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NAB > 4d. Central Auditory System > Flashcards

4d. Central Auditory System Flashcards

1
Q

Afferent Innervation of the Cochlea

- IHC Neurotransmitter

A

IHCs release glutamate that acts on AMPA receptors on type I ganglion cells.

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2
Q

Afferent Innervation of the Cochlea

- IHC Neurones

A

Synapse with 90% of auditory nerve fibres, which are type I ganglion cells

Each type I ganglion cell connects to only 1 IHC and each IHC can be innervated by up to 20 type I ganglion cells

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3
Q

Afferent Innervation of the Cochlea

- OHC Neurones

A

Synapse with 10% of auditory nerve, which are type II ganglion cells, which are un-myelinated

Each type II ganglion cell innervates many OHCs

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4
Q

Afferent Innervation of the Cochlea

- Afferent Ganglion Cells

A

Bipolar spiral ganglion cells

Form the cochlear part of cranial nerve VIII (vestibulocochlear).

Travel to cochlear nuclei in the brainstem

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5
Q

Temporal Adaptation

- Location

A

Likely takes place at the hair cell - afferent fibre synapse

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6
Q

Temporal Adaptation

- Description

A

Action potential frequency decreases over time with a steady stimulus

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7
Q

Auditory Nerve Spontaneous Firing Rate

A

60% of auditory nerve fibres have spontaneous firing

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8
Q

Frequency Coding

- 3 Mechanisms

A
  • Labelled line coding
  • Phase locking
  • Lateral inhibition
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9
Q

Labelled Line Coding

A

There are >10,000 overlapping bandpass filters which allow the tonotopicity of the basilar membrane to be preserved from cochlea to cortex

Bandpass filters are narrower at higher frequencies

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10
Q

Labelled Line Coding

- Characteristic Frequency

A

The most sensitive point of the bandpass filter

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11
Q

Labelled Line Coding

- Q10dB

A

Q10dB = CF/Bandwidth 1dB above CF Threshold

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12
Q

Phase Locking

- Reason

A

Low frequency afferents have large bandpass filters so frequency encoding is requires to encode frequencies >3kHz

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13
Q

Phase Locking

- Description

A

Temporal coding that ensures action potentials can only fire during the rising phase of the vibrational stimulus sinusoid, as this is where hair cells are depolarised and neurotransmitter is released.

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14
Q

Phase Locking

- Limitation

A

Action potentials do not fire at every vibrational sinusoid

The upper limit of phase locking is higher than the upper limit of action potential frequency (1,000Hz), which is limited by the refractor period.

Instead fibre recruitment at the upper end of frequencies is required

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15
Q

Lateral Inhibition

- Description

A

Tightens the frequency response by the OHCs

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16
Q

Amplitude Coding

- 2 Methods

A
  • Action potential frequency, while maintaining phase locking
  • Fibre recruitment
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17
Q

Amplitude Coding

- Action potential Frequency

A

Louder sound increases rate of action potential firing while maintaining phase locking

18
Q

Amplitude Coding

- Fibre Recruitment

A

Louder sound increases fibre recruitment

19
Q

Spontaneous Discharge Rate

A

Low threshold fibres:

  • High spontaneous firing rate
  • Narrow dynamic range
  • Synapse on the lateral side of hair cells

High threshold fibres:

  • Low spontaneous firing rate
  • Wide dynamic range
  • Vulnerable to acoustic overstimulation
  • Synapse on medial side of hair cells
20
Q

Parallel Processing in the Cochlear Nucleus

A
  • Neurones that preserve temporal information
  • Neurones that preserve amplitude
  • Neurones that show strong lateral inhibition
21
Q

Parallel Processing in the Cochlear Nucleus

- Temporal Information

A

These neurones have end-bulb of held synapses, which are among the largest synapses in the brain

22
Q

Parallel Processing in the Cochlear Nucleus

- Amplitude Information

A

These neurones have a wide dynamic range and sum information from many auditory nerve fibres

23
Q

Parallel Processing in the Cochlear Nucleus

- Tonotopic Information

A

Tonotopic information is preserved into the cortex

24
Q

Central Pathways

- Scheme

A
  1. Cochlear nucleus in brainstem
  2. Superior olivary complex in the brainstem
  3. Colliculi in the midbrain
  4. Medial geniculate nucleus of the thalamus in the midbrain
  5. Primary auditory cortex
25
Q

Cochlear Nucleus

- Divisions

A
  • Anterior ventral
  • Posterior ventral
  • Dorsal
26
Q

Cochlear Nucleus

- Anterior Ventral Nucleus

A

Travel in the ventral striatum (trapezoid body) to the superior olivary complex (brainstem)

27
Q

Cochlear Nucleus

- Posterior Ventral Nucleus

A

Travel in the ventral striatum (trapezoid body) to the superior olivary complex (brainstem)

28
Q

Cochlear Nucleus

- Dorsal Nucleus

A

Travel in the dorsal stria to the central nucleus of the inferior colliculus (midbrain)

29
Q

Superior Olivary Complex

A

First site of binaural convergence of the cochlear nucleus output

30
Q

Superior Olivary Complex

- Divisions

A
  • Lateral superior olive (LSO)
  • Medial superior olive (MSO)
  • Medial nucleus of the trapezoid body (MNTB)
31
Q

Superior Olivary Complex

- Output

A

Central nucleus of ethanol inferior colliculus (midbrain)

32
Q

Colliculi

- Divisions

A
  • Rostral colliculus

- Caudal colliculus

33
Q

Rostral Colliculus

- Function

A

Cells are spatially selective but no map of the auditory space has been found

34
Q

Caudal Colliculus

- Function

A

Map of auditory space has been found in the deep layers of the caudal colliculus, and is usually aligned with a visual map of space

35
Q

Colliculi

- Output

A

Medial geniculate nucleus in the thalamus (midbrain)

36
Q

Medial Geniculate Nucleus

- Output

A

Auditory cortex

37
Q

Auditory Cortex

A

Tonotopically organised

38
Q

Conscious Auditory Pathway

A
  1. Cochlea nuclei (brainstem)
  2. Medial superior olivary nucleus (brainstem)
  3. Nucleus of the lateral lemniscus (midbrain)
  4. Medial geniculate nucleus in the thalamus (midbrain)
  5. Temporal cortex, specifically the primary auditory cortex
39
Q

Unconscious Auditory Pathway

A
  1. Cochlear nuclei (brainstem)
  2. Nucleus of the lateral lemniscus (midbrain)
  3. Neurones in the midbrain synapse with motor neurones in the brainstem
40
Q

Startle Reflex

- Description

A

Unconscious reflex response to positive and negative auditory stimuli

41
Q

Startle Reflex

- Sensory and Motor Arms

A

Sensory Arm:
Cranial nerve VIII (vestibulocochlear)

Motor Arm:
Cranial nerves III, IV and VI

42
Q

Startle Reflex

- Responses

A

Look towards/away from stimulus
- Cranial nerves III, IV and VI

Move head and neck towards/away from a sound
- Tectospinal tract

Blink or make fascial expression
- cranial nerve VII

NAB (37 decks)

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