The Auditory System Flashcards
air particles
vibrate back and forth
rarefied air vs compressed
packets of less dense air vs dense air
creates sound wave
frequency
number of compressed or rarefied patches of air that pass ear each second , Hz
peak - rarefied
trough - compressed
intensity
air pressure difference between peaks and troughs, dB
small difference = low intensity
range of human hearing
20Hz - 20,000Hz 4,000Hz = best frequency thresholds high risk e.g. rock connects = 120dB pain e.g. gun shot = 140dB
anatomy of auditory system
outer ear - pinna and tympanic membrane
middle ear - tympanic membrane to oval window - air filled compartment
inner ear - oval window to cochlea and vestibular system
pinna
bit you can see
localises sound in vertical plane
tympanic membrane
ear drum
vibrates with sound waves - causes movement of ossicles
oval window
moves back and forth with ossicles
cochlea and vestibular system
cochlea - fluid filled, contains tranducers
ossicles of middle ear
malleus - hammer, attached to tympanic membrane
incus - anvil, rigid connection with malleus
stapes - stirrup, flexbile connection with incus, attaches to oval window
how does middle ear transfer sound?
middle ear takes large SA sound from tympanic membrane and converts to small SA on oval window - concentrates force of each sound eave
why concentrate sound in middle ear?
we live in air filled environment, ear is fluid filled, it is more difficult fo waves to move through fluid so need to concentrate them so no energy is lost as it moves through
if soundwave pushes inwards…..
bottom of maleeus moves down
point of incus pushes forward and pushes stapes into oval window = causes fluid movement along cochlea
round window
in cochlea
allows fluid to push out, reduces resistance
if sound pulls outwards…..
tympanic membrane moves out
malleus moves uo
incus pulls back
pulls stapes out with oval window
anatomy of cochlea
oval window joins at bottom and causes movement of fluid up to apex
meets helicotrema where fluid moves into different compartemtn back on itself
each spiral of cochlea has 3 compartments
scala vestibular
scala tymani
scala media
scala vestibular
fluid intially pushed through from oval window
filled with perilymph - extra cellular fluid
scala tympani
connects to round window
filled with perilymph
scala media
filled with endolymph - high K, only found in inner ear, high potential
path of fluid in cochlea
move up through vestibular - hit helicotrema - move down through tympani
organ of corti
runs along spiral, from base to apex, contains transducers that sit on basilar membrane
basilar membrane
runs along coil of cochlea
hair cells sit on top
tectorial membrane sits on top of hair cells
hair cells
3 rows of outer hair cells
1 row of inner hair cells
all have stereo cilia - move back and forth with fluid movement
each haiir cell has 3 rows of cilia in staircase
inner hair cell
primary tranducer
hair bundles surrounded by endolymph
cell body = perilymph
anatomy of basilar membrane
different properties depending where it is
at basal end - high freq sound smake membrane move more
at apex - low feq make membrane move
creates tonotopic map
basal = stiff, thick, narrow
apex = wider and less stiff
how does basilar membrane affect hair cells?
if stapes is pulled out….
fluid moves out
membrane pushes upwards, tectorial membrane moves and pushes stereocillia towards tallest one = depolarisation
how does basilar membrane affect hair cells?
if stapes moves in….
membrane moves in
hair cells move towards smallest one = hyper polarised = no signal down auditory nerve
hair bundles
connected by tip links - pull open channels for transducing
broken tip links—-> noise induced hearing loss
at top of shortest cilia = mechanoelectrical transducer channel
pushing towards tallest - opens channel - K moves in
if cilia push towards tallest
stretched tip link
channels open and K floods in
depol of hair cells - moves to base of cell
opens voltage gated Ca channel and Ca floods into cell
causes exocytosis of glutamate vesicles
actiavtes afferent neuron
if cilia push towards smallest
tip link shortens shuts channel - no K hyperpolarised Ca channels dont open no action potential
outer hair cells
electromotive act as cochlear amplifiers 'dancing hair cells' make inner cell responses bigger - can hear at lower intensities amplify basilar membrane movement
