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HNNS > HNS39 Audition > Flashcards

HNS39 Audition Flashcards

1
Q

Cochlea location

A

Temporal bone

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2
Q

2 features of sound

A
  1. Tone (frequency)
    - Nervous system
  2. Location
    - Interaural time delay (too short to be distinguished)
    - Nervous system
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3
Q

***Ascending Auditory pathway

A

記: SCSLIM

Cochlea
—> ***Spiral ganglion
—> Cochlear nerve CN8
—> ***Cochlear nucleus
—> ***Superior olive (Medulla)
—> ***Lateral lemniscus
—> ***Inferior colliculus (Midbrain)
—> ***Medial geniculate nucleus (Thalamus) (Lateral geniculate nucleus: Vision)
—> Auditory cortex
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4
Q

Central auditory pathway features

A

Anatomical characteristics:
1. ***Tonotopic projections (Cochlea)

  1. ***Bilateral, Parallel networks, Crossed connections
    —> allow notes to be compared (L/R ear) —> determine location
    —> unilateral brainstem lesion —> hearing still ok
  2. Hierarchical organisation
  3. Expansion in cell population in Inferior colliculus
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5
Q

Common hearing disorder

A
  1. Tinnitus
    - extreme noise
    - infection
  2. Hereditary
  3. Ototoxicity
  4. Tumour
  5. Temporal bone fracture
    - head trauma
    - location of fracture —> determine conductive / sensorineural hearing loss
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6
Q

2 types of hearing loss

A
  1. Conductive hearing loss
    - middle ear defect
  2. Sensorineural hearing loss
    - sensory pathway / CNS defect
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7
Q

External ear function

A

Collection / Localisation / Modification of sound

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8
Q

***Middle ear function

A
  1. Impedance matching
    - Air-borne vibration (External auditory canal) to Peri-lymph vibration (Cochlea)
    —> Area-ratio difference (Tympanic membrane (large) vs Oval window (small))
    —> Lever action of ossicles (Malleus, Incus, Stapes)
  2. Sound attenuation
    Middle ear muscle **reflex —> modify **alignment of ossicles —> alter energy transmission:
    —> ***Attenuate low frequency
    —> Protect inner ear
    —> Improve speech discrimination in noise (Neural mechanism can also help)
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9
Q

***Cochlea structure

A

3 tubes:

  1. Scala vestibule (upper)
    - Perilymph
    - Oval window —> Conduct sound into Cochlea
  2. Scala tympani (lower)
    - Perilymph
    - Pressure release —> Round window
  3. Cochlear duct
    - Endolymph (produced by Stria vascularis, high in K)
    - Tectorial membrane (bony structure over hair cells, attach at spiral limbus)
    - Organ of Corti: Hair cells (Inner: 1 row + Outer: 3 rows)
    - Basilar membrane (attach at osseous spiral lamina + spiral ligament)
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10
Q

***Sound pathway in middle and inner ear

A

Middle ear:
Malleus —> Incus —> Stapes —> Oval window

Inner ear:
Perilymph vibration (Scala vestibule)
—> Endolymph vibration (Cochlear duct)
—> Basilar membrane displacement
—> Hair cells move (sitting on Basilar membrane, touching upper Tectorial membrane)
—> Shearing force of cilia (Cilia被Tectorial membrane扯向不同方向)
—> Movement of cilia bundle
—> Pressure-sensitive K channels (on tip of cilia) open
—> K enter hair cells (high conc of K in endolymph)

Pressure release:
—> Perilymph vibration (Scala tympani)
—> Round window bulging

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11
Q

***Sensory transduction

A

Sensory stimulus conveyed to readable message by nervous system

Mechanical displacement:
Air vibration —> Fluid vibration —> Mechanical movement —> Shearing force of cilia

Electrical signals:
Pressure-sensitive K channels (on tip of cilia) open
—> K enter hair cell (high conc of K in endolymph)
—> Depolarisation
—> Voltage-gated Ca channels open
—> Ca rush in
—> Release of Glutamate within synaptic vesicles
—> Excitatory action at CN8
—> Generator potential —> Action potential along CN8
—> Auditory afferent to Cochlear nucleus

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12
Q

Outer and Inner hair cells

A

Outer hair cells (3 rows):

  • 10-100:1 afferent connection (100粒cell:1條nerve)
  • innervated by 5% afferent

Inner hair cells (1 row):

  • Main transduction of sound
  • 1:10 afferent connection
  • innervated by 95% afferent

Afferent:
Auditory signals to Cochlear nucleus

Efferent:
Cell bodies in brainstem (Superior olivary nucleus) —> modulate length of hair cells

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13
Q

***Processing of sound frequency in Cochlea

A

Basilar membrane (~棒球棍):

  • Narrow + Stiff + Short stereocilia in base —> High frequency sound cause maximum vibration in base
  • Wide + Floppy + Long stereocilia in apex —> Low frequency sound cause maximum vibration in apex

—> **Tonotopic pattern (place-coding): **Frequency of incoming sound determines Peak of travelling wave
—> wave ***subsides rapidly (sharp cut-off) beyond maximum displacement towards apex

Example:
Middle frequency sound —> Maximal displacement of Basilar membrane in middle

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14
Q

**Processing of sound frequency in Cochlea **Nerve

A

Every nerve has its own receptive field
—> Fire action potential at respective **Frequency + **Intensity of sound

***V-shaped tuning curve (boundary of responsive area)
- Wide top (high frequency cells can still be activated by high intensity sound despite low frequency)
—> relatively poor discrimination
—> for Crude collection of sound

Frequency selectivity

  • Characteristic frequency of a single cochlear nerve where it is stimulated even at low sound intensity (好細聲都收到)
  • Tip of V-shaped tuning curve
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15
Q

Frequency discrimination up Ascending Auditory pathway

A

Higher discrimination at Superior olive, Auditory cortex (highest)
—> progressive sharpening of V-shaped receptive field (narrow top, small area)
—> enhances **frequency discrimination
—> information narrows down going up higher centres (i.e. less information can be transmitted upwards)
—> **extraction of information becomes better

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16
Q

Cochlear implant

A

For patients with hair cells defect

Microphone to collect sound
—> Sound processor
—> Electronic impulses to cochlear implant
—> Stimulating electrodes (Low frequency electrode connect to apex, High frequency electrode connect to base)
—> Activate CN8

17
Q

Modulation of sound intensity

A
  1. Organ of Corti
    - sit on Basilar membrane
    - hair cells hanging on Organ of Corti
    - mechanical layout (intrinsic, cannot be modified) —> Amplifies small vibration
  2. **Superior olive (Medulla)
    - Medial olivocochlear neuron
    —> innervate motor proteins of **    outer hair cells (NOT inner!!!)
    —> efferent-induced depolarisation
    —> **shorten cell bodies of outer hair cells
    —> ↑ sensitivity of hair cells
    —> ↑ displacement of Cilia bundle
    —> ↑ sound intensity
    —> detection of weak auditory signal against background noise
    —> **    Selective filtering / Attention (in-build mechanism / cocktail party phenomenon)
Efferent / Descending pathway (掉返轉):
Auditory cortex
—> Medial geniculate body (Thalamus)
—> Inferior colliculus
—> Lateral lemniscus
—> Superior olive
—> Cochlear nucleus
—> Spiral ganglion
—> Cochlear nerve
18
Q

***Processing of sound frequency in Cochlear nucleus

A
  1. **Temporal pattern analysis
    Cochlea nucleus contain cells of different shapes
    —> cell having same neural response as Cochlear nerve + other cells that respond at different time frame
    —> sound **    segregated into different parts
    —> allow higher centre to ***compare notes of original pattern with other different patterns
    —> analysis of Temporal pattern
  2. ***Frequency analysis
19
Q

***Processing of sound frequency in Superior olive

A

Afferent innervation from left and right side (Directional cues)
時間, 地點, 聲量

  1. Basic **binaural sound processing
    - compare **    Time + ***Intensity signals from 2 ears
  2. Extract ***gross spatial information
    - higher centres needed for accurate localisation
20
Q

Inferior colliculus

A
  1. ***Reflex centre:
    - Novel sound —> Head orientation
    - Loud sound —> Startle response
    e. g. contract reflex in neck muscles
  2. Detect FM (frequency-modulated) + AM (amplitude-modulated) sounds in speech
21
Q

Thalamus (Medial geniculate body)

A

Ascending relay station

22
Q

Primary auditory cortex

A

Temporal lobe, Below Lateral sulcus (Sylvian fissure)

Microscopic arrangement:

  1. Functional columns (areas 41, 42) —> Characteristic frequencies —> Iso-frequency bands (i.e. detect same frequency within same column)
  2. Rows —> R/L ear alternating —> Binaural bands

—> ***Accurate localisation of sound in space

23
Q

Wernicke’s area + Broca’s area

A

Processing of complex sound e.g. language

Wernicke’s area:

  • Recognition of language —> send projection to Broca’s area
  • Temporal lobe (area 22) (mostly in dominant hemisphere)

Broca’s area:

  • Production of speech, Perception of language
  • Frontal lobe (area 44, 45) (mostly in dominant hemisphere)

Dyslexia: dysfunction in Broca’s area

24
Q

***Summary of functions of components of Auditory pathway

A
  1. Cochlea:
    - **Frequency processing —> Longitudinal variation in Basilar membrane —> **Tonotopic representation in Cochlea
    - ***Intensity processing: Organ of Corti + Outer hair cells
  2. Cochlear nerve:
    - Receptive field —> **V-shaped tuning curve —> Characteristic frequency (locus of hair cell on Basilar membrane)
    - Nerves are sharply tuned to exclude frequencies above CF —> discrimination of very soft (near threshold) tones with slightly different frequencies
    - **    Progressive sharpening of V-shaped receptive field up ascending pathway —> frequency discrimination —> extraction of information
  3. Cochlear nucleus:
    - **Temporal pattern analysis
    - **    Frequency analysis
  4. Superior olive:
    - Basic **binaural sound processing
    - Extract gross **    spatial information
  5. Inferior colliculus:
    - **Reflex centre
    - Detect **    FM/AM sounds in speech (+ descending projection from cortex to modulate ascending signals)
  6. Thalamus (MGB):
    - Ascending relay station (+ descending projection from cortex to modulate ascending signals)
  7. Primary auditory cortex: Accurate ***localisation of sound in space
  8. Wernicke’s area + Broca’s area: Processing of complex sound
25
Q

Auditory tests

A
  1. Pure tone audiometer:
    - measure ***hearing threshold of a conscious subject in terms of intensity (deciBel Sound Pressure Level) and frequency (Hz)
  2. Brainstem auditory evoked response (BAER):
    - ***click-evoked neural activity of the auditory pathway for assessing hearing ability of subjects esp. infants

HNNS (58 decks)

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