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Neuro SKS > Audition > Flashcards

Audition Flashcards

0
Q

Presbycusis

A

Loss of high frequency hearing
Normal with age
- starts around 20 kHz

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1
Q

Characteristics of sound

A

= pressure wave - expands spherically

Amplitude = intensity
- measure on logarithmic decibel scale (very wide range)
Frequency = pitch
- humans 20 Hz - 20 kHz, peaks at 2-3 kHz (speech)
- higher = dogs, bats, moths; lower = elephants, whales
Complexity = timbre (sum of multiple frequencies)

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2
Q

Structure of ear

A

External = auricle/pinna + meatus
- amplifies 30-100x
Middle - 200x amplification
- large tympanic membrane -> small oval window
- lever action of ossicles
- attenuation - tensor tympani (trigeminal), stapedius (facial)
- damage -> hyperacusis (ex Bell’s palsy)
- Eustachian tubes equalize pressure

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3
Q

Structure of cochlea

A

Scala media - endolymph (high K+) made by stria vascularis
Basilar membrane - different vibration frequencies along length
Organ of Corti = support cells, tectorial membrane
- hair cells (1 inner, 3 outer) - stereocilia and kinocilia (longest)

Scala vestibuli and tympani - perilymph
- connected at helicotrema

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4
Q

Tonotopy

A

Basement membrane - different vibration frequencies

  • thin, rigid at base -> greatest intensity at high Hz (16 kHz)
  • wide, flexible near helicotrema -> low frequency (500 Hz)

Each nerve fiber has greatest intensity at certain frequency
Maintained through cochlear nerve, auditory pathway
-> verticle bands in primary auditory cortex

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5
Q

Hair cell function

A

Basement membrane movement vs tectorial membrane -> Displacement of stereocilia -> mechanosensitive K+ channels

Towards kinocilium -> open K+ -> depolarize -> transmitter release
Away from kinocilium -> less transmitter release

“Transduction”
Relies on high electrochemical gradient from high K+ endolymph (125mV)

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6
Q

Cochlear amplifier

A

Outer hair cells = efferent innervation!

Superior olive -> Ach receptors -> hyperpolarize ->
Voltage sensitive motor protein = “prestin” ->
Lengthens -> less movement of basilar membrane (dec intensity)
(Reverse: depolarization -> shorten -> more membrane movement)

Protect from loud noises
Selectively dampen/enhance frequencies
Inhibited by furosemide

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7
Q

Auditory pathway overview

A

Cochlea -> spiral ganglion -> CN VIII -> cochlear nuclei
Superior olivary nucleus -> inferior colliculus -> medial geniculate nucleus (thalamus) ->
Primary auditory cortex

Cochlear nuclei

  • dorsal - tonotopy
  • postero and anteroventral - intensity
  • ventral -> superior olivary (bilateral) -> localization
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8
Q

Sound localization

A

No way to distinguish front-back

Time delay - can detect 5 microseconds!, use up to 3 kHz

  • medial superior olivary nucleus = coincidence detectors
  • vary length of dendrites -> coincidence -> range of neurons respond to different delays

Intensity difference - used about 3 kHz

  • lateral superior olivary nucleus
  • contralateral input -> medial nucleus of trapezoid body -> inhibitory interneurons (vs stimulation by ipsilateral)

Phase difference - only very low frequency

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9
Q

Inferior colliculus

A

Integration with other sensory inputs

  • > startle reflex
  • > vestibulo-ocular reflex
  • > filter out body sounds
  • > auditory space map
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10
Q

Medial geniculate nucleus

A

Relay to cortex

Specific response to combinations of frequencies
Specific response to time differences

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11
Q

Auditory cortex

A

Primary = superior temporal aka Heschl’s gyrus
- vertical tonopy
Secondary aka “Belt areas” - combinations of sounds
- ventral stream via inferior frontal gyrus - pitch
- dorsal stream via superior frontal, superior parietal - location
Wernicke’s area - understanding speech
- both auditory and visual input

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12
Q

Components of language

A 
Phonemes = sounds (ie letters)
Lexemes = short groups, words

Auditory system must be able to distinguish frequency modulation

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13
Q

Echolocation

A

Bats emit range of frequencies

  • delay = distance (1 ms = 17 cm)
  • Doppler shift = change in frequency = movement (1 kHz = 3 m/s)
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14
Q

Speech areas

A

Broca’s area = production - projects to motor cortex
- aphasia - can’t produce speech
Wernicke’s area = comprehension - visual and auditory
- aphasia -> word salad (can’t understand their own)
- normally use both visual and auditory (ie loud room)
- McGurk effect - mismatch -> third related phoneme
Arcuate fasciculus = white matter tract
- aphasia = similar to Broca’s
Supramarginal gyrus - matches sounds to phonemes
(individual neurons for phonemes)
Angular gyrus - matches graphemes to phonemes

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15
Q

Music perception

A

No centralized area - inferior frontal, both hemispheres, inc Wernicke’s and Broca’s
Combination-sensitive neurons
Present at birth, improves with training

Pitch = frequency
- perfect pitch = labelling of frequencies, 1:10,000, critical period in development
- changes - R temporal cortex
- congenital amusia = tone deaf - can’t detect changes, wrong notes (inferior frontal)
Timbre = spectral and temporal envelopes, harmonic content
- R frontal
Rhythm - L hemisphere

16
Q

Auditory agnosia

A

Can’t identify meaning of non-verbal sound (ie doorbell)

17
Q

Conduction vs sensorineural deafness

A

Conduction = before cochlea
- ex wax blocking, ruptured membrane
Sensorineural - hair cells or nerve

18
Q

Acquired hearing loss

A

Trauma
Infection
Drugs (antibiotics)
Presbycusis

vs genetic - complex, 50 genes - K channels, endolymph production, alignment of cilia

19
Q

Rinne test

A

Bone conduction vs air conduction

Normal: air 2x > bone
Conductive loss: bone > air (bypassing external ear structures)
Sensorineural loss: air > bone but less than normal (compensation)

20
Q

Tinnitus

A

Perception of sound in absence of stimulus
Temporary or permanent

Causes:
Damage from loud sounds
Wax buildup
Antibiotics
Age
Vascular
Cochlea, nerve, cortex
21
Q

Acoustic neuroma

A

Schwann cell tumor
Begins on vestibular nerve -> cochlear involvement
Slow growing -> surgical removal

22
Q

Meniere’s disease

A

Progressive, low frequency loss
Buildup of endolymph (? blockage?)
1:500 people

Tx with salt restriction, diuretics

23
Q

Hair cell regeneration

A 
Can be induced
Epithelial stem cells differentiate
 - transcription factors
 - growth factors
 - transplant stem cells
24
Q

Cochlear implants

A

Microphone -> digital signal -> stimulate nerves throughout cochlea

Timbre: only 50 electrodes -> poor complexity, emotional content (prosody)
Critical period: must fuse auditory and visual information
- barn owls are great localizers due to feathers, ears but show limited plasticity as adults (prism goggles…)
- must diagnose and implant before 2.5 years for good results

Neuro SKS (19 decks)

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