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auditory & vestibular system Flashcards

1
Q

What are the 3 sections of the ear?

A

Outer, middle, inner ear

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2
Q

What is the outer ear formed by? What are its functions?

A
  • Outer ear formed by pinna & external auditory canal which end up at tympanic membrane (middle ear).
  • Functions:
    1. capture sound & focus it on tympanic membrane
    2. amplify some frequencies by resonance in canal
    3. protect ear from external threats - mechanically by hair to catch element and chemically with pH to neutralise threat
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3
Q

What is the middle ear formed by and what happens there (mechanism)?

A
  • Middle ear starts at tympanic membrane & has 3 ossicles, muscles, ligaments, joints.
  • Ossicles articulate with each other allowing transmission of sound into inner ear via oval window.
  • Wave causes vibration of tympanic membrane which transmits vibration to ossicles causing amplification.
    1. vibrations of large tympanic membrane focuses on smaller window (oval window) so due to larger pressure sound amplified
    2. leverage function of incus-stapes joint increases force on oval window.
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4
Q

What is the hearing part of the inner ear? What happens in the inner ear?

A
  • hearing part is cochlea.
  • Function to transduce vibration of sound into nervous impulses, and to produce frequency (pitch) and loudness (amplitude) analysis of sound.
  • Movement of cells in cochlea differs with pitch and amplitude
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5
Q

When the cochlea is uncoiled what are its compartments and what does each contain?

A
  • Oval window at upper scala vestibuli, round window at lower scala tympani.
  • Scala vestibuli & tympani are continous and share perilymph (high in sodium).
  • Scala media is membranous structure in between the other 2 and contains endolymph (high in potassium).
  • Hearing organ (organ of corti) is in scala media
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6
Q

What lies within the basilar membrane? How is it organised?

A
  • Basilar membrane is membrane of scala media.
  • It contains the organ of corti.
  • Basilar membrane is tonotopically organised
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7
Q

What is the structure of the basilar membrane and its function?

A
  • Has base and apex.
  • Base is narrow and tight and apex is wide and loose.
  • High frequency causes vibration of membrane at higher amplitude towards base of membrane, lower frequency has higher amplitude at apex.
  • Cells in one area for high frequency and the other for low freqeuncy. So organ tonotopically arranged like xylophone (sensitve to different frequencies at different points)
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8
Q

What types of hair cells does the organ of corti contain? What are their structures?

A

Outer hair cells, inner hair cells.

  • Inner hair cells big and round, outer hair cells thin and long
  • inner organised in 1 column, outer in 3 columns.
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9
Q

What causes deflection of the hairs and what does this cause?

A

vibration of sound displaces basilar membrane, cells stimulated, tectorial membrane causes deflection of the hairs, causing depolarisation of the cells

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10
Q

What is the outer hair cells in contact with constantly and why

A

-OHC in constant contact with tectorial membrane bringing membrane closer to IHC or not.

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11
Q

What do IHC carry and what do OHC carry? What is the function of each?

A
  • IHC carry most of afferent info to auditory nerve in order to transduce sound into nerve impulses.
  • OTC carry most of efferents of auditory nerve to modulate sensitivity of response (active amplifier)
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12
Q

How does OHC contribute to transduction?

A
  • OHC can contract to change length to make tectorial membrane come closer to IHC so that IHC can transduce sound.
  • If OHC keeps tectorial membrane away from IHC wont be able to transduce sound
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13
Q

What are the hair of hair cells called? What do they do?

A

Stereocilia.

  • Deflection of stereocilia towards longest cilium will open potassium channels causing depolarisation of cell & liberating neurotransmitter (usually glutamate) so impulse transmitted to CNS.
  • Potassium in endolymph high so available for depolarisation.
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14
Q

What happens when we have a higher amplitude sound (louder sound)?

A

-High amplitude (louder sound) causing more vibration, more movement of basilar membrane, more cells receive movement, more touching of tectorial membrane to IHC, greater deflection of stereocilia, more potassium channels open, greater sensation of loudness.

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15
Q

In transduction how do the OHC compensate for very loud or very soft sounds?

A
  • If sound too soft OHC will contract to bring tectorial membrane closer to IHC so we can hear sound.
  • If too loud OHC can elongate to push tectorial membrane away from IHC so we don’t feel discomfort
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16
Q

What would happen if OHC were damaged?

A

Only be able to hear narrow loudness range. Would not be able to hear very soft sounds, and would hear loud sounds too loudly.

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17
Q

After transduction in the cochlea where does sound go?

A
  • After cochlea goes to cochlear nerve and up to cochlear nucleus (where it can cross to contralateral superior olive or ipsilateral superior olive - more go contralateral), and from superior olive to inferior colliculus (brainstem), medial geniculate body (thalamus) to auditory cortex in temporal lobe.
  • Auditory cortex recognises sound and will connect to language centres to understand it. Brainstem has part in processing sound
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18
Q

How are the nerve fibres arranged and why?

A

Tonotopically.

-Base nerve fibres will transmit only high frequency and apex only low frequency, useful to understand speech

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19
Q

What is frequency? What is the human range of hearing frequency wise? What is the useful range of hearing? When does this decrease?

A
  • Frequency is cycles per second of the wave (hz).
  • Human range is 20-20,000 hz.
  • Useful range is up to 100/150 - 4000Hz.
  • Lose frequency as we age. Then progresses to medium/low frequencies
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20
Q

What is amplitude? What is the human range of hearing amplitude wise? What scale and why?

A
  • Amplitude is loudness (sound pressure/physical strength) in dB.
  • Human range is 0dB-120dB.
  • Decibel scale (log scale) useful because range of sensitivities is very large
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21
Q

Why is a tuning fork used? What are the tests used & their purpose?

A
  • Establish presence/absence of hearing loss with significant conductive component.
  • Weber test - vibrate fork to see if hearing loss symmetric/asymmetric.
  • Rinne test: see if problem is in outer or middle ear
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22
Q

What is pure-tone audiometry (PTA), what does it use and what does it measure? How do you interpret results?

A
  • Measures hearing acuity for different sound intensities and frequency.
  • Uses audiometer that produces sound at varying intensity and frequency and plots threshold on audiogram, minimum volume (loudness) to hear each tone is graphed.
  • Normal hearing threshold 0-20dB, if hearing loss will be outside this range.
  • Can differ between air conduction and bone conduction to see if problem is in outer or middle ear
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23
Q

What is the central processing assessment and what does it measure?

A

-assesses hearing abilities other than detection (discriminate verbal, non-verbal speech), sound localisation, speech in noise etc

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24
Q

What is tympanometry and what does it measure?

A

-Tests conditions of middle ear & mobility of tympanic membrane and conduction of bones by creating variations in air pressure in ear canal (to see how easily air goes to middle ear - anything below normal is resistance - less air going in)

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25
Q

What is otoacoustic emissions OAEs and when is it measured?

A
  • Low-intensity sounds produced by cochlea as Outer Hair Cells contract.
  • Part of newborn hearing screening test & hearing loss monitoring (to see if OHC still working)
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26
Q

What are auditory evoked potentials and how are they measured and evoked?

A
  • Potentials generated by auditory stimuli measured by EEG, electrical activity from cochlea & 8th nerve.
  • Evoked by clicks or tone burst
27
Q

What is auditory brainstem response ARB, how is it measured and evoked?

A
  • Electrical activity from 8th nerve and brainstem nuclei & tracts.
  • Evoked by click
28
Q

What are later responses mainly associated with and what are they evoked by?

A
  • Primary auditory and association cortex

- evoked by tone burst and oddball paradigm

29
Q

What is ABR used for? Advantages?

A
  • ABR used in clinic to see electrical responses from auditory pathway.
  • Does not require attention from patient, can see alterations in latency of waves to point to location of deficit.
  • Wave 1: auditory nerve, wave 3: cochlear nuclear, wave 5 superior olive.
  • Used in babies and children commonly
30
Q

When can cortical potentials be affected?

A

Neurological conditions/processing conditions

31
Q

What are the types of hearing loss and what could be affected?

A
  1. conductive hearing loss: problem in outer or middle ear (problem with conduction of sound)
  2. sensorineural hearing loss; problem in inner ear or auditory nerve (not transmitting sound)
  3. mixed hearing loss: conduction & transduction affected, problem affects more than 1 area of ear
32
Q

In each type of hearing loss what would you see in audiometry?

A
  1. conductive: with air conduction would not hear well (outside threshold) but with bone conduction fine (goes directly in ear)
  2. sensorineural: problem with inner ear so outside threshold generally
  3. mixed: both outside threshold but improvement after bone conduction
33
Q

What are causes of conductive hearing loss?

A
  • Outer ear: wax, foreign body.

- Middle ear: otitis (infection), otosclerosis

34
Q

What are causes of sensorineural hearing loss?

A
  • Inner ear: presbycusis (loss with age), ototoxicity (medication, drugs).
  • Nerve: 8th nerve tumour
35
Q

hat do hearing aids do and what to they require?

A

Amplifies sound making it louder. Needs preservation of cells

36
Q

What do cochlear implants do and what do they require?

A
  • Replaces function of hair cells by receiving sound, analysing it and transforming it into nerve impulse sending it to auditory nerve.
  • Needs functioning auditory nerve
37
Q

What is a brainstem implant? Risk? When is it used?

A
  • Sends electrical signals directly to brainstem (electrode in brainstem).
  • Risky surgery, unpredictable effects.
  • Only for bilateral auditory nerve damage when there are no other options
38
Q

What are the inputs, outputs of the vestibular system? What integrates this information and generates the responses?

A
  • Inputs: visual information , proprioceptive information, vestibular information.
  • Outputs: mainly reflexes to for posture & gaze.
  • CNS integrates this information and generates the responses
39
Q

Where is the vestibular organ located? What is its structure?

A
  • In posterior area of inner near, in temporal bone.
  • Has hair cells for hearing and balance.
  • Posterior part has vestibule formed by utricle & saccule which are joined by conduit. They have liquid.
  • 3 semi-circular canals (posterior, anterior, lateral) which have ampulla on one side. Connected to utricle (fluid goes around utricle and canals)
40
Q

What do anterior and posterior semi-circular canals form and what does this determine?

A

-Anterior & posterior semi-circular canals form 90 degree angle between them giving us planes which determine which structure will be stimulated with specific head movement

41
Q

What do vestibular hair cells have? What happens when the head moves? Where are these hair cells

A
  • Vestibular hair cells have kinocillium (biggest cillium) & stereocilia (orientated to one side).
  • When head moves endolymph in inner ear moves and depending on if stereocillia move towards of away of kinocilium we get depolarisaiton or not.
  • Bigger movement generates bigger response. Hair cells in all 5 vestibular structures
42
Q

What are the otolith organs? What do they contain/structure? How do these things contribute?

A
  • Otolith organs are utricle & saccule.
  • They have hair cells on maculae (horizontally in utricle, vertically in sacule), above hair cells is gelatinous matrix and otolith (crystals) that help movement of hairs.
  • When head moves in specific direction otoliths help weigh it more to one direction helping cilia deflect
43
Q

Do semi-circular canals have otoliths?

A

no, only in pathology

44
Q

What is the structure of the semi-circular canals and why?

A
  • In ampulla there are ampullary crista.
  • Hair of hair cells covered with something less dense than gelatin (cupula).
  • When endolymph comes and goes it moves cupula to one direction helping cell deflection
45
Q

How are the semi-circular canal planes orientated?

A
  • Anterior and posterior have 90 degree angle, with left and right anterior and posterior being in the same plane.
  • Lateral planes orientated horizontal to other canals
46
Q

Where do primary afferents end up? What generates the reflexes? Where else does this information project from there and why?

A
  • Primary afferents end up in vestibular nuclei and in cerebellum.
  • Information goes up to cerebellum for coordination & feedback but vestibular nuclei in brainstem are main generator of reflexes.
  • From there information projects to spinal cord for postural changes and extra-ocular muscle nuclei for eye movements, cerebellum for feedback and centres of CV and respiratory control
47
Q

What types of vestibular reflexes do we have?

A

Vestibulo-spinal, vestibulo-cerebellar, vestibulo-ocular reflex

48
Q

What does the vestibular cortex do? Which area is most active?

A
  • vestibular cortex has inputs and integrates information.

- Uses many cortical areas but mostly parieto-insular vestibular cortex (PIVC) in parietal lobe

49
Q

What are the functions of the vestibular system?

A
  1. detect & inform about head movements
  2. keep images fixes in retina during head movements
  3. postual control
50
Q

what are the 3 potentials of the hair cells and why? What causes them?

A
  1. resting potential - basal discharge causes firing (eg gravity need to stay upright)
  2. depolarisation - when head moved - increased discharge & neuronal firing. When one side depolarizes other is inhibited. movement of steroecilia towards kinocilium causes depolarisation and vice versa hyperpolarisation
  3. inhibition - hyperpolarisation (movement of stereocilia away from kinocilium)
51
Q

How do otolith organs respond to head movement?

A
  • Work with linear acceleration (movement in horizontal/vertical plane) and tilt (back/forward), when upright basal discharge.
  • Utricle sensitive to horizontal movement, sacule to vertical movement.
  • Head tilt allows muscle of head or neck to compensate to avoid falls
52
Q

how do semi-circular canals respond to head movement? What is the output signal? What would rotating head stimulate?

A
  • Respond to angular acceleration.
  • Movement towards anterior right stimulates canal in that direction.
  • Moving head moves endolymph, pushes cupula, displaces cells causing either depolarisaiton or hyperpolarsation depending on side - integrated in brainstem.
  • Output signal of vestibulocochlear nerve is velocity.
  • Rotating head stimulates horizontal semicircular canals (yes/no movement)
53
Q

How do canals work in pairs?

A
  • Both lateral planes work together (when one stimulated, other inhibited).
  • Anterior from one side works with posterior from other side.
54
Q

What is purpose of vestibulo-ocular reflex? How quick is it? What is the mechanism?

A
  • Allows us to keep image fixed in retina despite head movement.
  • Quickest reflex.
  • Connection between vestibular nuclei & oculomotor nuclei allows eye to move in opposite direction of head movement but same velocity & amplitude
55
Q

What is purpose of vestibulo-spinal reflex ? What is the mechanism?

A
  • When walking and losing balance.
  • Connection between vestibular nuclei and spinal cord so motor neurones can connect with limb muscles (lateral tract) and neck & back muscles (medial tract) for postural control, avoid falls, and compensatory body movement according to head position
56
Q

What are the different vestibular tests? What happens?

A
  1. caloric test (stimulates inner ear with different temperatures to generate response - normally nystagmus)
  2. video head impulse test (VHIT) - tests both integration -can be normal in those with deficit
  3. vestibular evoked myogenic potential (VEMP) -tests connection between vestibular system and neck muscles to see response (if absent doesn’t necessarily mean abnormal)
  4. rotational test (make them turn to one direction to generate response)
57
Q

How do you assess posture & gait, eye movement, cerebellar function, brains stem function?

A
  • Posture and gait with posturography, questionairres.
  • Eye movements (record movements)
  • cerebellar function (neurological test)
  • brain stem (CNS investigation, CT/MRI)
58
Q

What is balance disorder? What are symptoms? What is vertigo & dizziness? Categorised based on?

A

-Dizziness and vertigo.
-Vertigo: perception of things spinning.
Dizziness - vague.need to specify
- Categorised based on location of affected structure and evolution of signs and symptoms

59
Q

What are some peripheral vestibular disorders?

A

Vestibular neuritis, BPPV, menier’s disease, unilateral and bilateral vestibular hypofunction. (Before brainstem.)

60
Q

What is vestibular neuritis?

A

Inflammation of vestibular nerve. acute

61
Q

What is BPPV (benign paroxysmal positional vertigo)? What happens?

A
  • Crystals floating around go to canals and make movement bigger than what is it.
  • Only affected when head is moving
  • intermittent
62
Q

What is meniere’s disease? What happens?

A
  • Affecting hearing and balance, problem with absorption of endolymph, increased amount of liquid in inner ear breaks membranes causing intoxication of cells.
  • Recurrent because membrane breaks down, regenerates, breaks done again
63
Q

What are some central vestibular disorders?

A

Stroke, MS, tumours (shwannoma vestibular tumour on vestibular nerves)

64
Q

What are other causes of dizziness?

A

Heart disorder, anaemia, pre-syncopal episode, orthostatic hypotension, hypoglycaemia, psychological, gait disorders

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