auditory system Flashcards
what 3 sections is ear divided into
outer, middle and inner ear
each part has specific function
where is ear organ located
embedded in petrous portion of temporal bone - hardest bone in body
what are the functions of outer ear/pinna and external acoustic canal(meatus)
- capture sound and focus it on tympanic membrane
- amplify some frequencies by resonance in canal
- protect ear from external threats
where does the middle ear begin
in tympanic membrane/eardrum
main function of middle ear
amplification by focusing vibrations from large to smaller surface area(oval window). change in surface area means pressure is increased.
- using leverage from incus stapes join to increase force on oval window
what are the smallest bones in the body
the ossicles: malleus, stapes and incus
what is the hearing part of inner ear
cochlear
what is the function of inner ear in hearing
transduce vibrations into nerve impulses
- produces a frequency(/pitch) and intensity(/loudness) analysis of sound
what are the 3 compartments contained in cochlea
scala vestibuli and scala tympani and scala media
what are the scala vestibuli and scala tympani
bone structures which contain perilymph
- high in sodium
what is the scala media
membranous structure - contains endolymph (high in potassium)
where hearing organ/ organ of corti is located
what is the basilar membrane
structure where organ of corti lies
arranged tonotopically - sensitive to different frequencies at different points along its length
explain the organ of corti
contains 1000s of inner and outer hair cells
what is the tectorial membrane
located above hair cells and allows their deflection - in turn depolarise the cell
only outer hair cell are in constant contact with tectorial membrane - assist contact with ihc
what is the role of inner hair cells
carry 95% of afferent information of auditory nerve function = transduction of sound into nerve impulses
what is role of outer hair cells
carry 95% of efferents of auditory nerve function = modulation of sensitivity of response
why are outer hair cells able to contract
have protein in membrane and can change length - makes tectorial membrane closer or away from inner hair cell
what are the hairs on hair cells called
stereocilia
explain how transduction occurs
deflection of stereocilia towards longest cilium will open k+ channels
ionic interchange depolarises cells
calcium come in via vgcc
neurotransmitter is liberated
what does greater deflection of stereocilia and k+ ion channel opening cause
higher amplitudes (louder) sounds
what hair cells allow you to hear softer sounds
outer hair cells
what is the auditory pathway
spiral ganglions from each cochlea project -> via audiovestibular nerve to ipsilateral cochlear nuclei (monoaural neurons)
some auditory info crosses at -> superior olive level
after this point all connections are bilateral
-> inferior colliculus
-> medial geniculate body
what is frequency/pitch
Hz
cycles per second
perceived tone
what is amplitude/loudness
dB
sound pressure
subjective attribute correlated with physical strength
what is the human range of hearing
freq - 20 - 20000 Hz
loudness - 0dB to 120dB
why is the decibel scale useful
range of sensitivity is very large
how doe shearing acuity change with age
decrease with age, particularly higher frequencies
what are the aims of hearing assessmentI
is there hearing loss?
what type
of what degree
what is a tuning fork used for
used to establish probable presence or absence of hearing loss with significant conductive component
- used to provide early and general info and - when audiometry not available
what is pure tone audiometry
science of measuring hearing acuity in sound intensity and frequency
uses audiometer
what is an audiometer
device used to produce sound of varying intensity and frequency
what is an audiogram
graph where hearing thresholds are plotted to define hearing loss or not
normal = 0-20dB
what is the central processing assessment
assessment of hearing abilities other than detection
e.g sound localisation, filtered speech and speech in noise
uses verbal and non verbal tests
what is tympanometry
examination used to test condition of middle ear and mobility of eardrum and conduction bones by creating variations of air pressure in air canal
what are otoacoustic emissions
normal cochlea produces low intensity sounds called OSEs - produced specifically by outer hair cells as they expand and contract
test is often part of newborn hearing screening and hearing loss monitoring
what are auditory evoked potentials
electrocochleography - electrical activity from cochlea and 8th nerve. evoked by clicks and tone burst
abr - electrical activity from 8th nerve and brainstem nuclei and tracts
late responses - electrical activity from auditory and association cortex
what is abr
electrical responses from auditory pathway
does not require attention
commonly used in babies and children
when would cortical potentials be useful
could be affected on neurological conditions or processing problems
what is conductive hearing loss
problem is located in outer or middle ear
what is sensorineural loss
problem in inner ear or auditory nerve
what is mixed hearing loss
conduction and transduction of sound are affected
what does degree of hearing loss depend on
hearing thresholds
what are some causes of conductive hearing loss
wax
foreign body
otitis
otosclerosis
what are some causes of sensorineural loss
presbycusis - loss with age of hair cells
ototoxicity
8th nerve tumour
treatment for hearing loss
treat underlying cause
hearing aids
cochlear implants
brainstem implants
what do hearing aids do
amplify sounds
how do cochlear implants work
replaces function of hair cells by receiving sound analysing it, transforming into electrical signals and sending an electric impulse directly to auditory nerve
needs functional auditory nerve to function*
how do brainstem implants work
electrical signals can be sent to set of electrodes placed in brainstem
very risky - advised only for bilateral auditory nerve damage
