The auditory pathway, hearing and hearing loss Flashcards
- what is sound and what are Frequency and pitch
sound- Longitudinal pressure wave travelling through air or other medium
Frequency- Pitch of sound, Measured in Hertz (Hz) cycles per second
Amplitude (intensity)- Loudness, Measured in dB (decibels)
What are the range of sound pressures humans can hear in
20Hz- 20KHz
what is the amplitude that causes damage to human hearing in dB
at what Db is normal conversational level?
at what Frequencies are humans most sensitive to sound
Humans are most sensitive between 2-5 KHZ and given sound pressures (dB)
How many of each hair cell are there
what type of nerev fibres from VIII cranila nerve fibres go to each type of hair cells
95% of nerve fibres are type 1 and go to inner hair cells- each type 1 fibre is associated with one inner hair cells
5% are type II outer hair cells- outer hair cells
make contact with several OHCs
type 1 nerve fibres have limited frequency range- producing a tuning curve Why?
What will happen to the tuning curve if you damage Type 2 nerve cells? and subsequent hearing
tuning curve shifts upwards
Will become Less sensitive to sounds as will loose the OHC amplifier- this affects sound interlligility of speech
Explain how if each indiviudal nerve fibres has selected limited frequency we can hear sucha wide range
over 30K nerve fibres- cover wide range of frequencies- some overlap-
Describe coding sound frequency- ‘place code’
Auditory system keeps tract of where information originated on basilar memebrane- mapped withing processing centres on the surface of auditory cortex
Tonotopic organisation (tonos-sound) (topos-place)
fibres when they leave the cochlear travel to the cochlear nucleus in the brain
Low frequency (apex of cochlear)—-> anteriro cochlear nucleus
high frequency (base of cochlear)- posteiro chcolear nucleus
Describe coding sound frequency- Place code
firing of AP- in auditory enrve firbes synchrosies with peaks in sound wave
Phase locking
time between AP- tells you frequency of sond
only occurs for low Frequency sounds
With pahse locking why dont we get Action potential on all wave form peaks
- each inner nerve cell has at leats 10 type 1 nerve fibres associated
- so even if one of 1Type nerve fibres misses it - one of the other nerve firbes will detetc it
- brain able to organise into faithful representation of sound waveform
Name the human auitory pathway
cochjlear
auitoruy nerve
Ventral cochlear nuclus (contralteral)
superiro olivary complex
infeiror colliculus
medial geniculate body
autiroryd cortexc
Pre-dominantly nerve fibres are contralteral
Where is the auditory cortex located?
hidden intact structure
part oif the superiro temporal lobe
in the sylvian fissure in order to see- Primary audiotry cortec- Herschl’gyris
Describe areas of the brain where damage can result in dysphasia (deficits in spech ) for receptive and expressive
Receptive- Wernickes area
Expressive- Brocas area
(both along superiro temporal gyrus
Describe localsiation for interaural tiem difference for Low frequency sound s- below 1500Hz
Path difference
sound arrives at one ear faster than the other
phase differences.
describe how the brain localises high frequency sounds- interaural intensity differences- higher Frequency sounds >1500 Hz
the head is a solid object- Sound shadow on the far side
describe the different levels of hearing loss 0-120 (normal- profound)
- 0-20dB normal rnage
- 20-40 mild hearing loss (impact on speach)
- 40-70 moderate
- 80-90 severe
- 90-120- profound
Describe the components of the cochlear implant
microphone and processor
induction coil
electrode array in cochlear (32)
more effecitve the early implantned- brain learns
