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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
Unfurled cochlea (2 and 3/4 turns)
Sound frequencies seem to affect basilar membrane at different optimised places
26
How is frequency sensed Range of freq heard by young vs old
Mainly by "place principle" Young: 20-20,000 Hz Old: 50-5,000 Hz
27
How is loudness sensed
By amplitude of response Spatial summation Activation of outer hair cells - some signal to brain
28
Low freq
Maximal vibration at tip (helicotrema)
29
High freq
Closer to base
30
Place principle
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
Deafness Different types
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
MOA of hearing aid
* Under mastoid process is fluid filled inner ear - cochlear is there * Sit it on mastoid process - amplifies signal
33
What do hearing tests examine
Air conduction - outer, middle, inner ear and auditory pathway function Bone conduction - bypasses the outer and middle ear Tuning fork tests & audiometry
34
Pure tone audiogram
35
Deafness severity
36
Neural processing within auditory pathway
Inner hair cells synapse on \> 90% of ganglion cells - Glu NT Eighth CN - vestibulocochlear Signal has phasic and tonic components
37
Overview of auditory pathway
38
How do fibres travel in the auditory pathway
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
Medial superior olive
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
Lateral superior olive
Interprets differences in intensity of signal from both ears Direction of sound
41
Tonotopic organisation of SO
Different range of frequencies distinguishable
42
Primary auditory cortex
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
What do lesions of auditory cortex result in
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
Parietal pathway and hearing
Direction
45
Temporal pathway and hearing
Meaning
46
Wernicke's area
Comprehension of auditory and visual info IQ test
47
Arcuate fasciculus
Connects Wernicke's area with Broca's area Capacity to understand and articulate language
48
Broca's area
Plans & co-ordinates vocalisation
49
Angular gyrus
Implicated in some dyslexias
50
Parts of brain associated with language implementation system
Frontal - logic - high level of thinking Parietal - movement (sense) Temporal - Emotional processing and memory
51
Hemisphere dominant in language
Left
52
Right hemisphere is dominant in
Spatial/temporal relations
53
Wada procedure
One hemisphere is anaesthesised
54
What is epilepsy
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
Pathway when speaking a heard word
Auditory cortex → Wernickes → through arcuate to Brocas → motor cortex
56
Speaking a written word
Visual cortex → Angular gyrus → Wernickes → Brocas → motor cortex
57
Broca's aphasia
Laboured slow speech in monotone Impaired articulation Comprehension is intact
58
Wernicke's aphasia
Fluent, melodic speech Errors in word choice Difficulty in comprehending
59
Conduction aphasia
Intelligible simple speech and comprehension Difficulty repeating sentences
60
conductive deafness
61
normal hearing
62
conductive deafness
63
sensorineural deafness
64
C
65
B
66
C
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D
68
B
69
B
70

CNS (36 decks)

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