AVS Reflexes and Evoked Potentials Flashcards
Is evoked spontaneous?
no, it needs something to stimulate it to get a response
what are potentials?
measure voltage changes that we evoked by a sound
ex: receptor, resting membrane, action potentials
How do we test our acoustic reflexes?
ART and reflex decay
what frequencies do we test for ART
500 Hz, 1000 Hz, 2000 Hz, 4000 Hz
What frequencies do we test for reflex decays
500 Hz, 1000 Hz
what is the normal range for testing ARTs?
70-90 dB above pure tone AC threshold
what are the reflexes for the vestibular system?
Vestibulo-ocular (eyes)
Vestibulocollic (neck)
Vestibulospinal (spinal cord)
negative polarity at one end and a positive polarity at the other end
dipole
Needle electrodes during a surgery
near field
disc/surface electrodes in a clinical office
far field
What are the cochlear microphonic?
alternating current potential that follows the waveform of the evoking stimulus
mimics the stimulus and AC looks like a sine wave
generated by the outer hair cells mainly (some contribution from IHC)
What is summation potential
direct current produced in the cochlea in response to a sound
derived mainly from IHC but some OHC as well
ABR wave I?
distal CN VIII (cochlea area of spiral ganglia)
ABR wave II?
proximal CN VIII (Closer to BM) (approaching brainstem)
ABR wave III?
cochlear nucleus
ABR wave IV?
SOC
ABR wave V?
LL / IC
What does an ABR do?
measures absoute latency (where did it occur)
interpeak latency
amplitudes
amplitude ratio
what is the largest and most stable wave of an ABR?
Wave V - IC and LL
normal time at peak one of ABR
1.5 msec
normal time between waves 1 and 5 in ABR
5.5 msec
normal time at peak III of ABR
3.5 msec
normal time at peak II of ABR
2.5 msec
normal time at peak IV of ABR
4.5 msec
normal time at peak V of ABR
5.5 msec
what is the overall interpeak latency of waves I-V of ABR
4 msec
What does wave I also represent?
compound action potential of ECochG
What if the Wave I-III latency was normal and only the Wave III-V interpeak latency showed abnormalities?
would indicate a lesion in the CANS was higher than the cochlear nucleus region and can guide further testing and imaging
what would we see if there is damage to the cochlear nucleus? Would we see a reflex arc?
pure tone hearing loss on the ispi side to damage. no reflex on ispi or contra
why is important to have a variety of cells in the CN and responses from those cells?
auditory life would be boring if we only had octopus giving us onset responses (would
world wouldn’t work well with communication or music if all we had was an onset responses and no other information and all we know is when it starts and that is it
variety of cells for responses to have rich auditory environment captured that we live in
think about only seeing one color
What are response patterns in the CN?
rimary-like: initial spike and then steady response
Chopper-on-off and on-off
Onset-One initial spike and nothing else
Pauser-similar to primary with a pause
Build up—gradual increase
excitatory neurotransmitters in CN
glutamate and aspartate
inhibitory neurotransmitters in CN
GABA and glycine
descending neurotransmitter in CN
Acetylcholine and noradrenaline
what is the largest projection from the CN?
trapezoid body tract coming from AVCN
Where are EE cells and what do they respond to
MSO and respond to phase differences (ITD)
Where are EI cells and what do they respond to
LSO and respond to intensity differences (ILD)
EE = excited by both ____
Contralateral & ipsilateral input
EI =
excited contralateral and inhibited ipsilaterally
IE =
excited Ipsilateral and inhibited contralateral
if both ispi and contra are inhibited
II cell
first letter describes
contralateral response (E or I)
second letter describes
neurons response to sound in the ipsi ear
why are pure tones not affected at the SOC?
they are already at the point of redundancy and enough gets through for a basic detection of the sound
clinical significance in SOC
Pure tone thresholds not likely to be affected
Localization can be affected
Wave IV of ABR (some contribution to V)
Contralateral acoustic reflex abnormalities, ipsilateral reflexes may be present
Poorer performance on tests which rely on binuaral integration (Masking Level Difference and others)
What is the cell type of LL
mainly multipolar globular cells with elongated neurons
tonotopic organization of LL
lows dorsal highs ventral
what part of LL is important for startle reflex?
VNLL
where is the obligatory relay station of the ascending auditory pathway
inferior colliculus
what relies on IC?
dichotic listening tasks and localization and orientation of the head
what is sensitive to binaural stimuli and interaural differences
MGB and IC
what is the hypothesis of the MGB
it begins the processing of speech
tracts that run from the spinal cord and through the BS to cerebrum with many nuclei
RF
what systems are conneCted to RF
auditory, sensory, motor
what are the two divisions of RF
ascending reticular activation system and motor activation system
what is our alarm or alerting system
ARAS of RF
mechanism that helps with selective attention and listening in noise
ARAS of RF
what is the main pathway from the MGB to the cerebrum
thalamocortical projections to cerebrum
why is redundancy important
speech and communication in our rich environment
have multiple ways for sound to get from cn 8 to cortex
starts after leaving cn
goes ipsi, contra and through commisures to the cortex
what is the primary auditory area
heschl’s gyrus
is A1 planum temporale and the lateral fissure the same on both hemispheres?
no, larger on the left hemisphere where it is speech dominant
receptive language processing area and spatial hearing area
planum temporale
what is spatial hearing
in room with different noises and can close eyes and can tell where things are (ac or car going by)
can visual or spatial map in mind by what you hear
blind people
hear in noise
helps us maneuvar in the wosrld
speech reception
wernickes
expressive/motor
broca’s
associate words with images, sensations amnd ideas
angular gyrus
what gyri integrate auditory somatic and visual info
wernickes brocas supramarginal and angular gyrus
responsible for temporal sequencing of acoustic events
insula
gray matter that is medial to the insula and sensitive to auditory info
claustram
