Hearing Flashcards
what is rarefaction
low amplitude sounds
what muscle is attached to the malleus
tensor tympani
what bone is in the oval window
stapes
where is endolymph found
scala media
semicircular canals vestibule
where is perilymph found
scala vestibuli, scala tympani
describe the pathway from vibrations to sound signals to the brain
- tympanic membrane
- 3 ear bones vibrate
- the stapes send vibration to the oval window which goes to the cochlear
- the fluid wave push onto the membranes of the cochlear duct
hair cells bend and release neurotransmitter - neurotransmitter release onto sensory neurones creates action potentials that travel thorugh the cochelar nerve
- energy from waves transfers across the coclear duct into the tympanic duct and is dissapated into the middle ear through the round window
describe the process of frequency detection in the cochlear
basilar fibres structure changes from short and stiff to long and floppy along the length of the cochlear
this means they have resonant frequencies that are graded along the cochlear with high frequency at the base and low at the apex
when the resonant frequency is activated it absorbs all the kinetic energy of the wave and effectively stops it
what is the organ of corti
the receptor organ for hearing
epithelial cells allows for transduction of auditory signals into nerve impulses due to movement of hair cells
describe the structure of the organ of corti
contains inner and outer hair cells
stereocillia project from the tops of hair cells
shortest hair cells in the outer rows and longest in the center
what does tonotopically mean
different frequencies of sound wave interact with different locations in the cochlea
name the structures found in the scala media
tectorial membrane
organ of corti
reissner’s membrane
describe the function of the organ of corti
upward deflection of the basilar membrane moves the inner and outer hairs laterally
most cochlear nerve endings terminate on the inner hair cells even though there are many less of them
mechanical activation as well as neuronal signals from the brainstem shorten and stiffen the outer hair cells
this tunes the cochlear by amplifying select frequencies
what is cochlear tuning
outer hair cells are stimulated by the basilar membrane to depolarise and contract.
this enhances the auditory signal at the centre of the standing wave and inhibits on either side like lateral inhibition
what structure in the brainstem is responsible for cochlear tuning
olive
this releases aCh onto the inner hair cells causing them to depolarise
this dampens down hearing for background noise
describe what happens when stereocillia are displaced
opens potassium channels in the cillia
this causes voltage gated calcium channels to open
calcium floods in which causes release of neurotransmitter
what happens when sensory hairs are displaced towards the tallest stereocillia
depolarisation causing an increase in action potential
what happens when sterecillia are displaced towards the shorter hairs
inhibition causing hyperpolarisation and fewer action potentials
however there is baseline activity alwars
describe the pathway of sound information from cn 8 to the brain
upper medulla (dorsal and ventral cochleal nucleus) first order fibres synapse here
some fibres travel ipsilaterally, but most contralaterally up to the inferior colliculus (synapses)
some fibres travel to the superior olivary nucleus
the fibres project to the medial geniculate nucleus of the thalamus where the fibres synapse and join the auditory radiation to the auditory cortex
signals travel to both brain hemispheres
where does sound go apart from to the auditory cortex
superior olives
reticulum of the brainstem
vermis of the cerebellum (arousal response to noise)
where is the auditory cortex
insula and temporal lobe
what nucleus projects to the primary auditory cortex
medial geniculate nucleus
what information does the auditory association cortex receive
secondary projections from the primary auditory area
and also thalamic association area
describe the mapping to the auditory cortec
the sound is mapped in the cochlear and this is preserved all the way to the cortex
lower frequencies are usually anterior
6 maps per person which are all involved in sound cognition
how does directionality occur (3 ways) horizontal only
volume
sound shadow
sound lag
how can the ear detect front to back or above/ below directionality
folds in the pinna which changes the characteristics of sound coming from above compared to below
what can cause conduction deafness
blockage in the outer ear
infection
angle of eustacian tube causes a predisposition to middle ear infections
can be caused by ossification of middle ear bones
ruptured tympanic membrane
what is sensineural deafness
caused by breakdown of cochlear or damage to nerve/ cortex
what is the effect of an association area lesion
loss of meaning of sound
what is the effect of a primary cortex lesion
reduced sensitivity to sound
what does a rinne negative (left ear) and ipsilateral weber test tell you
left conductive deafness
what does a contralateral weber tell you
left sensory neural deafness
