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67 Cards in this Set

  • Front
  • Back
definition of sound
sinusoidal oscillations(waves) of air compressions and rarefractions in an elastic medium
Human freqency hearing range
20Hz-->20KHz
how is loudness measured


for every 10fold inc in amplitude
on a log scale in Decibels(Db)


we perceive an equal increment in sound
Loudness=

Pref
20 X log(10) P/Pref

threshold of sound detection at best frequency
humans=1 KHz
damage occurs at
120dB
damage to cochlear nucleus leads to

nucleus is not bilaterally innervated, BUT...
ipsilateral hearing loss


after it leaves, it crosses giving bilateral innervation
outer ear

middle ear

inner ear
collects sound

transmission/amplification from ear->cochlea via:incus, malleus, and stapes

processes auditory information
-converts mech E to elect E
in the cochlea
Basilar membrane
separates scala media and scala tympani, continuous
Base
near oval window
narrow in width
responds to high freq
Apex
respons to lower freq
looser and resonates better
the narrow base to wide apex is the basis for?

dfft sections of the basilar membrane
Primary Basis for encoding frequencies

respond to dfft frequencies
Place Encoding
freq is encoded by the position of transduction along the basilar membrane
Scala Media
contains endolymph- high in K
continuously replinished by Stria Vascularis
Stria vascularis
maintains endolyph in scala media by simply replacing it, not active transport
Scala Tympani and Scala vestibuli
have Perilymph
approx conc to regular CSF, low K conc
tectorial membrane is on top of what?
the organ of corti
Hair cells
the principle transducing apparatus
1. Outer hair cells
2. inner haircells
Inner Hair Cells
3500 total
more important in hearing
-loss is significant
respond to primary freq of basilar memb vibration
-base=high, apex=low
Outer Hair Cells
14000
loss of these leads to strange alterations in sensitivity
what do outer hair cells modulate?
modulate afferent signal back to the CNS by changing the mechanical properties of basilar membrane
the main afferent sensory nerve


cell bodies are located where?
1. runs to spiral ganglion
2. out to cochlear nerve

in the spiral ganglion
Hair cell has
apical surface
basilar suface
endolymph at apical
perilymph at basilar
high conc of K affects what

apical
basilar
depolarizes the apical memb of cell
normally neg potential
normally depolarized by K
Activation of hair cell
1. k flows across apical surface
2. voltage dep Ca chann act
3. voltage dep Ca chann also activate Ca sensitive K chan
4. K chan allow k to be pumped across basal surface, out of cell
-k transport across entire cell
Bundles of cilia

main cilia on top is called
on apical surface of hair cell
initiate K transport on apical
Kinocilium
Linkers
between the cilia are proteinaceous briges

*attached to mechanically operated ion channels
mechanical work moves linkers, leads to what?
1. opening Ion channels and K flows in
2. depolarizes cilia
3. travels down to apical memb
4. depolarizes apical and initiates signal trasduction
OHC are attached to what?

what does this mean?
tectorial membrane

when tect membrane moves there is a mechanical sharing of energy and this pulls cilia channels open
encoding via
different hair cells are more sensitive to different frequencies

tuning freq depends on where its located on basilar membrane
most hearing loss is due to?
hair cell damage
cochlear implants are successful because
place encoding for frequency
how do you replace a loss of all IHC?
direct stimulation of the afferent nerve by a coiled wire that runs under basilar membrane

only 8 key freq needed for hearing
synapsing
presynaptic membrane has a lot of vessicles

same Ca dependent trandsuction mechanism
what is the primary afferent transmitter?
Glutamate
what is the ratio for afferent signaling in OHC
10:1 eff:aff
a lot less afferent signaling

NOT part of transmission to auditory system
SON sends...
efferent fibers to OHCs and IHCs
each inner hair cell has
1:10 eff:aff
a lot more afferent signals, heavily afferent
afferent IHC signaling encodes for
1. freq
2. loudness
3. location
4. bilateral inputs
what is the main role of OHC?
central regulation is the main function
they are attached to basilar membrane, reamplify signal
recover mech E lost by dampening of the media
Antimasking suggests that


stimulating what hair cells?
efferents from CNS do play a role

OHC picks out signals from background noise
when OHC are inactive
flat higher firing rate of IHC at lower frequencies

not detecting tone bursts to level of 50dB
when OHC are active
1. lower firing rate at low freq
2. get antimasking of noise
3. allow detection of tone burst at lower sound intensities
4. allows IHC to have a wider dynamic range
Overall:
IHC are

OHC are
primary transducers of sound

regulate the behavior of IHC and sensitivity
loudness saturates at
500 spikes/sec
Phase Locking
in the oscilations of a sine wave, we only see things at the peak or trough

peak-opens K chan
tough- closes K chan
number of APs in the peak rep

space b/w APs represents
loudness

frequency
Localizing Sound

auditory info enters thru
cochlear nucles, then sends to dfft places, dividing up the qualities: loudness, location,etc
at the level of the SON, sound travels to the...
Trapezoid Body
this results in bilat info processing
travels through Lateral Lemniscus to..

then to..
Inferior Colliculus (wine glass)


medial geniculate of thalmus
and finally to auditory cortex
sound is localized when
it reaches one cochlea before the other
the sound from the opp ear of sound will determine
what cells the sound will feed into and when it will feed into them
big delay in sound

shorter delay
will detect coincidence at more distal cells
will detect coincidence at more proximal cells
location of a cell where coincidence is detected allows you to tell?
how far a sound is displaced from the midline
Intensity difference is detected

cell responds best when
by Lateral SON

intensity from ipsilateral side exceeds the other
Inferior colliculus is the first place that...
takes information from BOTH SON and puts it int a map

maps where sounds are

directs attention to sound
Medial Geniculate nucleus
auditory nucles in thalmus
Transverse Temporal Gyrus
Heschel's Gyrus
on top of temporal lobe

Primary auditory cortex
Tonotopy, how are they organized?

cells look at dfft...
based in terms of their freq coding

1. freq 2. location 3. loudness
Heschel's Gyrus is near
Wernicke's gyrus-language processing

sends info to Broca's area
where is sound localized?
inferior colliculus
medial SON
at low frequencies what dominates?

at high frequencies what dominates?
phase locking: only have APs at peaks

freq generate APs at specific locations in the basilar membrane
medial SON

lateral SON
processes location of sound

processes intensity of sound
if there is a BIG delay in sound, the coincidence of input is more?
distal
if there is a SMALL delay in sound, the coincidence of input is more?
Proximal
The Inferior Colliculus (IC) receives
both medial and lateral SON

integrates both localization and intensity
Transvers Temporal Gyri=
Heschel's gyrus
Heschel's gyrus demonstrates...


cells look at..
Tonotopy- based on freq coding


1. freq 2. location 3. loudness