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sensory systems > binaural hearing and sound localisation > Flashcards

binaural hearing and sound localisation Flashcards

1
Q

what happens in the inferior colliculus

A

where horizontal and vertical signals converge

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2
Q

MGN

A

the part of the thalamus specialised to hearing

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3
Q

where do teh spiral ganglion cells project to?

A

the dorsal cochlear nucleus
the posterior ventral cochlear nucleus
the anterior ventral cochlear nucleus

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4
Q

what cells type does the dorsal cochlear nucleus mainly contain?

A

fusiform

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5
Q

what cells does the posterior ventral cochlear nucleus mainly contain?

A

octopus

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6
Q

pathway of the dorsal acoustic stria

A

projects from the DCN

1) sends excitatory input to the contralateral central nucleus of the inferior colliculus

2) projects to the contralateral NLL
the NLL sends inhibitory signals to the central nucleus of the inferior colliculus

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7
Q

pathway of the intermediate acoustic stria

A

projects from the PVCN

1) sends excitatory input to the central nucleus of the inferior colliculus

2) projects to the NLL
the NLL sends inhibitory signals to the central nucleus of the inferior colliculus

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8
Q

what is the main cell type in the PVCN?

A

octopus

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9
Q

what are the main cell types in AVCN?

A

spherical bushy and globular bushy

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10
Q

what is the tonotopic organisation of hair cells?

A

highest frequency at the base and lowest frequency at the apex

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11
Q

where is the tonotopic organisation of the basilar membrane (hair cells) conserved?

A

in the spiral ganglion cells that are innervated by the inner hair cells of the cochlear, at the cochlear nucleus and at all levels up to the auditiry cortex

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12
Q

what frequencies does phase locking occur at?

A

20Hz- 4000 Hz

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13
Q

what frequencies does tonotopic firing occur at?

A

4000Hz - 20,000 Hz

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14
Q

what is phase locking?

A

the frequency of the sound wave is low enough that the ganglion cells can fire action potentials in time locked onto the frequency of the soundwave

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15
Q

what is the maximal firing rate of a neuron/ what is the maximal frequency for phase locking?

A

1000Hz

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16
Q

what is the volley theory?

A

phase locking that occurs at low frequencies that are larger than 1000 Hz
neurons cannot respond to every wave
groups of spiral ganglion neurons respond to the same part of a wave but they dont respond to every wave
combination of the neurons code for frequency of the sound wave
coded for by the amount of neighbouring spiral ganglion cells that get activated

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17
Q

what happens to spiral ganglion cells activation in the volley theory as frequency increases?

A

the basilar membrane will vibrate the sides more, so more neighbouring spiral ganglion cells will become activated

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18
Q

frequency range for the volley theory

A

1000Hz- 4000Hz

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19
Q

when wavelength is smaller than barrier width

A

shadow generated behind the barrier

20
Q

shadow

A

area where sound is quieter behind a barrier

21
Q

when wavelength is larger than barrier width

A

wave diffracts around the barrier
travels as if the barrier isn’t there

22
Q

what size barrier does the human head generate?

A

0.2m

23
Q

at what frequencies is the wavelength of sound larger than 0.2m? (diffracts)

A

20Hz to 1500Hz

24
Q

what is the delay of sound from the left to right ear when sound when wavelength >0.2m

A

0.6ms

25
Q

why can we rely on interneural timing differences when wavelength is <0.2m

A

the wavelength will reach the left ear and the right ear before the next wavelength appears

26
Q

at what frequencies is a shadow generated behind the head?

A

1500Hz- 20,000 Hz
wavelength <0.2m

27
Q

what two mechanisms determine sound direction

A

interneural level difference (ILD)
interneural timing difference

28
Q

what frequency can ILD be used for?

A

greater than 1500Hz

29
Q

what frequency can ITD be used for

A

less than 17000 Hz

30
Q

where are there neurons sensitive to different interneural timing delays

A

Medial superior olive

31
Q

what time delay can the neurons in teh MSO discriminate between?

A

0.11 msec
giving a precision of 2*

32
Q

interneural timing delay neural pathway

A

1) Sound from the left side initiates activity in the left anterior ventral cochlear nucleus.

2) projects to the ipsilateral and contralateral medial superior olive

3) Very soon, the sound reaches the right ear, initiating activity in the right AVCN
.
Meanwhile the first impulse has travelled farther along its axon

3) Both impulses reach a olivary neuron at the same time, and summation of synaptic potentials generates an action potential

  • Timing difference from left and right ears leads to summation of signals at the neuron selective for specific time difference
33
Q

why is summation of signals in the medial superior olive necessary?

A

either signal alone creates an EPSP, but not large enough to reach threshold for an action potential

34
Q

pathway of ITD after the MSO

A

MSO projects to CNIC
projects to MGN
projects to auditory cortex

35
Q

ILD: AVCN projects to

A

ipsilateral LSO (glu, excitatory)
contralateral MNTB (glu, excitatory)

36
Q

ILD: MNTB projects t0

A

LSO on the ipsilateral side (Gly, inhibitory)

37
Q

MNTB stands for

A

medial nucleus of trapezoid body

38
Q

what is the role of the LSO neuron

A

calculate the difference between the inhibitory and excitatory signals sent by each ear

39
Q

if the volume is the same on either side of the ear?

A

equal signals will reach the auditory cortex

40
Q

if the sound reaching the left ear is louder than that reaching the right ear?

A

the signal will be greater in the right auditory cortex

41
Q

ILD: where does the LSO project to?

A

ipsilateral CNIC (inhibitory, gly)
contralateral CNIC (excitatory, glu)

42
Q

what is sound localisation in the vertical plane determined by?

A

differences in direct and reflected sounds due to teh pinna

43
Q

what can lead to a lost ability to detect direction of sound in the vertical plane?

A

sticking a tube in the ear or taping the pinna

44
Q

neural pathway of vertical sound processing

A

1) Processed by the dorsal cochlear nucleus
-Has different layers of processing differences in the direct sound and the reflected sound, so it can work out what vertical orientation the sound came from

2) Send the information contralaterally to the central nucleus of the inferior colliculus, where it integrates with the horizontal signal

3) projects to the MGN and then the auditory cortex

45
Q

features of sound that aid determination of direction in the vertical plane

A
  • Most sounds aren’t pure tone, have different varying frequencies
  • At different vertical planes, sounds have different spectral pattern

sensory systems (17 decks)

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