas
first part to receive bilateral information
lateral lemniscus
ventral and dorsal nuclei
inferior colliculus
in brainstem/ mid brain
central nucleus, dorsal cortex, paracentral nuclei
MGB
afferent inputs from IC
ventral, dorsal and medial divisions
descending pathway
cortex MGB IC Lateral lemniscus SOC cochlear nucleus cochlea
influences the information reaching the brain
Right posterior superior temporal gyrus
perception of sound
corticofugally controlled corticopetal-corticofugal loops
early filter
increase SNR
auditory filters
determines Hz selectivity of cochlea and sound discrimination
outer hair cell motility
displace basilar membrane
moves membrane at resonant place = cochlear amplifier
driven by prestin
habenula perforata
myelinated portion of auditory nerve
place theory
helmholtz
tonotopicity through system
if we know where the nerve fired we can determine the signal frequency
temporal theory
wever & bray
nerves discharge at rates proportional to soundwave
up to 1000Hz
higher frequency (staggered firing - volley)
Volley principle
wever & bray
nerve responds at peak of waveform
different nerve fire in successive cycles
helicotrema
scala tympani and vestibuli communicate here
cochlea
houses organ of corti base high Hz apex low Hz 2 3/4 turns 35mm long divided by osseous lamina
modiolus
central axis of cochlea
reissner’s membrane
divides scala media and vestibuli 2 layers epithelial mesothelial squamous cells linked by tight and adherens junctions
basilar membrane
divides scala media and tympani
varies in thickness and width
apex wider, flexible, thin, low Hz
base less wide, stiff, thick, high Hz
Desomosomes
connects basilar membrane to border cells
strong connections which resist shearing
temporal bones
squamous
tympanic
petrous - inner ear here
vestibule
ultricle and saccule
striavascularis
rich blood supply o2 to cochlea metabolic control battery for cochlea gives endolymph positive charge pumping mechanism of K+
bones
incus
stapes
malleus
area motor
prestin
outer hair cells
stria side rows of three to four stereocillia shaped like a W long and cylindrical electromotility from prestin deiter support cell at bottom amplify low level sounds
inner hair cells
modiolus side
single row
stereocillia shaped like a U
depolarise when stimulated generate AP
deiters cell
cup bottom of outer hair cell
provide support
actin and tubulin skeleton
ribbon synapse
specialised cell
glutamatergic
glutamate vesicles attached to surface by filamentous tethers
aka. dense bodies (inner hair cells)
receive graded information about incoming stimulus
inner hair cell innervation
many to one innervation myelinated fibres radial fibres thick more fibres than hair cells type 1
outer hair cell innervation
one to many innervation type 2 outer spiral fibres unmyelinated synapse with many hair cells
modes of transfer
EAM - air
Middle ear - mechanical
inner ear - mechanical, hydrodynamic, electrochemical
nervous system - electrochemical
impedance mismatch
2 mediums different impedance, some reflected, some transmitted
interaural time / phase difference
sound on one side of head
difference in time taken to get to each ear, means signal will reach each ear at a different phase
interaural intensity / level differences
sound one side of head
sound level in each ear differs
noticed more in high Hz
hearing loss thresholds
mild 20-40dB
moderate 41-70dB
severe 71-95dB
profound 95+dB
OME
no air exchange due to eustachian tube dysfunction
retracted ear drum
air trapped in TM is absorbed by mucosal membranes
causes negative pressure resulting in a transduction of fluid into middle ear
some water reabsorbed causing glue like fluid
grommets, drainage, hearing aids, autoinflation
colds and barometric changes
otosclerosis
abnormal bone growth stapes fixation to footplate genetic conductive/mixed hearing loss - progressive, bilateral and asymmetrical tinnitus, otalgia, vertigo Carhart's 2kHz notch Schwartze sign - redness of TM
surgery, hearing aids, sodium fluoride
presbycusis
age related hearing loss
high frequency loss - bilateral, symmetrical
hearing aids
Acoustic Neuroma
aka. vestibular schwannoma - tumor of schwann cells covering vestibular nerve
asymmetrical SNHL
unilateral tinnitus - can be only symptom
vertigo, bell’s palsy, poor limb coordination
ABR, CT, MRI, speech testing
ABR = waves 1, 2, 5 - increase latency
MRI monitoring, gamma knife radiation (can cause hydrocephalus), hearing aids, surgery
types of presbycusis
sensory
metabolic
neural
