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Year 2 - BRS > 2.10 - Auditory and vestibular systems > Flashcards

2.10 - Auditory and vestibular systems Flashcards

1
Q

What does the vestibular organ (canals) do?

A

Captures low frequency motion (movements)

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2
Q

What does the hearing organ (cochlea) do?

A

Captures high frequency motion (sound)

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3
Q

What is frequency/pitch (Hz)?

A

Cycles per second, perceived tone

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4
Q

What is amplitude/loudness (dB)?

A

Sound pressure, subjective attribute correlated with physical strength

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5
Q

What is the human range of hearing in terms of frequency and loudness?

A
  • frequency: 20-20000 Hz
  • loudness: 0-120 dB sound pressure level (SPL)
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6
Q

What three sections are the ear divided into?

A
  • outer ear
  • middle ear
  • inner ear
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7
Q

What is found in the outer ear?

A
  • auricle (pinna)
  • external auditory meatus
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8
Q

What is found in the middle ear?

A
  • ossicles: malleus, incus, stapes
  • tympanic membrane (eardrum) and cavity
  • stapedius muscle
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9
Q

What is found in the inner ear?

A
  • cochlea
  • semicircular canals
  • vestibular nerve
  • cochlear nerve
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10
Q

What are the functions of the outer ear?

A
  • to capture sound and to focus it to the tympanic membrane
  • modest amplification (10dB) of upper range of speech frequencies by resonance in the canal
  • to protect the ear from external threats (by hairs and wax)
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11
Q

What is the main function of the middle ear?

A

Mechanical amplification (can provide an additional 20-30 dB)

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12
Q

What is the hearing part of the inner ear?

A

Cochlea

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13
Q

What is the function of the inner ear (cochlea)?

A
  • transduce vibration into nervous impulses
  • it does so in a way that captures the frequency (pitch) and intensity (loudness) of the sound
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14
Q

What three components is the cochlea divided into and describe them?

A
  • scala vestibuli, scala media and scala tympani
  • scala vestibuli and scala tympani - bone structures, contain perilymph (high in sodium)
  • scala media - membranous structure, contains endolymph (high in potassium)
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15
Q

What is located in the scala media of the cochlea?

A

The hearing organ (Organ of Corti), which lies in the basilar membrane

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16
Q

How is the basilar membrane arranged?

A

Tonotopically, using the same principle as a xylophone (base is narrow and tight, detecting high frequencies; apex is wide and loose, detecting low frequencies)

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17
Q

What two kinds of hair cells does the organ of Corti contain?

A
  • inner hair cells (IHC)
  • outer hair cells (OHC)
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18
Q

What would happen to high frequency vs low frequency sounds in the basilar membrane?

A
  • high frequency sounds = thicker base moving more than apex = cells in base will be participating more in transduction of sound
  • low frequency sounds = thinner apex moving more than base = cells in apex will be participating more in transduction of sound
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19
Q

What is the tectorial membrane?

A

Located above the hair cells (organ of Corti) and allows hair deflection, which in turn will depolarise the cell

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20
Q

What is the function of inner hair cells (organ of Corti)?

A
  • carry 95% of the afferent information of the auditory nerve
  • their function is the transduction of the sound into nerve impulses
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21
Q

What is the function of the outer hair cells (organ of Corti)?

A
  • carry 95% of the efferents of the auditory nerve
  • function is modulation of the sensitivity of the response
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22
Q

What are the stereocilia?

A

Hairs of the hair cells

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23
Q

How does transduction of sound work?

A
  • inner hair cells
  • the deflection of the stereocilia towards the longest cilium (kinocilium) will open K+ channels
  • this depolarises the cell, releasing the neurotransmitter (glutamate released as Ca2+ enters) to the afferent nerve which then depolarises
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24
Q

What will higher amplitudes of sound do to the transduction process?

A

Higher amplitudes (louder) will cause greater deflection of stereocilia towards kinocilium in inner hair cell, and K+ channel opening

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25
Q

What is the difference between depolarisation and hyper-polarisation during transduction?

A
  • depolarisation opens K+ channels
  • hyper-polarisation closes K+ channels
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26
Q

What is the overall pathway for sound through the ear (until the cochlea)?

A

signal (sound) –> outer ear (moderate amplification) –> external auditory meatus –> tympanic window –> reverberates against 3 ossicles (middle ear) –> oval window (from stapes) amplifies further –> cochlea (liquid) –> scala vestibular –> scala media –> scala tympani (sheer force causes hair cells to move) –> K+ in, Ca2+ in, GLUT out –> neuronal signal

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27
Q

What three mediums do sound travel through during the process?

A

Air –> bone (middle ear) –> liquid (inner ear)

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28
Q

What is the auditory nerve pathway like after the cochlea?

A
  • spiral ganglions from each cochlea project via the vestibulocochlear nerve (CN VIII) to the ipsilateral cochlear nuclei (monoaural neurons) in the brainstem (pons)
  • auditory information crosses at the superior olive level (brainstem)
  • after this point, all connections are bilateral (combination of L + R hearing)
  • superior olive (BS) –> inferior colliculus (BS) –> medial geniculate body (thalamus) –> auditory cortex
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29
Q

A lesion where in the auditory nerve pathway causes unilateral hearing loss?

A

Lesion between cochlear nucleus and superior olive (as superior olive is where information becomes bilateral)

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30
Q

What are two ways to classify hearing loss by?

A
  • anatomical - conductive hearing loss, sensorineural hearing loss, central hearing loss
  • timing - sudden / progressive
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31
Q

What is conductive hearing loss?

A

Problem is located in outer or middle ear (cells working fine, problem with sound getting into ear)

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32
Q

What is sensorineural hearing loss?

A

Problem is located in the inner ear - sensory organ (cochlear) or auditory nerve –> 90% of all hearing loss

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33
Q

What is central hearing loss?

A

Very rare and originates in the brain and brainstem - affects both conduction and transduction of sound and affects more than one part of the ear

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34
Q

How can hearing loss be classified in terms of timing?

A
  • sudden hearing loss - minutes to days
  • progressive hearing loss - months to years
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35
Q

What are the causes of conductive hearing loss in the outer ear?

A
  • wax
  • foreign body
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36
Q

What are the causes of conductive hearing loss in the middle ear?

A
  • otitis (inflammation, liquid in middle ear)
  • otosclerosis (extra bone produced causing hearing loss)
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37
Q

What are the causes of sensorineural hearing loss in the inner ear?

A
  • noise
  • presbycusis - normal hearing loss due to loss of hairs as you get old
  • ototoxicity - exposure to meds/drugs can be toxic
38
Q

What are the causes of sensorineural hearing loss in the auditory nerve?

A

Acoustic neuroma (vestibular schwannoma) (unilateral) - pushes CN VIII

39
Q

How can you quickly test someone’s hearing as part of a clinical assessment?

A

Whisper in ipsilateral ear whilst rubbing fingers in contralateral ear

40
Q

What is the tuning fork used for?

A
  • two tests assess the presence of gross hearing loss
  • used to compare hearing on both sides and see if issue is in outer/inner ear
  • Weber test - sensorineural hearing loss - tap ringing fork on head, sound should be in middle
  • Rinne test - conductive hearing loss - sound through mastoid should not be as loud as sound in ear (reduced conduction through air e.g. due to wax would impact this)
41
Q

What is an audiogram?

A
  • where the hearing thresholds are plotted to define if there is a hearing loss or not
  • normal hearing threshold is located between 0-20 dB
42
Q

What are the degrees of hearing loss based on where the hearing thresholds are located?

A
  • normal hearing: 0-20dB
  • mild hearing loss: 20-40dB
  • moderate hearing loss: 40-70dB
  • severe hearing loss: 70-90dB
  • profound hearing loss: 90-130dB
43
Q

What does the audiograph for conductive hearing loss look like?

A
  • air conduction impaired - line shifted lower on graph (lower hearing level)
  • bone conduction normal
44
Q

What does the audiograph for sensorineural hearing loss look like?

A

Both air and bone conduction lines are together and are lower down

45
Q

What are otoacoustic emissions (OAEs)?

A
  • the normal cochlea produces low-intensity sounds called OAEs
  • these sounds are produced specifically by outer hair cells as they expand and contract
  • this test often part of the newborn hearing screening and hearing loss monitoring
46
Q

What are the treatments for hearing loss?

A
  • underlying cause e.g. earwax, infection
  • hearing aids - amplify sounds and different frequencies
  • cochlear implants - replaces function of hair cells in transduction
  • brainstem implants - risky and rare
47
Q

What are the inputs of the vestibular system?

A

Movement and gravity via mechanical sensors (canals and otoliths)

48
Q

What are the outputs of the vestibular system?

A

Perception and reflexes that maintain posture and gaze - ocular reflex and postural control

49
Q

What is the role of the CNS in the vestibular system?

A

Integrates information from inputs and generates the output responses

50
Q

Where is the vestibular organ?

A
  • posterior area of inner ear
  • inner ear contains hair cells for hearing and balance
51
Q

What parts is the vestibular organ split into?

A
  • vestibule (containing utricle and sacule - otolith)
  • semicircular canals
52
Q

What is in the vestibule?

A
  • utricle and saccule (otolith) are located in the vestibule
  • joined by a conduit
  • saccule is also joined to the cochlea, utricle also joined to semicircular canals
53
Q

What are the semicircular canals?

A
  • there are three semicircular canals on each ear - anterior, posterior, lateral (6 total)
  • semicircular canals have an ampulla on one side, and are connected to the utricle
54
Q

What are otolith organs?

And describe their structure in terms of hair cells.

A
  • utricle and saccule are the otolith organs
  • their hair cells are located on the maculae - gelatinous matrix with otoliths on top
  • the maculae are placed horizontally in the utricle and vertically in the saccule
55
Q

Why are they called otolith organs?

A

They have carbonate crystals on top of the hair cells that help with the movement (deflection) of the hairs

56
Q

What kind of movement do the otolith organs deal with?

A

Linear acceleration and tilt

57
Q

What happens to the otolith organs when upright?

A

The otoliths have a resting potential so the head and neck muscles are contracted/relaxed to keep head in that position

58
Q

What happens to the otolith organs when accelerating/tilting head?

A

Otoliths read the movement and allow for compensatory movements e.g. if head is tilting back, we can snap it forward

59
Q

What kind of movement is the utricle and saccule responsible for sensing?

A
  • utricle - horizontal movement (horizontal maculae, vertical hairs)
  • saccule - vertical movement (vertical maculae, horizontal hairs)
60
Q

Where are the hair cells in the semicircular canals located?

A
  • hair cells in the canals are located in the ampulla
  • ampulla has crista, where the hair cells are located
  • hair cells surrounded by cupula which helps with the hair cell movement
  • rest of the canal only has liquid high in potassium (endolymph)
61
Q

What are the hair cells in the semicircular canals surrounded by?

A

The cupula - a gelatinous substance which the endolymph moves to help with hair cell movement

62
Q

What kind of movement do the semicircular canals deal with?

A
  • angular acceleration
  • cupula moves and displaces hair cells
  • one side of the vestibular system reports depolarisation and the other reports hyperpolarisation
  • information –> brainstem –> integration = which direction head is moving and the acceleration
63
Q

What are the planes of the semicircular canals?

A
  • the orientation of the canals in the head defines three planes
  • anterior and posterior canals form a 90 degree angle
  • lateral canals are horizontal to the other canals
  • therefore they work in pairs
64
Q

What are the pairs that the semicircular canals work in?

A
  • both lateral canals
  • anterior one side and posterior other side and vice versa
65
Q

What do vestibular hair cells have coming off them?

A
  • stereocilia
  • a kinocilium (biggest cilium)
66
Q

What do the cilia coming off vestibular hair cells do?

A
  • allow cells to depolarise with movement of the endolymph, generated by head movement
  • movement of stereocilia towards kinocilium = depolarisation
  • movement of stereocilia away from kinocilium = hyperpolarisation
67
Q

What are hair cell potentials in the vestibular organ?

A
  • hair cells have a resting potential which has a basal discharge to the nerve (posture upright when not moving)
  • hairs moving towards the kinocilium generates depolarisation and an increase in nerve discharge (excitation)
  • hairs moving away from kinocilium generates hyperpolarisation and a reduction in nerve discharge (inhibition e.g. if one ear is being depolarised, the other one is hyperpolarised)
68
Q

What is the nerve path from the vestibular nerve to the brain?

A
  • primary afferents end in vestibular nuclei in the brainstem (pons)
  • vestibular nuclei are main generators of vestibular reflexes
69
Q

What are the main three functions of the vestibular system?

A
  • to detect and inform about head movements
  • to keep images fixed in the retina during head movements
  • balance
70
Q

What are two vestibular reflexes?

A
  • vestibulo-ocular reflex (VOR)
  • vestibulo-spinal reflex (VSR)
71
Q

What does the vestibulo-ocular reflex do?

A
  • keeps images fixed in retina
  • connection between vestibular nuclei and oculomotor nuclei
  • eye movement in opposite direction to head movement with the same velocity and amplitude
  • e.g. staring at dot and moving head but dot stays fixed in eyesight
72
Q

What is the pathway for the vestibulo-ocular reflex?

A

Vestibular organ detects movement –> vestibular nerve –> vestibular nucleus –> abducens nucleus (contralateral) –> via medial longitudinal fasciculus –> oculomotor nucleus (back to other side) –> eye movement (think in terms of direction e.g. move head right means both eyes need to move left, so respective LR and MR contraction)

73
Q

How do we classify vestibular disorders?

A
  • timing and laterality
  • location
  • timing (evolution)
74
Q

What are the main complaints in acute and unilateral vestibular disorder?

A
  • imbalance
  • dizziness
  • vertigo
  • nausea
75
Q

What are the main complaints in slow AND unilateral, or any bilateral loss?

A
  • imbalance
  • nausea
  • NO VERTIGO
76
Q

What are some peripheral vestibular disorders (vestibular organ and/or CN VIII)?

A
  • vestibular neuritis (acute)
  • benign paroxysmal positional vertigo - BPPV (intermittent)
  • Meniere’s disease (recurrent)
77
Q

What are some central vestibular disorders (CNS)?

A
  • stroke (acute)
  • multiple sclerosis (progressive)
  • tumours (progressive)
78
Q

What are acute balance disorders?

A
  • vestibular neuritis
  • stroke
79
Q

What are intermittent balance disorders?

A

Benign paroxysmal positional vertigo (BPPV)

80
Q

What are recurrent balance disorders?

A
  • migraine
  • (Meniere’s disease)
81
Q

What are progressive balance disorders?

A
  • schwannoma vestibular (VIIIth nerve)
  • degenerative conditions (MS)
82
Q

What are the main diagnoses?

A
  • BPPV
  • vestibular neuritis
  • vestibular migraine
  • stroke (cerebellar)
83
Q

What is tested in the core exam?

A
  • eyes
  • ears
  • legs
84
Q

What are some red flag symptoms of vestibular disease? (5)

A
  • headache
  • gait problems
  • hyper-acute onset
  • hearing loss
  • prolonged symptoms (>4 days)
85
Q

How do you test your VOR?

A
  • fast movements of head hard to compensate for vs slow
  • hold head, move fast suddenly and see whether eyes stay fixed
  • if you move left, left horizontal canal responsible
  • e.g. if issue in left canal, if you look right VOR normal but if you look left the eye will not stay fixed initially
86
Q

What is the HINTS exam used for?

A
  • clinical exam in acute dizziness
  • vestibular neuritis (peripheral) or stroke (CNS)?
87
Q

What does the HINTS exam include?

A
  • Head Impulse test - horizontal rotational VOR
  • Nystagmus - vestibular organ vs cerebellar/BS nystagmus
  • Test of Skew deviation - vertical misalignment, usually absent in peripheral pathology (vestibular neuritis)
88
Q

What is benign paroxysmal positional vertigo (BPPV)?

A
  • peripheral disorder where otoliths from the utricle detach from maculae and float around the semicircular canals
  • floating otoliths induce a bigger endolymph flow when the head moves (crystals carry more liquid)
  • movement of head processed by the brain as bigger and faster than in reality
89
Q

What is the nature of BPPV attacks?

A
  • intermittent vertigo attacks every time the head moves quickly, especially when lying down or standing up
  • attacks are short as they end when the endolymph settles
  • when head is still, usually no vertigo symptoms (but some feel unstable/lightheaded when walking)
90
Q

How is BPPV treated?

A

Disorder continues until crystals are taken back to the utricle with repositioning manoeuvres e.g. Epley or Semont

91
Q

Does BPPV cause hearing problems?

A

No - only affects semicircular canals where crystals are floating around (but hearing loss can occur if they have a different condition coexisting e.g. presbycusis)

Year 2 - BRS (84 decks)

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