Auditory III Flashcards
Anatomic path for auditory
1) ANF with cell body in spiral ganglion send signal to cochlear hair cells of brain (axons form auditory part of CN 8)
2) enter brainstem, bifurcate
- one branch innerv ventral cochlear nucleus
- one branch innerv dorsal cochlear nucleus
(nuclei on dorsal and lateral inf cerebellar peduncle)
3) some axon cross midline via dorsal acoustic stria (from DCN) or trapezoid body (from VCN)
4) regroup as lateral lemniscus and ascend to inferior colliculus (mdibrain)
______
5) some axon terminate in pons (superior olivary complex and nuclei of lateral lemniscus)
6) medial olivocochlear neurons (MOC) of superior olivary complex feed back to OHCs
7) both #5 and #6 join lateral lemniscus ipsil to inferiro colliculus
8) other axons join lateral lemniscus ipsil and terminate in inferior colliculus
ANF bifurcates into
- one branch innerv ventral cochlear nucleus
- one branch innerv dorsal cochlear nucleus
axons from DCN and VCN enter lateral lemniscus as
dorsal acoustic stria (from DCN) or trapezoid body (from VCN)
other axons besides DCN and VCN in lateral lemniscus
axons from:
superior olivary complex and nuclei of lateral lemniscus
medial olivocochlear neurons (MOC) of superior olivary complex feed back to OHCs
inferior colliculi receive projections from
function?
cochlear nuclei and multisynaptic input from pontine nuclei of superior olivary nucelus
obligatory relay and integration center for ascending auditory info
what happens to fibers from inferior colliculus
1) project to ipsil MGN of thal or contralateral inferior colliculus and contralat MGN
2) MGN send to primary auditory corte (A1) of superior temporal gyrus via auditory radiations
3) same side = fibers linked by assoc fibers
opp side = linked by anterior commissure
fibers in MGN staying on same side are linked by ___
compared to fibers that join on opposite side
same = assoc fibers
opposite = anterior commissure
___ contains the cochleo-topic (tonotopic) map
cortical surface
Interaural time difference vs intraural time diff
interaural = sound reaches from source to each ear differently due to physical separation by head in space –> direction depednent differences in path lengths
intraural level differences = head causes level differences that cue to sound location –> direction depedent diff in amplitudes
Ex of interaural time diff
sound on R side
sound in front
max ITD?
freq
Ex of intraural time diff
used for what type of sounds
high pitch sound > 1.5 kHz
sound hits closer ear and becomes attenuated when reach further ear –> direction depedent diff in amplitudes
high freq sound —> wavelength of sound shorter than size of head so sound reflected off near side of head —> acoustic shadow so sound
intensity at ear furthest from source is less than near source
define monoaural spectral shape
change systemically with source elevation
arise from direction and freq depednent reflection and diffraction of pressure waveforms of sound by pinna that change with location
A1 includes
A2 includes
A1 = tonotopic map A2 = Wernicke's area = understand and process spoken language
how is auditory cortex arranged
arranged in tonotopic map
spectral cues
generated by way sound interact with pinna
learn to use differences in tamber (quality of sound)
amplifies sound forward and identical sound different if behind us
duplex theory of sound localizations
low freq = ITDs
high freq = ILDs
inferior collicules receives direct projections from ___
and multisynaptic input from
function of inferior colliculus
cochlear nuclei
nuclei of superior olivary complex
relay and integration for ascending auditory info and project to ipsil MGN thalamus and contralat inferior collic and MGN
what happens after fibers reach MGN
MGN sends to primary auditory cortex via auditory radiations
is the auditory cortex connected across hemispheres?
yes linked by assoc fibers on same side and via anterior commissure for regions on opposite side
good preservation of tonotopic organization of cochlea throughout
Distinguish btwn type 1 and type 2 fibers of CN 8
type 1 = 90-95% myelin = synapse with innerhair cell (1 to 1)
type 2 = 5%, unmyelin = synapse with outer hair cell (many more OHC than type 2)
where do axons decussate in auditory pathway?
superior olive and trapezoid body fibers
what happens if you have unilat lesion rostral to cochlear nuclei
no unilat deafness because axons from cochlear nucleus join ipsil lateral lemniscus while others join contralat lat lemniscus
what happens if you have unilat lesion caudal to cochlear nuclei and including CN
unilateral deafness
also deficit in sound source localization if just CN
Distinuish btwn ITD
ILD
Specctral
ITD = freq less than 1.5 khz
ILD = freq greater than 1.5 khz
Spectural = freq greater than 5 khz
Describe ILD
what freq detect
why
high freq sounds (small wavelength)
head creates acoustic shadow for far ear as sounds with wavelength equal or less than head diameter reflected off
therefore, sound at ear further from source attenuated compared to near ear = amplitude difference
Describe ITD
why
max ITD for humans?
low freq sounds
ears separated in space by head
different times of arrival to each ears so a sound on right will reach right ear short time before left
max ITD = 800 us
when is diff in intensity used by auditory system to localize sounds
what type of freq is detected
what structure is being used
high freq = ILD
medial nucleus of trigeminal body + LSO are biased to neurons sensitive to high freq unlike MSO
LSO neurons compute difference in intensities due to ipsil excitation and contralat inhib via rate code (# of AP proportion to intensity of sound)
when is time of arrival used
what type of freq is detected
what structure is being used
low freq = ITD
physical time delay to ears causes AP to reach MSO at slight diff times
at some point AP meet together at MSO to determine location
