Auditory System Flashcards
includes anatomy and physiology, audiometic testing, audiogram, and tympanometry
peripheral auditory nervous system
outer, middle, inner ear
central auditory nervous system
cochlear nucleus to primary auditory cortex
outer ear
acoustic process
outer ear components
- pinna
- external auditory meatus
- terminates at tympanic membrane (eardrum)
- cerumen (earwax)
pinna
sound localization
external auditory meatus
- sound amplifier
- ear canal
- open at 1 end/closed at other
cerumen
- earwax
- traps and repels
- protects ear from foreign items
outer ear: function
resonator and amplifier
middle ear
mechanical process
middle ear components
- tympanic membrane
- ossicular chain
- middle ear muscles
- eustachian tube
tympanic membrane
layers:
1. epidermal
2. fibrous
3. membranous
ossicular chain
- malleus
- incus
- stapes
middle ear muscles
- stapedius (CN VII)
- tensor tympani (CN V)
eustachian tube
- valve-like
- opens to equalize pressure
middle ear function
conduction, protection
inner ear
hydromechanical, chemical process
inner ear components
- temporal bone
- cochlea
- basilar membrane
- organ of corti
temporal bone
petrous portion
cochlea
- osseous bony cochlea
- membranous cochlea
organ of corti
- outer hair cells
- inner hair cells
outer hair cells
3-5 rows, 12,000 cells
inner hair cells
single row, 3,500 cells
inner ear function
converts mechanical sound waves to electrical activity and neural impulses
auditory nerve CN VIII
- neural process
- transmits auditory and vestibular information from ear to brain
- spiral ganglion: collection of auditory nerve fibers
auditory cortex
- within the cerebrum at highest level
- temporal lobes (bilaterally)
- Heschl’s gyrus: all information reaching cerebrum from lower pathways arrives first at the primary auditory cortex
audiometry
testing that measures the range and sensitivity of an individual’s hearing
pure tone testing
air conduction testing
air conduction testing
sounds go through outer and middle ear
pure tone testing: frequencies tested
250, 500, 1000, 2000, 4000, and 8000 Hz
pure tone testing: presentation
headphones, external
pure tone testing: response modes
- adults: raise hand, push button, etc.
- children: visual reinforcement, startle response, play audiometry
pure tone testing: identify threshold
use method down 10 dB, up 5 dB
air conduction masking
when air conduction threshold in one ear exceeds bone conduction threshold in contralateral ear by 40 dB HL or more
bone conduction testing: tonal stimuli
sound through bone vibration direct to cochlea/inner ear
bone conduction testing: frequencies tested
500, 1000, 2000, and 4000 Hz
bone conduction testing: presentation
bone oscillator behind the ear instead of headphones
auditory brainstem response (ABR)
used with children who can’t complete a normal hearing screen and/or if hearing loss is suspected in the brain/brain pathway
audiogram
graphic display of hearing test
audiogram: threshold
intensity at which signal is barely detectable 50% of time
audiogram: identifies
type, degree, and configuration of hearing loss
audiogram: frequency range
125-8000 Hz
audiogram: intensity range
-10-110 dB HL
otoacoustic emissions (OAEs): testing
used to determine hair cell function
otoacoustic emissions (OAEs): presentation
- earphone/probe inserted into ear (that makes sounds)
- OAEs record the response to that sound by vibration
frequency limits
- 16 Hz-20,000 Hz
- most sensitive to mid frequency 500-4000 Hz
Carhart’s notch
dip in audiogram at 2000 Hz to stapes fixation
pure tone average (PTA)
average of 500, 1000, and 2000 Hz thresholds
Fletcher average
- if sharply sloping loss, use fletcher average
- average of the 2 best thresholds at 500, 1000, and 2000 Hz
type of hearing loss
- identifies the site of damage of the auditory system
- conductive, sensorineural, and mixed
degree of hearing loss
- refers to the severity of the hearing loss
- normal, slight, mild, moderate, mod-severe, severe, profound
configuration of hearing loss
- refers to the extent and pattern of loss across frequencies
- flat, rising, sloping, low frequency, high frequency, precipitous
conductive hearing loss
- outer and middle ear
- air-bone gap greater than 10 dB
- bone threshold within normal limits (sounds cannot get through outer and middle ear)
sensorineural hearing loss
- inner ear and/or CN VIII
- air + bone thresholds are equal
- both display a hearing loss (inner ear damage/problems with nerve pathways)
mixed hearing loss
combination of sensorineural hearing loss and conductive hearing loss components
degrees of hearing loss: -10-15 dB
normal
degrees of hearing loss: 16-25 dB
slight
degrees of hearing loss: 26-40 dB
mild
degrees of hearing loss: 41-55 dB
moderate
degrees of hearing loss: 56-70 dB
moderately severe
degrees of hearing loss: 71-90 dB
severe
degrees of hearing loss: 91+ dB
profound
configuration of loss: flat
AC thresholds within 20 dB of each other
configuration of loss: rising
AC thresholds for low frequencies at least 20 dB poorer than for high frequencies
configuration of loss: sloping
AC thresholds for high frequencies at least 20 dB poorer than for low frequencies
configuration of loss: low frequency
hearing loss only found in the low frequencies
configuration of loss: high frequency
hearing loss only found in the high frequencies
configuration of loss: precipitous
high frequency thresholds worsen by at least 20 dB per octave
tympanometry
measurement of eardrum immittance as a function of air pressure in the ear canal
tympanometry: procedure
a soft rubber tip (probe) is inserted into the ear canal, changing the pressure in the ear canal
tympanogram
the resulting graph is a tympanogram
tympanogram measures
- static admittance
- tympanic peak pressure
- tympanic width
- canal volume
static admittance
- the admittance of the middle ear system (mobility)
- height of peak
- higher is more mobile
tympanic peak pressure
the point at which air pressure is equal on either side of tympanic membrane
tympanic width
describes the steepness and shape of the slope of the tympanogram, near the peak
canal volume
estimates volume of the air medial to the probe
tympanogram types
- type A
- type As
- type Ad
- type B
- type C
tympanogram: type A
normal
tympanogram: type As
- shallow compliance
- reduced peak height, normal pressure
- indicates: middle ear fluid, otosclerosis
tympanogram: type Ad
- deep compliance
- greater than normal peak height, normal pressure
- indicates: ossicular disarticulation, TM scaring
tympanogram: type B
- flat: no pressure or compliance
- no discernible peak shown (NP = no peak)
- indicates: middle ear effusion, perforated TM, cerumen occlusion
tympanogram: type C
- negative pressure
- any height, normal mobility
- indicates: negative pressure TM or middle ear, eustachian tube dysfunction