Auditory system lecture 15 and 16

Question 1

How many outer hair cells do we have?

Answer 1

12,000 (in 3-5 rows)

Question 2

How many inner hair cells do we have?

Answer 2

3500 (in 1 row)

Question 3

How many nerve fibres make up the auditory nerve?

Answer 3

30,000

Question 4

What percentage of the 30,000 nerve fibres in the auditory nerve are type I?

Answer 4

95%

Question 5

Which cell type are type I fibres associated with?

Answer 5

Inner hair cells

Question 6

How many fibres can 1 IHC have associated with it?

Answer 6

10-15

Question 7

How many cells can 1 type 2 fibre associate with?

Answer 7

Multiple, in different rows

Question 8

Where is the first nucleus of the auditory pathway?

Answer 8

The cochlear nucleus in the pons

Question 9

What are the three nucleus in the cochlear nucleus?

Answer 9

DCN, PVCN and APCN

Question 10

After the cochlear nucleus, where do the fibres go?

Answer 10

The superior olivary complex in the pons

Question 11

At what point do fibres from left and right auditory nerves interact?

Answer 11

The superior olivary complex

Question 12

After the SOC, where do the fibres go?

Answer 12

Through the lateral lemniscus to the inferior colliculus in the midbrain

Question 13

Where is the inferior colliculus?

Answer 13

The midbrain

Question 14

After the inferior colliculus, where do the fibres go?

Answer 14

To the medial geniculate body in the thalamus

Question 15

What is a main difference between the visual and auditory pathways in terms of nucleus?

Answer 15

The auditory pathway has many more nucleus in the midbrain, the visual system has no brainstem involved, just goes from LGN to V1.

Question 16

What are the different steps of the auditory pathway?

Answer 16

Cochlear nucleus (3 parts), superior olivary complex, through the lateral lemniscus to the inferior colliculus to the medial geniculate body of the thalamus, then to V1.

Question 17

Which nucleus of the auditory pathway is in the midbrain?

Answer 17

The inferior colliculus

Question 18

Each ear projects bilaterally, but which is dominant?

Answer 18

The contralateral pathway

Question 19

Describe parallel processing

Answer 19

Fibres go to different regions of the cochlear nucleus which each have distinct cell types which respond differently to different properties of sound. These cells project to different regions of the superior olivary complex also.

Question 20

Where do the parallel connections converge again?

Answer 20

In the inferior colliculus.

Question 21

What is tonotopicity?

Answer 21

The spatial organisation of frequencies

Question 22

Describe the tonotopicity in the AVCN and PVCN

Answer 22

High to low frequencies are arranged dorsal to ventral

Question 23

Why is tonotopicity important?

Answer 23

To ensure precise frequency discrimination is maintained throughout the auditory pathway

Question 24

Describe the tonotopicity of the inferior colliculus

Answer 24

High to low frequencies are encoded in a caudal to rostral direction

Question 25

When recording from inferior colliculus cells, why are they not all V shaped?

Answer 25

They are subject to inhibition and additional processing

Question 26

Which lobe is A1 in?

Answer 26

Temporal lobe

Question 27

What landmarks help identify A1 when removing frontal and parietal lobe?

Answer 27

Heschl's hyrus and Planum temporale

Question 28

What five areas respond to sound?

Answer 28

A1, A2, anterior auditory field (AAF), posterior auditory field (PAF) and Ventral posterior auditory field (VPAF)

Question 29

Why do we have multiple tonotopic maps across these regions?

Answer 29

Each one does different processing of the same sound

Question 30

What are the two strategies for encoding frequency?

Answer 30

Tonotopic organisation and phase locking

Question 31

What is phase locking?

Answer 31

Synchronising the firing of nerve fibres and neurones to the sound waveform

Question 32

At what point of the waveform is there firing?

Answer 32

At the peak

Question 33

In which cells in the cochlear nucleus is phase-locking enhanced?

Answer 33

Bushy cells

Question 34

Why is phase locking enhanced in bushy cells?

Answer 34

There is convergence of multiple auditory nerve fibres onto one bushy cell so the response from this cell follows the pattern of the waveform for tightly.

Question 35

At what frequencies receptor potentials phase locked?

Answer 35

Low frequencies

Question 36

At high frequencies, what signals sound?

Answer 36

The step in receptor potential

Question 37

Temporal coding of frequency is limited to frequencies below...

Answer 37

3-5kHz

Question 38

What is the upper limit of phase-locking in the inferior colliculus?

Answer 38

0.6kHz

Question 39

What is phase-locking important for?

Answer 39

Interaural comparisons for sound localisation

Question 40

What is the determiner on the tuning curve of intensity encoding?

Answer 40

The rate- level function

Question 41

What is the rate level function?

Answer 41

Measures the firing rate of a single nerve fibre at a fixed frequency with increased intensity level

Question 42

What is threshold on the rate level function?

Answer 42

The sound intensity at which the nerve fibre begins firing above spontaneous rate

Question 43

What is the typical dynamic range of an auditory nerve fibre?

Answer 43

40 dB

Question 44

What is dynamic range?

Answer 44

The range of sound intensity over which an auditory nerve fibre increases its firing with increased level.

Question 45

Over how many dB does our hearing cover?

Answer 45

0-120 dB

Question 46

What is the dynamic range problem?

Answer 46

Each auditory nerve only increases firing over a dynamic range of 40 dB, but we can hear a range of 120 dB SPL (a million fold range of sound pressure)

Question 47

How many types of type 1 fibre do we have?

Answer 47

3

Question 48

What are the three types in terms of threshold and spontaneity?

Answer 48

Low threshold high spontaneity, medium threshold medium spontaneity, high threshold low spontaneity

Question 49

What is the threshold of a typical high threshold fibre?

Answer 49

Above 40-60 dB

Question 50

What is different about the rate level function of a high threshold type 1 fibre?

Answer 50

It is linear, not sigmoidal

Question 51

Describe the dynamic range of a high threshold fibre

Answer 51

Wide- covers 40-120 dB

Question 52

Which type of hair cell are these fibres associated with?

Answer 52

Inner hair cell

Question 53

Where do low threshold, high spontaneous firing rate fibres synapse onto?

Answer 53

The pillar face of the inner hair cell (The side facing the outer hair cells)

Question 54

Describe the diameters of the two fibres

Answer 54

Low threshold, high SR are wider, high threshold low SR are thinner

Question 55

Where do the high threshold, low SR fibres synapse onto?

Answer 55

The modular face

Question 56

Which regions of the monkey A1 were found to be concerned with sound localisation?

Answer 56

caudal medial and caudal lateral

Question 57

Which regions of the monkey A1 were found to be specific for vocalisations?

Answer 57

AL and ML

Question 58

Which auditory field, when cooled, removes sound localisation ability?

Answer 58

Posterior

Question 59

Which auditory field is for determining what something is?

Answer 59

The anterior auditory field