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Neuro > Auditory System > Flashcards

Auditory System Flashcards

1
Q

Inner hair cells

A

Receptive cells in cochlea responsible for converting vibration into a nerve signal (most important)

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2
Q

Outer hair cells

A

Act as a cochlear amplifier.
Regulate vibration of tectorial membrane and help us detect the signal correctly

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3
Q

High frequencies produces vibration of

A

Base of the cochlea

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4
Q

Low frequencies produces vibration of

A

Tip of the cochlea

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5
Q

Mechanisms of frequency coding

A

Basilar membrane vibration
Electrical impulse (HC) to auditory nerve

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6
Q

Electrical impulse (HC) to auditory nerve - relationships

A

APs in VIII CN maintain 1:1 relationship: 1 AP per vibration up to certain frequencies —> + 5 kHz, AP gets sent every 2 - 3 vibrations (1:n relationship)

Important for perceiving low frequencies (fundam freq and harmonics) —> music, different notes

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7
Q

Auditory neurons - location

A

Soma in spiral ganglion (middle of the cochlea) - ascend through the nerve - brainstem

In the cochlea, HC in Organ of Corti synapse w/ auditory neurons

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8
Q

Types of auditory neurons

A

Type I neurons = synapse w/ 1 single inner HC each ( +precise detection of sound)

Type II neurons = synapse w/ many outer HC (- precision in the message as it picks up many sources)

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9
Q

General characteristics of the auditory pathway

A

Tonotopic organization (pitch freq represent at any point)

Multiple commissure (connections between both sides of pathway)

Parallel processing (sub pathway for each type of info that converge in inf colliculus)

Descending projections (every higher projection controls lower projections)

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10
Q

Cochlear nuclei - parts, location

A

Ventral cochlear nuclei (VCN)
Dorsal cochlear nuclei (DCN)

Located in the junction between medulla and pons
VII + VIII CN enter/exit brainstem -> pontocerebellar angle

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11
Q

Cell types in cochlear nuclei

A

Many types

VIII enters the nucleus = axon diverges and synapse w/ several types of cells —> each cell type receive specific type of info

From 1 input (1 nerve fibre), we need parallel processing of many types of info —> nucleus = major relay point (1st)
- Temporal processing = synapse in a region with specific cells
- Frequency processing = synapse in structures related to frequency recognition

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12
Q

Auditory nerve characterization

A

Peristimulus histogram —> time curve = measures discharges along time

Running curve —> how frequency specific a neuron is (they loose selectivity as the sound intensity increases)

Rate-intensity curve —> how a neuron responds to changes in the intensity of sound

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13
Q

Superior olivary complex - location, function

A

After the cochlear nucleus
Localizing sound

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14
Q

Superior olivary complex - nuclei

A

Medial olivary nucleus
Lateral olivary nucleus
Medial nuclei of the trapezoid body

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15
Q

Periolivary regions

A

1st areas originating descending pathways: the olivocochlear path

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16
Q

Olivocochlear path

A

Project to the cochlea itself and act on HC.
Important for the action of outer HC (contract) -> regulated by superior olivary complex

17
Q

Mechanisms for lateral localization of sound

A

Lat sup olive and med nucleus of the trapezoid body

Med sup olive

18
Q

Lateral superior olive and medial nucleus of the trapezoid body

A

Intensity differences between ears (level detector)
Useful for high pitch sounds
Best developed in humans

19
Q

Medial superior olive

A

Detects phase / time differences between areas) —> can only be done when different parts of sound wave are contacting each ear at = time ↴

Useful for low pitch sounds (where wavelength is broad = each wave can be in contact w/ 2 ears at = point in time)

20
Q

Differences in intensities are useful for

A

High pitched sounds

21
Q

Phasic differences (differences in time) are useful for

A

Low pitch

22
Q

Lateral localization for LOW-PITCHED sounds

A

Neurons in med sup olive receive R + L axons of different lengths. Different pairs of neurons.

  • 1st pair (lt = rt): sound at = time —> sound is reaching 2 ears at the = time, in = manner
  • 2nd pair (lt < rt): sound at = time —> sound is reaching 1 side (L in this case) later than at the R side
  • 3rd pair (lt «< rt), even + time to reach the other ear
23
Q

Lateral localization for HIGH-PITCHED sounds

A

For intensity: from one side we excite, from the other the signal is inhibited. Say we are on the R side:
- Ipsilateral neuron reaches lat sup olive nucleus (LSO)
- Contralateral neuron, from the L ear, reaches the med nucleus of trapezoid body (NMTB)

Both nuclei are interconnected.

If signal coming from 1 side is stronger than the other, the other will be inhibited.
Neuron coming from ipsilateral side (right) is firing at higher rates (it’s perceiving + intensity) -> LSO activated on the R side, NMTB inhibited = sound coming from R.
In L side, opposite will happen (contralat neuron coming from R is conveying + APs) —> NMTB on L activated and L LSO inhibited.

24
Q

Descending auditory pathways

A

Olivocochlear bundle
Cortico-thalamic projections (to medial geniculate body)
Cortico-collicular projections (to inferior colliculus)
Descending projections from the Inferior colliculus (to cochlear nuclei & sup olivary complex)

25
Q

Nuclei of lateral lemniscus

A

Ventral nucleus of LL: involved in temporal processing of sound, only receives input from contralateral ear

Dorsal nucleus LL: unknown function, sends efferences to ipsilateral and contralateral inferior colliculi

26
Q

Inferior colliculus

A

Point where all the auditory pathway converges

27
Q

Inferior colliculus parts

A

Central nucleus
- frequency processing
- laminae —> each processes a specific frequency (tonotopic organization)
- functional groups within each lamina

Cortices
- surrounds the nucleus
- more integrative function
- receive afferences from central nucleus

28
Q

Superior colliculus

A

Motor structure that integrates sensory inputs from different pathways to give off efferents.

No exactly part of auditory pathway, but related

29
Q

Superior colliculus function

A

Orient responses (gaze) towards images or sound.
Respond to different stimuli by moving our head.

30
Q

Auditory pathways final stages

A

After converging at inf colliculus, fibres are sent to thalamus —> medial geniculate body (ventral + dorsomed regions)

31
Q

Ventral MGN

A

Tonotopic distribution
Fibres coming from the central nucleus of the IC
More frequency specific (narrow tuning curves)
Projects to the primary auditory cortex

32
Q

Dorsal MGN

A

Fibres coming from the cortices of the inferior colliculus
Less frequency specific
Go to cortex and 2º auditory areas (small associative areas)

33
Q

Auditory Cortex (temporal lobe)

A

Primary auditory cortex (area 41)
Secondary auditory cortex = area 42

34
Q

Secondary auditory cortex

A

Concerned with memory and sound classification
Multimodal integration areas, auditory not specific responses may be present.

35
Q

Primary auditory cortex

A

Tonotopic organization w/ binaural (from both sides) responses

Auditory cortices from 2 sides are highly connected and communicated through corpus callosum (contralat connections)

Cortical, thalamic and collicular projections

Neuro (23 decks)

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