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PBL SEM 3 > CASE 4 - auditory pathway, vestibular system, otitis media > Flashcards

CASE 4 - auditory pathway, vestibular system, otitis media Flashcards

1
Q

what are the 2 parts of the middle ear?

A
  • tympanic cavity
  • epitympanic recess (superior to tympanic cavity) — lies next to mastoid air cells
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2
Q

what separates the vestibule from the middle ear?

A

oval window

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3
Q

name the 2 perilymph filled chambers

A

scala vestibuli and scala tympani

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4
Q

what is the channel that ends at the round window?

A

scala tympani

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5
Q

what chamber is continuous with the vestibule?

A

scala vestibuli

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6
Q

describe in full the mechanics of hearing from the auricle to a transduction of sound into neural signals

A
  1. the auricle (pinna) collects sound waves and channels them into the external auditory meatus, where sound is amplified
  2. sound causes the tympanic membrane to move — this movement causes vibration of the ossicles = mechanical energy
  3. the stapes is connected to the oval window
  4. sound waves reaching the inner ear travel through the membranous labyrinth of the cochlea, which consists of 3 ducts
  5. when vibration caused by sound reaches the cochlea of the inner ear, periodic displacement of the basilar membrane relative to the tectorial membrane causes bending of stereocilia and depolarises hair cells within the spiral organ of corti
  6. this results in transduction of sound into neural signals
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7
Q

what is the effect of depolarisation due to bending of the sterocilia?

A

increased release of neurotransmitter at the synapses between hair cells and afferent nerve fibres

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8
Q

what happens when the threshold is reached in the afferent nerve fibres (during depolarisations of the hair cells)?

A

action potentials are produced

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9
Q

within regions of the organ of corti, what is the amplitude by which the basilar membrane is repeatedly displaced as it vibrates dependent on?

A

sound frequency

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10
Q

what are the differences in displacement for high and low frequency sounds?

A

high frequency — largest displacement in the basal region of the cochlea

low frequency — largest displacement in the apical region

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11
Q

what is the function of OHCs?

A

= muscular

> tense tectorial membrane (when basilar membrane vibrates with sound)
contract to stiffen the organ of corti and fine tune the frequency of hearing
focuses the resonant frequency of the basilar membrane so you can hear the difference between smaller changes in frequency

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12
Q

what is the function of inner hair cells?

A

= original sensors of sound

  • depolarise (due to movement of K+) when the hair moves 2 angstroms in fluid movement in organ of corti
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13
Q

what causes a higher firing rate of neurons?

A
  • as a stimulus gets more intense, the basilar membrane vibrates with greater amplitude, causing the membrane potential of the activated hair cells to be more depolarised or hyperpolarised
  • as a result, the nerve fibres with which the hair cells synapse fire action potentials at greater rates
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14
Q

how is the number of activated neurons affected?

A
  • more intense stimuli produce movements of the basilar membrnae over a greater distance, which leads to the activation of more hair cells
  • in a single auditory nerve fibre, this increase in the number of activated hair cells causes a broadening of the frequency range to which the fibre responds
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15
Q

where do all ascending auditory pathways converge onto?

A

inferior colliculi

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16
Q

where is the primary auditory cortex?

A

superior temporal gyrus, right under lateral fissure

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17
Q

summarise the auditory pathway

A
  • cochlear nucleus
  • superior olivary nucleus
  • inferior colliculus
  • medial geniculate
  • primary auditory cortex
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18
Q

how does the voice change with conductive vs sensori-neural?

A

conductive — voice stays same loudness
sensori-neural — speak with a noticeably louder voice

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19
Q

what is the most common cause of acquired hearing loss?

A

otitis media with effusion

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20
Q

what is otitis media?

A

an inflammatory condition of the middle ear that results form dysfunction of the eustachian tube as a result of inflammation of the mucous membranes/adenoid tonsils in the nasopharynx

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21
Q

how does a middle ear effusion result?

A
  • because of the eustachian tube dysfunction, the gas volume in the middle ear is trapped and parts of it are slowly absorbed by the surrounding tissues, leading to -ve pressure in the middle ear
  • eventually the -ve middle ear pressure can reach a point where fluid from surrounding tissues is sucked into the middle ear’s cavity, causing a middle-ear effusion
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22
Q

most acute effusions resolve in how long?

A

2-4 weeks

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23
Q

in younger children, what can persistent effusions and decreased hearing be associated with?

A

impairment of language acquisition skills

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24
Q

signs or symptoms of infection in otitis media with effusion?

A

usually none

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25
Q

when does a middle ear infection occur?

A

when the trapped fluid becomes infected by bacteria or virus from the nasopharynx

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26
Q

what is a grommet?

A

aka tympanostomy tube

  • a tube that is inserted into the TM and ventilates the middle ear cavity (takes over eustachian tube function)
  • grommets are extruded from the tympanic membrane as it heals (lasting from 6 months to 2 years)
  • developmental outcomes are not improved by grommet insertions
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27
Q

what is recurrent tonsillitis most commonly caused by in children?

A

group A beta-haemolytic streptococcus pyogenes (GABHS) infections — aka. strep throat

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28
Q

why are children more likely to get recurrent tonsillitis?

A
  • bigger tonsils
  • exposed to more germs
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29
Q

what is the pharyngotympanic tube like in children? effect?

A

more narrow and horizontal — more difficult to drain and easier to get clogged

30
Q

how can gentamicin cause vertigo?

A

destroys the vestibular epithelium — vertigo for around 2 weeks before the body compensates for the lack of vestibular input on that side

31
Q

what is tinnitus?

A
  • the sensation of a sound (ringing/buzzing) when there is no auditory stimulus
  • can occur without hearing loss
  • does usually not have a serious cause but vascular malformation/vascular tumours may be associated
32
Q

what type of hearing loss is caused by an acoustic neuroma?

A

sensory neural (benign tumour of cochlear nerve)

33
Q

what is an automated otoacoustic emission (AOAE) test?

A
  • measures the integrity of the inner ear
  • a small soft-tipped earpiece is placed in the babys ear and gentle clicking sounds are played
  • acoustic energy is produced in response to the clicks and is detected by a microphone within the probe
34
Q

what is an automated auditory brainstem response (AABR) test?

A
  • measures the integrity of the inner ear but also the auditory pathway
  • can therefore detect the rate condition of auditory neuropathy in children who are deaf but have normal otoacoustic emissions (because the cochlea is normal)
  • the stimulus (either clicks or tones) is presented using earphones or an ear canal probe, and the electrophysiological response from the brainstem is detected by scalp electrodes
35
Q

what are test limitations of the neonatal test (AOAE/AABR)?

A

> both require a quiet baby and a quiet environment
debris in the canal or middle ear fluid can affect the tests (including amniotic fluid in the ear canal following birth)
only the AABR test will detect auditory neuropathy (where the cochlea is normal)
neither test will detect central hearing impairment (where hearing loss is secondary to dysfunction pf the pathways from the brainstem to auditory cortex)

36
Q

what is a +ve Rinne’s test and what does it suggest?

A

AC > BC
= either normal or sensori-neural hearing loss

37
Q

what is suggested if BC > AC?

A

conductive hearing loss

38
Q

what is an audiogram a plot of?

A

intensity in dB of hearing threshold vs frequency Hz

39
Q

how are AC (air conduction) thresholds measured?

A
  • determined by presenting the stimulus in air with the use of headphones
  • the patient presses a button when they hear a noise and the quietest sound which a patient can hear is determined
40
Q

what does an air-bone gap indicate?

A

problem somewhere in your outer or middle ears

41
Q

what is tympanometry a test of?

A
  • middle ear compliance
  • tells us how the eardrum moves
  • measures the stiffness of the eardrum and estimates middle ear pressure and the volume of the external canal
42
Q

how is tympanometry carried out?

A
  • a probe is placed in the ear canal
  • sounds play and the changes in air pressure make the eardrum move back and forth
  • measurements of the movement of the eardrum are recorded in a tympanogram
43
Q

small vs. big air bone gap?

A

big = conductive
small = sensorineural

44
Q

describe the caloric test

A
  • this is a test of the vestibule-ocular reflex that involves irrigating cold or warm water into the external auditory canal
  • ice cold or warm water or air is irrigated into the external auditory canal, using a syringe
  • the temp difference between the body and injected water creates a convective current in the endolymph of the nearby horizontal semicircular canal
  • hot and cold water produce currents in the opposite directions and therefore a horizontal nystagmus in opposite directions
  • nystagmus = a rhythmical, repetitive and involuntary movement of the eye
45
Q

COWS - caloric test

A

> COLD water mimics a head turn to the contralateral side
both eyes turn to the same (ipsilateral) ear, with the horizontal nystagmus to the OPPOSITE (contralateral) ear

> WARM water mimics a head turn to the ipsilateral side
both eyes turn to the opposite (contralateral) ear, with the horizontal nystagmus to the SAME (ipsilateral) ear

COLD OPPOSITE WARM SAME

46
Q

how does an intranasal steroid spray treat otitis media with effusion? example?

A
  • eg. beclometasone
  • reduced inflammation in the nose
  • enables the eustachian tube to work better
  • reduce leukocyte infiltration — increases transcription of anti-inflammatory proteins (lipocortin - targets phospholipase A2) and decreases transcription of pro-inflammatory proteins
47
Q

how can enlarged adenoids cause a build up of pressure?

A
  • adenoids are larger in children than they are in adults
  • adenoids are close to eustachian tube — can become obstructed — fluid has no where to go in infection and so pressure builds
48
Q

what is tympanocentesis? when is it carried out?

A

= drainage of fluid from the middle ear usually caused by otitis media, by using a small-gauge needle to puncture the tympanic membrane
- main indication for tympanocentesis is the failed treatment with antibitoic
- immediate improvement in hearing and symptoms of aural fullness and pressure

49
Q

how long do ventilation tubes stay in the ear?

A

4-18 months

50
Q

how long do grommets stay in?

A

6-12 months

51
Q

what is aphasia?

A

= the inability to speak, write or understand the written or spoken word, which results from a lesion in the brain

52
Q

what hemisphere is dominant for language in over 95% of right handers and over 70% of left-handers?

A

left hemisphere

53
Q

the ability to hear a word then repeat it out loud requires transfer of info from Wernicke’s to Broca’s across what?

A

the sylvian fissure

54
Q

what is Brodmann 22 area?

A

primary association area/superior temporal gyrus

55
Q

what is left brodmann 44/45?

A

Broca’s area

56
Q

what does a lesion to Wernicke’s area cause?

A
  • sensory/receptor aphasia
  • fluency of language but words are muddled
57
Q

what does a lesions to Broca’s area cause?

A
  • motor/expressive aphasia
  • reduced speech fluency with relatively preserved comprehension
  • patients know what they want to say, but can’t get the words out
58
Q

what is the name of associated fibres connecting the Wernicke’s area and the Broca’s area?

A

the arcuate fasciculus

59
Q

what is conductive aphasia?

A
  • when there is a lesion to the arcuate fasciculus
  • the output of speech is fluent but paraphrasing, comprehension of spoken word is intact, and repetition is severely impaired
  • naming and writing are also impaired
  • reading aloud is impaired, but reading comprehension is preserved
60
Q

what is global/central aphasia?

A

the combination of expressive problems of Broca’s aphasia and the loss of comprehension of Wernicke’s with loss of both language production and understanding

61
Q

what is dysarthria?

A

motor inability to speak

62
Q

in which aphasia is there poor repetition but comprehension is still intact and speech is fluent?

A

conduction — arcuate fasciculus affected

63
Q

where are broca’s and wernicke’s areas?

A

broca’s = inferior frontal gyrus
wernicke’s = superior temporal gyrus

64
Q

what can speech and language therapy help with?

A

> understanding what is being said to them
listening and following instructions
using words
joining words together in sentences
saying sounds and speaking clearly
eating and drinking
communicating and interacting with other children
understanding their environment

65
Q

which otolith organ detects horizontal acceleration?

A

utricle

66
Q

where does signal transduction occur in the vestibular system?

A

ampullae

67
Q

deflection towards vs away from kinocilium

A

deflection towards the kinocilium increasing firing, deflection away from the kinocilium decreases it

68
Q

hair cells are the motion receptors of the inner ear, embedded within the walls of what?

A

semicircular canals and otolithic organs

69
Q

the apical lining of the hair cells in the semicircular canals is covered by a gelatinous mass called the ____?

A

cupula

70
Q

the cupula of the utricle and saccule has an additional superficial fibrous layer called the _________ which contains numerous crystals of calcium carbonate called ______?

A
  • otolithic membrane
  • otoconia
71
Q

what is the reason why the rotational movements don’t stimulate the maculae of the otolithic organs?

A

the flow of the endolymph alone is not enough to cause the shearing of the otolithic membrane, thus it never moves the cilia

  • the otolithic membrane in the otolithic organs makes the layer over the hair cells a lot heavier than the cupula in the semicircular canal

PBL SEM 3 (49 decks)

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