Auditory III

Question 1

Anatomic path for auditory

Answer 1

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

Question 2

ANF bifurcates into

Answer 2

• one branch innerv ventral cochlear nucleus

- one branch innerv dorsal cochlear nucleus

Question 3

axons from DCN and VCN enter lateral lemniscus as

Answer 3

dorsal acoustic stria (from DCN) or trapezoid body (from VCN)

Question 4

other axons besides DCN and VCN in lateral lemniscus

Answer 4

axons from:
superior olivary complex and nuclei of lateral lemniscus

medial olivocochlear neurons (MOC) of superior olivary complex feed back to OHCs

Question 5

inferior colliculi receive projections from

function?

Answer 5

cochlear nuclei and multisynaptic input from pontine nuclei of superior olivary nucelus

obligatory relay and integration center for ascending auditory info

Question 6

what happens to fibers from inferior colliculus

Answer 6

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

Question 7

fibers in MGN staying on same side are linked by ___

compared to fibers that join on opposite side

Answer 7

same = assoc fibers

opposite = anterior commissure

Question 8

___ contains the cochleo-topic (tonotopic) map

Answer 8

cortical surface

Question 9

Interaural time difference vs intraural time diff

Answer 9

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

Question 10

Ex of interaural time diff

sound on R side
sound in front
max ITD?

Answer 10

freq

Question 11

Ex of intraural time diff

used for what type of sounds

Answer 11

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

Question 12

define monoaural spectral shape

Answer 12

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

Question 13

A1 includes

A2 includes

Answer 13

A1 = tonotopic map
A2 = Wernicke's area = understand and process spoken language

Question 14

how is auditory cortex arranged

Answer 14

arranged in tonotopic map

Question 15

spectral cues

Answer 15

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

Question 16

duplex theory of sound localizations

Answer 16

low freq = ITDs

high freq = ILDs

Question 17

inferior collicules receives direct projections from ___

and multisynaptic input from

function of inferior colliculus

Answer 17

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

Question 18

what happens after fibers reach MGN

Answer 18

MGN sends to primary auditory cortex via auditory radiations

Question 19

is the auditory cortex connected across hemispheres?

Answer 19

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

Question 20

Distinguish btwn type 1 and type 2 fibers of CN 8

Answer 20

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)

Question 21

where do axons decussate in auditory pathway?

Answer 21

superior olive and trapezoid body fibers

Question 22

what happens if you have unilat lesion rostral to cochlear nuclei

Answer 22

no unilat deafness because axons from cochlear nucleus join ipsil lateral lemniscus while others join contralat lat lemniscus

Question 23

what happens if you have unilat lesion caudal to cochlear nuclei and including CN

Answer 23

unilateral deafness

also deficit in sound source localization if just CN

Question 24

Distinuish btwn ITD
ILD
Specctral

Answer 24

ITD = freq less than 1.5 khz

ILD = freq greater than 1.5 khz

Spectural = freq greater than 5 khz

Question 25

Describe ILD
what freq detect

why

Answer 25

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

Question 26

Describe ITD

why

max ITD for humans?

Answer 26

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

Question 27

when is diff in intensity used by auditory system to localize sounds

what type of freq is detected

what structure is being used

Answer 27

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)

Question 28

when is time of arrival used

what type of freq is detected

what structure is being used

Answer 28

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