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HESP634 > AN > Flashcards

AN Flashcards

1
Q

How many sections of the 8th nerve are there? What are the sections? What is the mnemonic that helps remember which part section is above the other?

A
  • 4
    • Anterior/superior: CN VII
    • Anterior/inferior: cochlear nerve
    • Posterior/superior: vestibular nerve
    • Posterior/inferior: vestibular nerve
  • 7up/coke down
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2
Q

What is the anatomical pathway that the auditory nerve fibers are attached to the hair cells?

A
  • IAM via the habenula perforata

- Reaches through the bony/perforated modiolus to the spiral lamina

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3
Q

What is a ganglion?

A
  • Cluster of neuron-like cells outside the CNS

- Spiral ganglion: neuron-like cochlear cells

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4
Q

What is the auditory nerve innervation density as a function of frequency?

A
  • High frequency: high density ANFs

- Low frequency: low density ANFs

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5
Q

How many auditory nerve fibers are there in a human?

A

~30,000

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6
Q

What percentage of AN fibers are type I?

A

-90-95%

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7
Q

What type of connections do type I AN fibers have? Type II?

A
  • Type I: many-to-one connections (1-2 IHCs per ANF)

- Type II: one-to-many connections (1 ANF to ~10 OHCs)

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8
Q

What AN fibers surely encode sound?

A

-Type 1

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9
Q

Where do the afferent and efferent AN fibers connect to IHCs? OHCs?

A
  • IHCs: direct connection to afferent fibers, indirect connection to efferent fibers
  • OHCs: direct connection to both afferent and efferent fibers
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10
Q

Describe the tonotopic organization of the auditory nerve.

A
  • High frequencies are encoded around the periphery/lateral edges
  • Low frequencies encoded at the core
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11
Q

What type of fibers do we know a lot about and why?

A
  • Type I

- Easier to find/record

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12
Q

Most neurophysiological information about the auditory system is conducted in what kind of
experiment? What is measured in these experiments?

A
  • Single cell physiology experiments

- Record single ANF firing to a presented stimulus over time

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13
Q

How is a PSTH generated?

A
  • Record a single ANF firing/spike rates over a specific time period (i.e. 1 ms) over multiple recording
  • Average and bin measurements to create a continuous histogram
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14
Q

How is a period histogram generated?

A
  • To obtain a period histogram, a single-unit electrode should be used to record how often a single auditory nerve fiber spikes over the course of one cycle of the stimulus.
  • The number of spikes recorded can then be compared to the phase waveform of the stimulus
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15
Q

How is an interspike interval histogram generated?

A
  • To obtain an interspike interval histogram, one single auditory nerve fiber’s spikes should be recorded
  • Average number of intervals between spikes can then be calculated and plotted as a function of the interval duration.
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16
Q

Describe the main sections of a primary-like PSTH? Why is it called primary-like?

A
  • Onset, steady state (rate adaptation), recovery

- Simplest neural firing (no modifications/transformations performed)

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17
Q

How does a PSTH get converted to a tuning curve? Response area?

A
  • Take a single point in the PSTH to generate a rate-level function
  • TC: horizontal slice of the rate-level function
  • RA: vertical slice of the rate-level function
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18
Q

Describe the shape of low- and high-frequency tuning curves.

A
  • Low frequency: broad, symmetric

- High frequency: sharp, asymmetric

19
Q

What is the measure of sharpness of a tuning curve? How is it calculated? Is a higher number
sharper or broader?

A
  • Q10
  • CF/BW measured at 10 dB above the peak
  • Higher Q10 = sharper TC
20
Q

Do low-frequency AN fibers have absolutely large tuning? Relatively large?

A
  • Absolute: small

- Relative: large

21
Q

At what spike rates do you subdivide thresholds for ANFs?

A
  • Low: <0.5 spikes/s
  • Mid: 0.5-18 spikes/s
  • High: >18 spikes/s
22
Q

What percentage of ANFs are within 10 dB of absolute threshold?

A

-70%

23
Q

Describe the relationship between spontaneous rate and threshold for ANFs.

A
  • High SR: low threshold

- Low SR: high threshold

24
Q

What is phase locking?

A
  • Time locking neural discharge to the stimulus waveform

- Firing at a preferred phase of the stimulus waveform (rarefactions, not condensations)

25
Q

What is the limit of phase locking for the auditory nerve?

A

-4-5 kHz

26
Q

What is the rate limit for firing for the auditory nerve?

A

-800 Hz

27
Q

Why does the AN only fire in a preferred cycle/phase in response to a sine tone?

A

-Only fires during rarefactions, when BM is lifted upward and ion channels are sheared lateraly

28
Q

Why does the response of an ANF to a click have multiple peaks?

A

-Ringing (temporal smearing)

29
Q

Why does the duration of the response of an ANF to a click get shorter with increasing CF?

A

-As CF increases, period decreases

30
Q

Does the ANF respond at the rate of the input or at the intrinsic rate of the neuron?

A

-Rate of the input

31
Q

How is the characteristic frequency determined for an ANF?

A
  • Firing at the lowest neural threshold

- Compressive nonlinearities

32
Q

What limits the phase locking of an ANF?

A

-Refractory periods following ANF firing

33
Q

What is the dynamic range problem for the AN?

A
  • ANF has a smaller DR than HCs
  • ANF DR: 20-50 dB
  • Human perception DR: 120-140 dB
34
Q

How is the dynamic range problem solved?

A

-Firing of multiple ANFs of various spontaneous rates/DRs to encode full perceptual DR

35
Q

Since compression occurs, what might help us encode/perceive vowels?

A

-Neural firing can be saturated but synchronization will occur at higher intensities

36
Q

What does this suggest about the range of useful formant frequencies?

A

-Can only go up to 4-5 kHz

37
Q

Describe the difference between suppression and inhibition?

A
  • Inhibition is chemical

- Suppression occurs because of something non-chemical that reduces ANF firing rate

38
Q

What is one possible cause of two-tone suppression?

A

-Nonlinear mechanics of the BM and HCs

39
Q

How do you measure the suppressive sidebands of an ANF tuning curve?

A
  • Present a single ANF with tones until you find CF
  • Present probe tone at CF at 10-20 dB SL
  • Introduce second tone of varied frequency/intensity
  • Find where ANF firing decreases by at least 20% following introduction of second tone
40
Q 
Describe the general shape of the response of an ANF nerve fiber to a narrowband noise as a
function of bandwidth?
A

-Increasing BW adds more energy, so neuron fires more until the point at which we are outside the tuning curve → start seeing suppression from neighboring areas

41
Q

Are all ANFs excitatory? Are any inhibitory?

A

-All are excitatory

42
Q

What is the “typical” DR of an ANF?

A

-20-50 dB

43
Q

Briefly explain the volley principle of phase locking.

A
  • Most ANFs can only fire at about 800 Hz because after firing, the nerve has to recover before it can fire again (aka the refractory period)
  • Therefore, multiple ANFs are needed to encode temporal patterns of high frequency tones (record multiple ANFs, sum response to encode total response)
44
Q

Briefly explain how lower than CF input frequencies might produce the largest firing rates of
an ANF.

A
  • On compression → compression, off frequency → linear response
  • Traveling wave is asymmetrical (so lower than CF tone→ large envelope)
  • TW grows as you go down the BM

HESP634 (13 decks)

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