audition Flashcards
what is sound?
periodic, sinusoidal changes in air pressure
compression vs. rarefaction?
compression
- made more dense, peaks
rarefaction
- made less dense, troughs
what is pitch determined by?
frequency
- low freq - low pitch
what is intensity determined by?
amplitude
- low amp - low intensity
what is a threshold and how to they change?
different animals have different thresholds for frequency and intensity
they have an audible and inaudible range of frequencies
big-pinnaed animals
evolutionarily they prioritize
focussing sound into the auditory canal -> collecting sound energy
parts of outer ear?
answer and define
PA
pinna
auditory canal
parts of middle ear?
TOE OW
tympanic membrane - ear drum
ossicles
eustachian tube
oval window
parts of inner ear?
C RW
cochlea, coiled structure connected to the auditory vestibular nerve
round window
what parts of the ear are air filled vs. fluid filled?
outer ear = air-filled
middle ear = air-filled
inner ear = fluid-filled
outer ear: pinna
the fold and bumps on surface of ear
- made of cartilage
- funnels sound waves down the auditory canal
- important for vertical sound localization
outer ear: auditory canal
- what does it contain, what does it do?
- filled with air
- collects sound, entrance to the middle and inner ear
middle ear: tympanic membrane
sound waves move/vibrate the tympanic membrane
- vibrates at the same frequency the sound has when it entered the ear
middle ear: what are ossicles?
bones in the middle ear
what are the different bones in the ossicles?
MIS-OW
malleus - hammer
incus - anvil
stapes - stirrup
what does the stapes do?
acts as a piston that moves in and out of the oval window
middle ear: eustachian tube
keeps air in the middle ear continuous with air in the nasal cavities
- has a valve thats usually closed
- if pressure changes, yawning/swallowing opens valve and equalizes pressure
what is impedance matching, why is it important?
what:
large amplitude low energy sound waves are transformed into
–> small amplitude, large energy sound waves
why:
impedance of air is low, impedance of fluid is high - meaning air is easier to move than fluid
mechanisms must be in place to allow for the fluid to move
how do we amplify sound waves in impedance matching?
the ossicles!
1) increase force through lever action
- ossicles turn large movements at eardrum to smaller but stronger movements at stapes
(incus and malleus)
2) surface area of the stapes at the oval window is smaller than that of the tympanic membrane
- meaning force is concentrated in a smaller area
what is the attenuation reflex?
reflex gets triggered by the onset of loud noises
- adapts the ear to continuous loud noise, protects delicate ear machinery
when does the attenuation reflex activate?
- it has a delay
- when we speak
- continuous loud noises
how does the attenuation reflex work mechanically?
- what muscles are involved?
tensor tympani - malleus
stapedius - stapes
1) when these muscles contract, the ossicles become more stiff
2) reduces sound conduction to the cochlea
aka. sound conduction from air to the fluid in ear
inner ear: cochlea?
fluid filled chamber
- cochlea sends signals to brain through the auditory vestibular nerve
stapes presses on membrane of the oval window
- fluid is displaced -> neuronal response
- sound frequency gets transduced into electrical signals
what are the fluid filled compartments cochlea?
made of 3 fluid filled compartments
- scala vestibuli (oval window)
- scala media
- scala tympani (round window)
what is the reissners membrane?
membrane that separates scala vestibuli and scala media
basilar membrane?
separates scala media and scala tympani
what movement occurs in the basilar membrane?
it is displaces when the stapes moves
what are the components near the basilar membrane?
organ corti
tectoral membrane
tectorial membrane?
hangs over the organ of corti
organ of corti?
sits on top of the basilar membrane, contains auditory receptor neurons(hair cells)
what are the hair cells, where are they located?
- auditory receptor neurons
- located in the organ of corti
what happens when all the membranes stay rigid and the ossicles are vibrated?
1) oval window moves
2) fluid in scala vestibuli moves
3) goes though helicotrema
4) fluid in scala tympani moves
5) fluid pushes out the round window
what are the fluids in the cochlea?
where are they located?
what are the ionic concentrations that are present?
perilymph
- in scala vestibuli and tympani
- low K+, hi Na
endolymph
- in scala media
- hi K+, low Na
what is the endocochlear potential?
how does it compare to that of the perilymph?
+80mV
it is 80mV more positive than perilymph
how are the concentrations maintained?
what does the — do?
by the stria vascularis
- absorbs Na+ from and secretes K+ into endolymph
what does the movement of the stapes cause?
causes the oval window to move
which causes a wave to travel down the basilar membrane
what is the structure of the basilar membrane?
describe those structures
- narrow, stiff base (closer)
- wide and, floppy apex (further)
how do high and low frequency sounds effect the basilar membrane?
high = vibrate base
- can move more easily to the stiff base
low = vibrate apex
what is important about the organ of corti?
they contain hair cells
2 key components of hair cells?
1) each hair cell has at least 10-300 stereocilia, look like hairs
2) hair cells are NOT neurons, they are specialized epithelial cells
how does sound energy affect the stereocilia?
sound energy bends the sterocilia, producing a neuronal signal
where are hair cells located?
located above the basilar membrane and extend above the reticular lamina
inner hair cells
- location, amount and rows
- between modiolous and rods of Corti
- 4k per cochlea, 1 row
outer hair cells
- location, amount and rows
- further out from rods of Corti
- 12k per cochlea, 3 rows
where do hair cells synapse onto?
spiral ganglion cells
what are spiral ganglion cells?
bipolar neurons that get input from hair cells and extend to the CNS
somas are located in the spiral ganglion modiolus
where do the spiral ganglion axons reach?
auditory nerve -> cochlear nuclei
inner vs. outer hair cells and spiral ganglion cell synapses?
inner
- synapses with many spiral ganglion cells
- responsible for 90% of SGC input
outer
- synapses with 1 spiral ganglion
- responsible for 10% of SGC input
what are outer hair cells most involved in?
cochlear amplification
what are inner hair cells most involved in?
auditory transduction
tip location of OHC vs. IHC?
IHC = above reticular lamina into endolymph
OHC = extend above reticular lamina but end in tectorial membrane
how do outer vs. inner hair cells bend?
OHS - pushing of tectorial membrane
IHS - displaced endolymph
BM up vs. down? (hair)
up = stereocilia bend away from modiolus (left)
down = stereocilia bend towards modiolus (right)
what do hair cells release, and where?
excitatory transmitter onto 8th nerve auditory axons via synapses
what are stereocilia made of?
are rigid bundles of protein, mostly actin
what are located on the tips of stereocilia?
Tip link K+ channels
how do the stereocilia move as 1 unit?
cross-link filaments
how are the Tip link K+ channels gated?
They are mechanically gated
Describe Tip link K+ channels under the following conditions
- up
- towards kinocilium
- away from kinocilium
up = half open half closed
towards kinocilium/right = open more(more depolarization)
hair cell left
way from kinocilium/left = hyper-polarization (no depolarization)
hair cell right
what causes depolarization?
- endochoclear potential = 80mV, which is higher than inside the cell
- K is high in and out but the charge gradient pushes K+ into the cell
(because of the high driving force, small bends cause large Vm changes)
when is the response to bending saturated?
when you displace basilar membrane 20nm or more away
what are the two properties of endolymph?
1) High K+ in endolymph
- no gradient of K+ across the hair cell membrane
2) Large endocochlear potential
- drives K+ from outside(endolymph) to inside (hair cells) creating a current and a receptor potential
what are the most important factors of real-world sounds such as speech interpretation?
frequency and TIMING
how is frequency represented in the nervous system?
1) Tonotopy
- each auditory nerve fiber is sensitive to a narrow range of frequencies
2) Timing
- auditory nerve fibers fire action potentials in synchrony with sound waves works for lower frequencies
how does tonotopy work?
cochlea is a spectral frequency analyzer, and auditory axons are arranged in a tonotopic pattern
timing
1) the timing of action potentials provides a second neural code for acoustic frequencies
2) the timing of spikes via a second neural code for acoustic frequency
Paradox #1: what does the ear act as?
The ear is both a detector and emitter
what is otoacoustic emission?
what are the 2 types?
define them
sounds generated by the ear
evoked
- triggered by a short click and recorded just outside the ear
- used to test infant hearing
- normal
spontaneous
- no stimulus needed
- happens to 50% of people, associated with damage in the ear
Paradox #2: what are the rows of OHC vs. IHS? what are their specializations?
1 row of inner
3 rows of outer
IHS
- brain receives most input from
OHS
- can contract and expand using motor proteins like prestin
- by changing length, they amplify the amount of the basilar membrane that vibrates
- its a positive feedback loop
what does prestin do for OHC?
prestin changes OHC length in response to changes in the oHC membrane potential
what happens when OHC change length?
they amplify the amount of the basilar membrane that is vibrated/displaced
what would happen if one did not have OHC?
- they would loose the ability to hear weak/low-intensity sounds
- positive feedback loop
what does furosemide affect?
inactivates OHC motor proteins, therefore reducing basilar membrane movement in response to sound
reduces transduction from stereocilia bending
so how to OHC respond to sound?
they are a cochlear amplifier
- respond to sounds by changing length
- pushing and pulling on the basilar membrane
- basilar membrane movements would be only 1% as large without this amplifier
where do the right and left ventral cochlear nuclei project?
- To both R & L superior olives
- All ascending pathways converge at the inferior colliculus
where do the ascending pathways converge?
at the inferior colliculus
what lobe of the brain is responsible for auditory?
what cortex?
- the temporal lobe
- Auditory cortex/A1 (Area 1)
how does the medial geniculate project through the A1?
Acoustic radiation, through internal capsule
What are isofrequency bands?
neurons organized in columns of cells according to frequency
- similar orientation columns in V1
what happens if you lesion 1 side of the A1 cortex?
it does not cause unilateral deafness, because both A1 cortices get input from both ears
what is the wenickles area?
area involved with language processing, speech comprehension
what are the two ways that the intensity of a sound are encoded?
1) more vibration in basilar membrane -> more movement of stereocilia
-> more hyper or depolarization
-> auditory nerve neurons fire more frequently
2) more displacement of the basilar membrane
-> more hair cells activated
-> more action potentials fired by auditory nerve
what are the 2 ways that frequency are encoded?
1) tonotopy
-> each nerve neuron is sensitive to a narrow range of frequencies
2) timing
-> auditory nerve neurons synchronize
their firing of APs with sound waves
-> used for lower frequencies
expand on tonotopy encoding frequency?
-> basilar membrane
-> place code
- basilar membrane is organized tonotopically
- different frequencies maximally stimulate specific regions of the BM
place code
what happens when the basilar membrane moves - in the context of frequncy
- associated hair cells move too
- IHCs synapse with 1 spiral ganglion neuron
- so specific neurons will be activated the most by specific frequencies
- these neurons respond to a narrow range of frequencies matching their IHC frequencies
tonotopy in the cochlear nucleus?
- high frequency = posterior
- low frequency = anterior
how is A1 tonotopically arranged?
isofrequency bands
- hi freq = posterior and medial
- low freq = anterior and lateral
what does tonotopy work best for?
what is the cutoff
high frequency sounds
- tonotopic maps dont contain neurons that have frequencies lower than 200Hz (meaning those frequencies would sound the same)
how are low frequency sounds heard?
phase locking
what is phase locking associated with?
what is phase locking?
associated with
- encoding frequency
what is it?
- neurons synchronize their firing with sound waves, so they fire at the same phase as the sound wave
what is the volley principle?
if we take a group of phase locked neurons we can make up for the fact that they might not fire every cycle
- some neurons will fire when others don’t so with a good enough group, we will have at least 1 neuron firing cycle
- helpful for intermediate frequencies that might be a little too fast for neurons to fire every cycle
how do we locate the azimuth of a sound source?
1) interneural time delay
2) interneural intensity difference
3) ongoing sounds = move head
interneural time delay
- frequency
- mechanism
frequency
- 10-2k
mechanism
- sound wave peak reaches each ear at different times
- 10-30 microsecond differences
interneural intensity difference?
- frequency and mechanism
frequency
- 2k-20k
mechanism
- head creates a sound shadow that dampens the intensity of a sound at the other ear
how do you locate the elevation of a sound?
- it depends on reflections off surfaces of the pinnae, and summation of the sounds entering the auditory canal directly and after reflection
what frequency is the pinna focussed on most?
it is best at letting high frequency sounds into the auditory canal
high and low frequencies
encoding vs. localization
encoding
- high = above 5Hz
- low = below 200 Hz
localization
- high = 2k-20kHz
- low = 20-2,000Hz
what causes most deafness or hearing impairments?
what could go wrong, why is it so permanent
- defects in cochlear, damage to hair cells
- there are a lot of proteins associated with the function of the cochlea
- hair cell damage due to
-> loud sounds, ototoxic drugs, infection, autoimmune disease, aging and genetics
permanent because hair cells do not regenerate!
how can damage be treated? (2 ways)
- hearing aids: pick up and amplify sound
- cochlear implants
-> takes sound wave frequencies and stimulates the respective spiral ganglion cells directly
-> stimulation patterns electrically trigger action potentials in the auditory nerve axons
-> bypasses the hair cells and exploits the tonotopy of the cochlea
language and cochlear implants?
modern cochlear implants allow the typical patient to understand more than 90% of the words in unfamiliar sentences when presented in quiet listening conditions
influence of age?
a critical period that expires within the first 3 years with best performance occurring with implantations in the first 12-18 months
