Auditory system- lecture 17 and 18

Question 1

Which auditory field is concerned with sound localisation?

Answer 1

The posterior auditory field

Question 2

The outer ear helps with sound localisation in which plane?

Answer 2

The vertical plane

Question 3

What is the other word for horizontal plane?

Answer 3

Azimuth

Question 4

Is sound localisation in the horizontal plane represented on the basilar membrane?

Answer 4

No

Question 5

What does localisation in the horizontal plane require?

Answer 5

2 ears- interaural disparities in timing and intensity

Question 6

Why is the pre-cortical pathway so intricate in the auditory pathway?

Answer 6

It functions to bring information from both ears together

Question 7

What are the two interaural cues devised by Rayleigh 1907 for sound lcoalisation?

Answer 7

1. Interaural time difference
2. Interaural level difference

Question 8

What are the two components of interaural time differences?

Answer 8

onset time of the sound and phase differences

Question 9

What is the path difference?

Answer 9

The slightly longer distance a sound travels to reach one each compared to the other

Question 10

What is the maximum interaural time difference?

Answer 10

0.65 msec which occurs when a sound is directly into one ear (90 degrees from directly ahead)

Question 11

What is the only interaural cue available for very short sounds like clicks?

Answer 11

Time onset

Question 12

What determines the phase difference?

Answer 12

The path difference

Question 13

At what frequency sounds is phase difference useful to us?

Answer 13

Low frequency sounds

Question 14

Describe why low frequency sounds can use phase difference

Answer 14

If 1/2 the waveform exceeds the diameter of the head then the low frequency sound will enter each ear at different phases

Question 15

Why cant higher frequency sounds use phase differences?

Answer 15

When the wavelength is equal to or less than the diameter of the head, the sound can enter both ears at the same phase even if there is a path difference.

Question 16

Up to what frequency can we use phase differences?

Answer 16

1500Hz

Question 17

What is the optimal frequency for phase locking?

Answer 17

750Hz

Question 18

At what frequencies does the head cast a shadow?

Answer 18

At high frequencies

Question 19

What does the sound shadow cause?

Answer 19

Changes in interaural level differences.

Question 20

Why don’t low frequency sounds cast a sound shadow?

Answer 20

the waveform bends

Question 21

Do low frequency sounds show interaural level differences?

Answer 21

No

Question 22

What are the 4 nuclei of the superior olivary complex?

Answer 22

Medial SO, Lateral SO, Medial nucleus of the trapezoid body, lateral nucleus of the trapezoid body.
MSO, LSO, MnTB, LnTB

Question 23

What are the trapezoid body fibres?

Answer 23

Connect the cochlear nucleus to the SOC

Question 24

Which distinct cells in the cochlear nucleus send outputs to the SOC?

Answer 24

Spherical and globular bushy cells

Question 25

Which nuclei in the SOC is concerned with interaural time difference?

Answer 25

MSO

Question 26

Which cell type in the CN sends direct connections to the MSO from the left and the right?

Answer 26

Spherical bushy cells

Question 27

Where do the globular bushy cells send connections to?

Answer 27

The MnTB (on opposite side) and LnTB (on same side)

Question 28

Connections going to the same side SOC will go to which nucleus?

Answer 28

The LnTB

Question 29

What type of connection is it from the MnTB and LnTB to the MSO?

Answer 29

Inhibitory- glycinergic

Question 30

Describe the connections to the MSO

Answer 30

It receives excitatory connections from spherical bushy cells from the ipsi and contralateral sides. It receives inhibitory connections from the LnTB which comes from globular bushy cells on the same side, and inhibitory connections from the MnTB which gets inputs from globular bushy cells on the opposite side

Question 31

What nuclei in the SOC is concerned with interaural level differences?

Answer 31

The LSO

Question 32

Describe the inputs to the LSO

Answer 32

excitatory input from spherical bushy cells on the same side, and inhibitory inputs from globular bushy cells on the opposite side via the MnTB

Question 33

Where are comparisons made about ILD from inhibition from one ear and excitation from other ear?

Answer 33

LSO

Question 34

How does the arrangement of the superior olivary complex encode interaural level difference?

Answer 34

It is a balance between excitation from the CN on the same side and inhibition from the opposite side

Question 35

What was the Jeffress model in 1948 about time difference encoding?

Answer 35

Coincidence detector neurones fire most when the inputs from both sides arrive simultaneously. There are delay lines which mean that the location of the sound determines in which cell the signals meet

Question 36

What are the problems of the Jeffress model 1948?

Answer 36

No evidence of observable delay line organisation, no representation over frequency, no spatial representation of physiological range of delay

Question 37

What did Brand et al 2002 suggest was a better mechanism?

Answer 37

It involved inhibition and computation from globular bushy cells and the MnTB and LnTB

Question 38

What was used to block glycinergic inhibition of the MSO?

Answer 38

Strychnine

Question 39

How did Strychnine show that cells responded best when to ITDs?

Answer 39

Because removing this meant that cells fire more when there was a delay of 0. So the inhibition causes the cells to fire with their peak at a delay outside physiological range

Question 40

At what part of the MSO do the excitatory connections from spherical bushy cells synapse?

Answer 40

The dendrites

Question 41

At what part of the MSO do the inhibitory connections from MnTB and LnTB synapse?

Answer 41

The cell body

Question 42

What is the largest synapse in the body?

Answer 42

The calyx of Held

Question 43

What reduces the delay from the inhibitory connection?

Answer 43

The calyx of Held synapse is very fast and the glycinergic synapse is at the cell body. this achieves maintenance of phase locking

Question 44

What does vertical sound localisation involve?

Answer 44

Interference patterns

Question 45

What are the two components of interferance?

Answer 45

Sound going directly into the ear canal and sound that is reflected from the pinna

Question 46

What type of cells in the dorsal cochlear nucleus are selective for position of spectral notches?

Answer 46

Pyramidal cells