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CNS > Unit 9 - Hearing Physiology > Flashcards

Unit 9 - Hearing Physiology Flashcards

1
Q

Structures of ear

Function of ossicles

Function of eustachian tube

A

Ossicles transfer signal from eardrum to inner ear

Eustachian tube -> mouth - equalises pressure between oral cavity and middle ear

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2
Q

Contents of middle ear

A

Air filled (so signal is not reduced)

Eustachian tube equalises pressure

3 auditory ossicles - malleus, incus (anvil), stapes (stirrup)

Connected by tiny synovial joints - amplify vibrations from tympanic membrane to oval window

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3
Q

Why are younger children more susceptible to ear infections

A

Their face is small and the angle of eustachian tube might be too shallow to allow drainage

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4
Q

Relationship between external auditory meatus and malleus

A

EAM is flush with malleus

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5
Q

What structures does the oval window transmit vibrations to

A

To vestibule and on to the cochlea (scala vestibuli)

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6
Q

3 fluid filled compartments of the cochlea

A

Scala vestibuli

Scala media

Scala tympani

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7
Q

Scala vestibuli

A

Perilymph

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8
Q

Scala media

A

endolymph - unusually high K+ conc

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9
Q

Scala tympani

A

Perilymph

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10
Q

Compartment with high [K+]

A

Scala media - endolymph

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11
Q

What is the scala tympani connected to

A

Round window between inner and middle ear

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12
Q

Difference between perilymph and endolymph

A

Perilymph is more viscous than scala media

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13
Q

Where does the organ of corti sit

A

On top of basilar membrane

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14
Q

No of layers of hair cells

A

4, sometimes 5 but single row of INNER hair cells is crucial to our capacity to hear

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15
Q

Where do the cilia of hair cells project into

A

Scala media (endolymph)

Some are longer than others - keno cilium

Embedded in membranous membrane

Scala tympani - vibrations through it

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16
Q

Movement of reissner’s membrane

A

Reissners membrane is rigid - vibrations as they pass through scala vestibuli doesn’t do anything in scala media

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17
Q

Movement of basilar membrane

A

Basilar membrane is elastic - scala tympani underneath moves

Deflection of cilia caused by basilar and tectorial membrane moving but not together

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18
Q

What is found at the base of the cilia

A

Mechanoreceptors - ion channels

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19
Q

What does vibration of stapes cause

A

Vibration of perilymph through oval window

Causes vibration of elastic basilar membrane

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20
Q

Where are hearing receptors found

A

In organ of corti

Hair cells surmount the basilar membrane and are connected to tectorial membrane

Vibrations cause deflection of hairs

Depolarisation or hyperpolarisation

Organ of Corti - 16,000-20,000 hair cells (about 4 rows of 4,000)

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21
Q

What row is responsible for sending signal

A

Inner row of hair cells - 1

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22
Q

Function of outer hairs

A

Signal amplification role?

Focus on a particular aspect of sound?

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23
Q

Movement of membranes

A
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24
Q

Effect of movement of stereocilia

A

Opening/closing of K+ channels

When opened, K+ enters cells - depolarisation (endolymph has high [K+])

collagen fibres connect cilia

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25
Q

Unfurled cochlea (2 and 3/4 turns)

A

Sound frequencies seem to affect basilar membrane at different optimised places

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26
Q

How is frequency sensed

Range of freq heard by young vs old

A

Mainly by “place principle”

Young: 20-20,000 Hz

Old: 50-5,000 Hz

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27
Q

How is loudness sensed

A

By amplitude of response

Spatial summation

Activation of outer hair cells - some signal to brain

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28
Q

Low freq

A

Maximal vibration at tip (helicotrema)

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29
Q

High freq

A

Closer to base

30
Q

Place principle

A

Basilar membrane is not of equal thickness along length of membrane

20-30,000 basilar fibres fixed at 1 end

Thickness & rigidity of membrane decreases from base → helicotrema (tip)

Each freq of stimulation excites maximal motion at a specific position (place) along the membrane

31
Q

Deafness

Different types

A

Prolonged/frequent exposure to excessive loud noise can cause degeneration of hair cells, resulting in high freq deafness

SENSORINEURAL - Problems with neurons/brain - problems with hair cells and pathway that carries sound to auditory cortex

CONDUCTION - Problem is in ear up to point of hair cells - wax in outer ear, fluid in inner ear

Tuning fork on mastoid body can differentiate

32
Q

MOA of hearing aid

A
  • Under mastoid process is fluid filled inner ear - cochlear is there
  • Sit it on mastoid process - amplifies signal
33
Q

What do hearing tests examine

A

Air conduction - outer, middle, inner ear and auditory pathway function

Bone conduction - bypasses the outer and middle ear

Tuning fork tests & audiometry

34
Q

Pure tone audiogram

A
35
Q

Deafness severity

A
36
Q

Neural processing within auditory pathway

A

Inner hair cells synapse on > 90% of ganglion cells - Glu NT

Eighth CN - vestibulocochlear

Signal has phasic and tonic components

37
Q

Overview of auditory pathway

A
38
Q

How do fibres travel in the auditory pathway

A

Majority decussate - contralateral side mostly

Some fibres from each ear go to both side of brain

Collaterals also innervate

  • reticular activating system (sleep wake cycle)
  • vermis of cerebellum (motor part - loud noise can knock you)

Inhibitory retrograde fibres from each level of auditory system back to cochlea - allows tuning in to specific sound (outer row of hair cells)

39
Q

Medial superior olive

A

Distinguishes interaural delays of 10ms

Accurate sound location

Signal from 1 ear is insufficient to generate an AP - temporal summation needed

Temperotopic organisation

Map of sound source location - rudimentary

Each neuron is sensitive to a specific lag time (fractional head start)

40
Q

Lateral superior olive

A

Interprets differences in intensity of signal from both ears

Direction of sound

41
Q

Tonotopic organisation of SO

A

Different range of frequencies distinguishable

42
Q

Primary auditory cortex

A

Tonotopic organisation

Neurons respond to only very specific frequencies of sound

Cells are responsive to input from both ears

Some are excited by signal from both ears (EE)

Some are excited by 1, inhibited by the other (EI)

Alternating columns

Contrast

Maps different aspects of sound - pitch, loudness, sound localisation, sound duration

43
Q

What do lesions of auditory cortex result in

A

NOT complete deafness

Involvement of subcortical areas in sound perception

Loss of ability to discriminate sound patterns and localise sound

Complete deafness would only result from complete ablation of hair cells or auditory nerve prior to brainstem

Other surrounding cortical areas involved with elaboration of aspects of sound

Parietal - direction, temporal - meaning (sound of someone’s voice etc)

44
Q

Parietal pathway and hearing

A

Direction

45
Q

Temporal pathway and hearing

A

Meaning

46
Q

Wernicke’s area

A

Comprehension of auditory and visual info

IQ test

47
Q

Arcuate fasciculus

A

Connects Wernicke’s area with Broca’s area

Capacity to understand and articulate language

48
Q

Broca’s area

A

Plans & co-ordinates vocalisation

49
Q

Angular gyrus

A

Implicated in some dyslexias

50
Q

Parts of brain associated with language implementation system

A

Frontal - logic - high level of thinking

Parietal - movement (sense)

Temporal - Emotional processing and memory

51
Q

Hemisphere dominant in language

A

Left

52
Q

Right hemisphere is dominant in

A

Spatial/temporal relations

53
Q

Wada procedure

A

One hemisphere is anaesthesised

54
Q

What is epilepsy

A

Excessive electrical activity

Focal region that is source of electrical discharge - can spread and affect the whole brain

Corpus callosum may be severed as treatment to reduce spread

55
Q

Pathway when speaking a heard word

A

Auditory cortex → Wernickes → through arcuate to Brocas → motor cortex

56
Q

Speaking a written word

A

Visual cortex → Angular gyrus → Wernickes → Brocas → motor cortex

57
Q

Broca’s aphasia

A

Laboured slow speech in monotone

Impaired articulation

Comprehension is intact

58
Q

Wernicke’s aphasia

A

Fluent, melodic speech

Errors in word choice

Difficulty in comprehending

59
Q

Conduction aphasia

A

Intelligible simple speech and comprehension

Difficulty repeating sentences

60
Q
A

conductive deafness

61
Q
A

normal hearing

62
Q
A

conductive deafness

63
Q
A

sensorineural deafness

64
Q
A

C

65
Q
A

B

66
Q
A

C

67
Q
A

D

68
Q
A

B

69
Q
A

B

70
Q
A

CNS (36 decks)

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