CNS/sensory 5 - auditory Flashcards
describe amplitude and frequency of sound
changes of pressure around head
auditory system detects changes in pressure
what are hertz
number of cycles per second = frequency = pitch
what is amplitude
Loudness
describe normal audibility curve
dB = 20log (sound pressure/reference pressure
20 change in db = 10 times louder
descrive frequency range of humans
~10khz
to 20 khz
human voice = 1-4khz
what is damage threshold
less than pain threshold
not just loudness but duration
Around 80db
what is presbycusis
adavancing age = loss of hearing at high frequencies (>1000hz)
what is external auditory cannal
pinna reflects pressure wave into it
what is pinna
folds = reflect certain frequencies of sounds into external auditory canal
what is middle ear
has 3 smallest bones in body
malleus, incus, stapes
connects tympanic membrane to another membrane on other side of ear
what is inner ear
in skull
what is cochlea
shell
what is eustachian tube
middle ear attached to back of throat through this
can hear in airplane - open mouth and equalize pressure in middle ear, also when have cold = inflammation and cannot regulate pressure well
what is tympanic membrane
strike eardrum
what is semicircular canals
loops of vestibular system
what is oval window
flexible membrane that transmits sound in ear
what is round window
another membrane
what is sensory epithelia
where afferent are for cochlea = perception of sound waves occurs, transduction and vestibular organs
what is utricle and saccule
vestibular organs
encodes horizontal and vertical acceleration of head
name vestibular organs
5 of them = 3 semicircular canals, utricle, saccule
describe flow of sound energy - beginning
tympanum = pushed by pressure waves
amplification modulated by skeletal muscles
linked to oval window by 3 bones = malleus, incus, stapes
what happens to tympanum when pressure
pressure decrease= eardrum pulled out
pressure increase=eardrum pushed in
describe amplification modulated by skeletal muscles
mechanical coupling of tiny bones innervated by skeletal muscles
contract when loud noise since limited range in which they can move = contract before sound to reduce amount of movement
if do not expect sound = will not contract and do job
large eardrum but small oval window = so force amplified, behind window = fluid
describe flow of sound energy - end
oval window = flexible membrane, pushed in or out, pressure waves go to flui
scala vestibuli = attached to oval window and pushes pressure waves down cochlea, fluid filled compartment
then comes back down
scala tympani
basilar membrane = vibrates up and down in response to pressure waves in compartments, mechanical properties of basilar membrane not uniform across cochlea
oval window pushes in = pushes out round window which moves back and forth
cochlear duct = scala media - in between 2 other scala
motion of basilar membrane is
Frequency dependent
locations of vibrations are a function of frequency of sound
describe where frequencies fall on basilar membrane
low frequencies = towards tip of cochlea
as frequencies increase = vibrations move closer to oval and round window
complex sounds = vibrations in multiple locations
what does basilar membrane encode
frequency of sound in location dependent manner
where is basilar membrane motion converted into neuronal activity
organ of corti
on top of basilar membrane = where afferent located
what does deflection of basilar membrane produce
shearing of hair cell stereocilia
describe organ of corti
4 rows of specialized hair cells down cochlea
hair on apical surfaces
describe inner hair cells
1 row
where afferents and transduction from
afferent synapse onto hair cells = release neurotransmitter and sends info to brain
describe what happens as basilar membrane moves to the stereocilia
stereocilia moves (activated to tectorial membrane)
bend or pulled in ways = move back and forth
describe outer hair cells
some afferents come from 3 outer rows of hair cells
but really receive afferents
describe outer hair cell electromotility
shorten when depolarized
lengthened when hyperpolarized
hair cell electromobility augments basilar membrane motion
alter how basilar membrane vibrates = allows cns to focus on certain properties by activating outer hair cells
describe clinical implications of outer hair cell electromotility
otoacoustic emissions = reflex, are used to evaluate hearing in newborns
outer hair cells make noise, do not hear them tho, makes click and can hear with microphone
way to test functioning = play click and wait for it to come back, if dont hear click = outer hair cells not doing what they should
hearing is important for language development
what do hair cells contain
mechanoreceptors
bend stereocilia
describe bending of stereocilia
Distance between ends of stereocilia are getting small as they are pushed or bent = clue as to where ion channels are
what connects stereocilia
tip links = tiny molecular threads attaching them
describe tip links
coated tip links between stereocilia
~15000 hair cells/inner hair cells in reach row = where transduction occurs
do not have many hair cells in cochlea
~10-20 stereocilia and one tip link per cell = ~100000 or 200000 tip links per cochlea
When break = problem
where are ion channels on cilia
on each side of tip link
as they move = tip link string pulls open channels when stereocilia move further apart
when move closer togetehr = tip links relax = less tension to ion channels close
what do tip links do
gate ion channels in stereocilia
each side ot tip link between taller and shorter stereocilia
pulls ion channel and lets potassium through = transduction
what does mechano transduction at tip link activate
afferent neurons
describe mechanotransduction at tip link
move in direction of tallest stereocilia = open
move in other direction = close
describe moving in direction of tallest stereocilia
k+ comes in and depolarizes cell and causes influx of calcium and neurotransmitter released on afferent and send ap to brain
why does potassium cause depolarization
fluid in cochlear duct is different from other fluids = it has high potassium, usually low potassium in ecf and high in cells but opposite in cochlear duct
what is tinnitus
ringing in ears
permanent
does not stop
name 2 types of tinnitus
transient
chronic
describe transient tinnitus
less and 24 hrs
usually due to loud noise
excessive mechanical stress of stereocilia
tip links are though to break but eventually grow back = ringing stops
describe chronic tinnitus
many causes but mostly loud noise
origin can be either inner ear, nerve or central pathways
Impacts quality of life - does not stop
mechanical damage or if damage to central auditory pathways
compare visual and auditory transduction - visual
photons = high energy but hard to catch, ~100x10^6 photoreceptors
trillions of opsin molecules
slow = g protein cascade
amplification closes many ion channels
compare visual and auditory transduction - auditory
sound waves = low energy but all around ~15000 hair cells, easy to catch but low energy
Several hundred thousand tip links
fast = direct channel activation
no amplification of transduction (yes mechanical but not of transduction)
describe cochlear implant
hair cell loss due to aging, loud sounds, ototoxic drugs
reestablish hearing in deaf
describe process of cochlear implant
implanted through round window
electrode place in scala tympani
Electrodes are spaced along the cochlear spiral to stimulate groups of afferent fibers that respond to different frequencies ~12 electrodes
sounds a bit diff but does work
what is deafness usually due to
transduction process does not work but afferents still there
so cochlear implants take sound through microphone and transmit through electrodes –> stimulates afferents and fire aps
decomposes frequency of sounds and stimulates right electrode in right location = figure out what frequencies are in sound= what basilar membrane does
describe central auditory pathways
8th cranial nerve - vestibular and auditory
enters brainstem at level of medulla
bilaterally represented across midline = ipsilateral and contralateral at same time
Thalamus
primary auditory cortex = recieves input from both ears
why is it important that receive info from both ears
use differences between sounds that being sent from each ear to do sound localization
name 3 steps to locating source
1 - time it takes sound to enter and activate cochlea on both sides (sound on left hits right cochlea later, microseconds but neurons are sensitive to it)
2 - head blocks pressure waves so amplitude depends on how its coming towards you
3 - pinna (ear) reflects sound coming in diff directions and also helps determine ability to locate sound
neurons use slight differences to help determine where sound is coming from
