Hearing L3

Question 1

do you understand phase locking?

Answer 1

Neurones dont fire every stimulus

but maybe once every 3 peaks in wave

Overall frequency of APs = sound frequency, more APs = more sound

Question 2

T or F

Note that when an action potential does occur it is always phase- locked.

Answer 2

T

Question 3

Auditory-nerve fibres have been divided into groups based on

Answer 3

Auditory-nerve fibres have been divided into groups based on their spontaneous discharge rate (SR - defined as the discharge rate of an auditory neuron in the absence of controlled acoustic stimulation).

Fibres with the lowest thresholds (the most sensitive) have the highest spontaneous rates,

whereas those with the highest thresholds (least sensitive) have the lowest SRs.

Question 4

An auditory-nerve fibre’s threshold determines ….

Answer 4

An auditory-nerve fibre’s threshold determines its dynamic range

Question 5

Low threshold fibres have the ________ dynamic range, high threshold fibres have the ______ dynamic range.

Answer 5

Low threshold fibres have the narrowest dynamic range, high threshold fibres have the widest dynamic range.

Question 6

interesting figure regarding SR

Answer 6

Question 7

describe the olivocochlear efferent innervation of system

Answer 7

The olivocochlear system supplies descending fibres from the superior olive to the cochlea.

divided into lateral and medial

Question 8

describe the lateral olivocochlear system

Answer 8

• cell bodies around the lateral superior olive
• temrinates on dendrites of auditory nerve fibres
  
  • 3 hypothesis of function

Question 9

describe the medial olivocochlear system

Answer 9

cell boies medail to lateral superior olive - in periolivary region of superior olive

terminates directly onto the outer hair cells

Question 10

The olivocochlear efferent system - what does it mena?

Answer 10

The brain is therefore able to influence the output of both sets of receptor cells.

Question 11

describe how its hypothesized that the lateral olivocochlear eferent system protects us from loud sounds

Answer 11

• Threshold following loud sounds (minutes @100Db) is increased
• this loss recovers over hours to days - temporary threshold shift
• If the tone exposure is accompanied by electrical stimulation of the medial olivocochlear system, the increase in threshold is greatly reduced.
• A similar protection from an increase in thresholds is seen when the exposure to a loud stimulus in one ear is accompanied by an acoustic stimulus in the other ear. This protection disappears if the medial olivocochlear system is disrupted e.g. by sectioning the olivocochlear bundle at the floor of the fourth ventricle.

Question 12

describe the hypothesis of how the alteral olivocochlear system: improving detection of sounds in noise (anti- masking)

Answer 12

• Electrical stimulation of the medial olivocochlear system can improve the detectability of signals in noise.

*

Question 13

describe what happesn to vowel sounds when olivocochlear bundle is cut

Answer 13

behavioural experiments which indicated that the detection of vowel sounds is left intact when the olivocochlear bundle is cut but the discrimination of vowel sounds is impaired.

Question 14

is the cochlear nucleus describes as the retina of the auditory system?

Answer 14

yes

Question 15

cochlear nucleus cells are characterised by?

Answer 15

Large end bulb of Held synapses

Question 16

These cells are characterised by large end-bulb of Held synapses - these synapses are amongst the _______ in the brain

Answer 16

These cells are characterised by large end-bulb of Held synapses - these synapses are amongst the largest in the brain

Question 17

do some cells in the cochlear nucleus show lateral inhibition

Answer 17

yess

• analogus to the visual system!!

Question 18

in the cochlear nucleus are the cells mainly doing alot of summing of information from many auditory fibres

Answer 18

yessss

Question 19

do you know the audtiory path throguh the brain?

Answer 19

good

i hope so!

Question 20

what is the inferior colliculi the equiverlent of to the visual system

Answer 20

V1

Question 21

what does the ‘The endbulb of Held’ look like

Answer 21

Question 22

While much of the cochlear output may be modified by the cochlear nucleus and higher levels in the auditory pathway many response properties of auditory-nerve fibres e.g. ________, are preserved at levels as high as the cortex.

Answer 22

While much of the cochlear output may be modified by the cochlear nucleus and higher levels in the auditory pathway many response properties of auditory-nerve fibres e.g. tonotopicity, are preserved at levels as high as the cortex.

Question 23

. The first site of binaural convergence of the cochlear nucleus output is the…

Answer 23

. The first site of binaural convergence of the cochlear nucleus output is the superior olivary complex (SOC).

Question 24

There are three main superior olivary complex (SOC) nuclei; what are tehy?

Answer 24

the lateral superior olive (LSO), the medial superior olive (MSO) and the medial nucleus of the trapezoid body (MNTB or MTB).

Question 25

The Morphological and physiological characteristics of an end-Bulb of Held. The extracellular action potential has a characteristic 3 component shape;

Answer 25

pre-synaptic potential (PP) from the large end-bulb,

an excitatory post-synaptic potential (EPSP)

and a somatic action potential (SAP)

Question 26

The auditory midbrain consists of …

Answer 26

The auditory midbrain consists of the inferior colliculus (IC) and the superior colliculus (SC).

Question 27

where is sound localisation computed?

Answer 27

not in the basilar membrane

There is no representation of auditory space along the basilar membrane - this must be computed by the central auditory pathway

Question 28

We are able to discriminate sounds that are __apart in azimuth (or horizontal plane) and ___° apart in elevation (or vertical plane).

Answer 28

We are able to discriminate sounds that are 2°apart in azimuth (or horizontal plane) and 10° apart in elevation (or vertical plane).

Question 29

can we use intensity as a cue for calculating distance?

Answer 29

no

Question 30

While sound localisation is possible with one ear better results are obtained by combining information from the two ears.

why?

Answer 30

While sound localisation is possible with one ear better results are obtained by combining information from the two ears.

The brain can compare the differences in both time and intensity of a sound arriving in both ears.

Question 31

describe Interaural time differences (ITDs)

Answer 31

For all directions other than 0° azimuth sound must travel further to reach one ear than the other. For humans the maximum time difference is 660μs (90° & 270° azimuth) and the minimum detectable time difference is 10 μs.

Interaural phase differences also provide a cue for localisation of continuous sounds below about 1.4 kHz. This limit is imposed because the size of the head causes phase to become ambiguous.

Question 32

Interaural phase differences also provide a cue for localisation of continuous sounds below about 1.4 kHz. This limit is imposed because….

Answer 32

Interaural phase differences also provide a cue for localisation of continuous sounds below about 1.4 kHz. This limit is imposed because the size of the head causes phase to become ambiguous.

Question 33

describe the interaural time difference pathway

Answer 33

The Medial superior olive receives input from spherical bushy cells of the anteroventral cochlear nucleus from both sides of the brain and uses the principles of coincidence detection and delay lines to measure interaural time differences in different frequency bands.

Each neuron is maximally sensitive to a single time disparity (best ITD) and different neurons are selective for different disparities. The axonal path to the neurons increases systematically along the array but in the opposite direction for the two ears. Therefore, the place of a neuron in the MSO signals the ITD to which the neuron responds best.

Question 34

describe how sound shadows can be used to localise sound

Answer 34

At high frequencies the more distant of the two ears is shadowed by the head and the sound reaching this ear is less intense. The interaural intensity difference is insignificant below about 1 kHz and reaches a maximum of about 20 dB for high frequencies at 90° and 270°azimuth (Fig. 34).

Question 35

describe the Neural encoding of Interaural level differnces (ILDs)

Answer 35

The LSO receives excitatory input from bushy cells in the ipsilateral VCN and inhibitory input from the ipsilateral MNTB. The ipsilateral MNTB receives excitatory input from the bushy cells of the contralateral VCN. Note that the cells in the MNTB are also characterised by giant synaptic endings allowing for the fast, precise transmission of temporal information

The output of neurons in the LSO therefore reflects the balance of ipsilateral excitation and contralateral inhibition (Fig. 36).

Question 36

what is duplx theory?

Answer 36

In summary,

for pure tones it appears that localisation in the azimuthal plane depends on:

• interaural time differences at low frequencies
• interaural intensity differences at high frequencies.

This is known as the duplex theory.

Question 37

fat

Answer 37

mamba