lecture 8- auditory system Flashcards
how do the ear drums move during hearing
move in one direction
what are the 4 parts of sound encoding
frequency- number of sound wave cycles per second
intensity- amplitude of wave from peak to peak
onset- start, allows localisation of sound
duration
where does the auditory pathway start
cochlear
describe the structure of the scala vestibuli and the scala tympani
contain perilymph
low K+
Normal Ca2+
high Na+
describe the structure of the scala media
contain endolymph
high K+
low Ca2+
Low Na+
+80mV
where are sensory hair cells located
organ of corti
what kind of gradient is there between the scala media and organ of corti
electrical gradient of 140mV
what is characteristic frequency
specific frequency at which an auditory neuron or hair cell is most responsive.
describe the structure of the basilar membrane
base is narrow and stiff
apex is wide and floppy
describe the differences between high and low frequency sound stimulation
high- travels less far along BM
short wavelength
low energy
maximal movement (CF) at base
doesnt travel far
low- travels further along BM
long wavelength
high energy
maximal movement(CF) at apex
travel further
what is the CF location determined by
the width/stiffness of the basilar membrane
describe the tonotopic organisation of the inner hair cells
each IHC encodes a narrow frequency band
the position of the activated IHC encodes sound frequency
the brain then interprets the position of the active IHC as a specific sound frequency
is the neural firing rate used to encode sound intensity or sound frequency
sound intensity
where are the sensory hair cells found
organ of corti
what is the role of the inner hair cells
primary sensory receptors
encode auditory info and pass onto nerve fibres
what is the role of outer hair cells
amplify and sharpen sound perception
describe the structure on an inner hair cell
top contains hair bundle- stereocilia with met channels on top and tip links linking them all together
voltage gated calcium and potassium channels
afferent nerve fibres
what is a hair bundle
mechanosensitive ion channels at tips of shorter stereocillia
what happens when tension is applied to tip links
MET channels are pulled open
what occurs in a IHC at rest
1) slight tension on tip links
2) K+ enters down large electrical gradient through MET channels
3) this creates chemical gradient for K+ to exit
What is the resting potential of an IHC
-55 mV
what occurs in an IHC when excitation occurs
1) increased tension
2) MET channels open so larger current
3) Depolarisation (Ca2+ enters and vesicle release)
4) K+ and Ca2+ channels activated
do excitatory IHCs produce graded potentials or action potentials
graded
what occurs in an IHC when inhibition occurs
1) Deflection of hair bundle
2) MET channels close
3) hyperpolarisation below resting
How is K+ used for depolarisation and repolarisation on IHCs
dep- influx from endolymph, down electrical gradient
rep- efflux into perilymph, down chemical gradient
Describe the structure of an OHC
v shaped hair bundle (similar to IHC)
has K+ channel
contains prestin which is responsible for OHC electromotility
what occurs in an OHC at rest
resting MET current
resting potential 40mV
what occurs in an excitatory OHC
depolarisation, they shorten
what occurs in an inhibitory OHC
hyperpolarisation, they lengthen due to prestin relaxing
what does movement of the OHCs do to the basilar membrane and what does this mean
increase displacement
this amplifies positive feedback at the CF region
