auditory system Flashcards by naimah j

what 3 sections is ear divided into

outer, middle and inner ear

each part has specific function

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where is ear organ located

embedded in petrous portion of temporal bone - hardest bone in body

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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

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where does the middle ear begin

in tympanic membrane/eardrum

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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

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what are the smallest bones in the body

the ossicles: malleus, stapes and incus

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what is the hearing part of inner ear

cochlear

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what is the function of inner ear in hearing

transduce vibrations into nerve impulses

- produces a frequency(/pitch) and intensity(/loudness) analysis of sound

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what are the 3 compartments contained in cochlea

scala vestibuli and scala tympani and scala media

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what are the scala vestibuli and scala tympani

bone structures which contain perilymph

- high in sodium

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what is the scala media

membranous structure - contains endolymph (high in potassium)
where hearing organ/ organ of corti is located

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what is the basilar membrane

structure where organ of corti lies

arranged tonotopically - sensitive to different frequencies at different points along its length

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explain the organ of corti

contains 1000s of inner and outer hair cells

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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

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what is the role of inner hair cells

carry 95% of afferent information of auditory nerve
function = transduction of sound into nerve impulses

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what is role of outer hair cells

carry 95% of efferents of auditory nerve
function = modulation of sensitivity of response

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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

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what are the hairs on hair cells called

stereocilia

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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

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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

cycles per second

perceived tone

what is amplitude/loudness

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