Week 6 Vestibular System

Question 1

Hyperacusis

Answer 1

o Increased sensitivity and responsivity to environmental sounds
o Can be frequency specific or broadband
o Presentations can vary, symptoms include
 Intolerance to certain sounds
 Pain in the ear, +/- cephalic pain – headache in response to sound
 Distress, anxiety, startle, phonophobia (fear of sound), social isolation
 Emotive responses
 Avoid going places you know will be loud
o Aetiology can vary, with abnormalities reported in:
 Hair cell functioning
 CNVIII efferent functioning – more efferents mean finer processing
 A1 auditory processing
 Ventral stream parabelt processing
 Vestibular processing
o Tiny things can be aggravating
 Clocks, chewing, breathing, typing

Question 2

Misophonia

Answer 2

o Increased emotional responsivity to a certain trigger set of sounds
o A type of hyperacusis
o Presentations are largely emotive
 Intolerance to the trigger set: frustration - anxiety - rage
 Also physiological stress responses e.g. nausea, TMJ, cluster headaches, hypertension
 Social isolation can be pronounced, affecting professional and personal life
o Aetiology ?
 Psychological – traumatic experience?
 Physiological – pattern of acoustic energy causing stress response?
o Treatment
 CBT – recognise the sound makes me feel like this, be aware of sound and channel response into a different emotional response
 Drugs to treat the symptoms that come from the condition itself – still have the responsiveness but have dulled the anxiety
 Not treating the cause
 Avoidance – if the trigger set comes from people then you’re telling them to socially isolate themselves

Question 3

Grommets

the human ear

Answer 3

• Metal loop about 1mm goes into tympanic membrane to treat middle ear infections
• Chronic infection – get pussy, pushes on ear drum, sore, hearing impairment
  o Lose sensitivity
  o Physics of the bones can’t work properly if full of stuff
• Bacteria can go up Eustachian tubes into middle ear
  o For adults our immune system can deal with it
  o In kids the tubes are different shaped – shorter to bacteria travel less distance, and more horizontal so can’t drain as easily, and narrow so get blocked
• A hole for pus to drain out of your ear, and give an opening for air circulation to clear infection
  o Also a pore for antibiotics into middle ear
• Functional recovery of hearing loss even though punctures membrane
  o Membrane can grow back
  o Over time it fuses and pops out the grommet
• Most useful for which type of hearing impairment?
  o Conduction based, sensorineural loss, presbycusis, sociacusis?

Question 4

Vestibular sensation

Answer 4

• Extra sense
  o Don’t realise it is a sensory system until something goes wrong – hidden sense
  o Tells you when your body is in motion
• Vestibular labyrinth extends from cochlea, filled with fluid
• Provides key information on how the body is positioned relative to gravity - sense of balance
  o Has a lot to do with ability to stay upright and stops from tripping

Question 5

Vestibular labyrinth

Answer 5

• 2 otolith organs: utricle and sacculus
  o Linear acceleration + static position
  o Utricle: linear acceleration – forwards or backwards
  o Sacculus: vertical acceleration – up or down
• 3 semi-circular canals
  o Rotational accelerations of head
  o Circular canals – rotation of the head
• All 5 regions have a set group of vestibular hair cells with set orientations

Question 6

Vestibular hair cells

Answer 6

• Each grouping of hair cells (in sacculus, utricle, and 3 semi-circulars) has a set orientation
  o Multiple orientations allows you to detect movement in all axes and
  rotations
  o Hairs orientated in different directions in the 5 different components
• Finger like projections sit into gelatinous layer with particles of calcium crystals on top
  o Cilia bend – signal transduction – potential to afferent fibre
   Afferent fibre is a separate cell
• Project cilia into a ‘jelly’
  o In the utricle and saccule, otolith crystals sit atop the gelatinous layer
  o In the semicircular canals, the jelly is shaped into a dome = the cupula
   This is surrounded by endolymph fluid
   Too much fluid can restrict the movement of hair cells and alter
  vestibular sensation
   Crystals can become loose and float around – create movement

Question 7

Vestibular info

Answer 7

• The vestibular hair cell is the sensory neuron
• Cilia bending causing signal transduction neural signal generated
• Neural signals then transmitted to primary afferent neurons (axons for CNVIII)

Question 8

Process of vestibular sensation

Answer 8

1. Movement in relation to gravity
   o Specific stimulus – gravitational pull
2. Vestibular hair cells bend - signal transduction
   o Specific receptors responsive to the stimulus – vestibular hair cells respond to this and nothing else
3. Resulting neural potential handed off to primary afferent neurons
   o Axons form the vestibular branch of CNVIII
   o Not a specific relay path to the brain – share the nerve
    Criteria could be improved – this means auditory can’t be its own system either as it shares the nerve
    Difference branches of CNVIII
    Resulting qualia is distinct – use this to separate modalities
4. Neural signal synapses to vestibular nuclei in brainstem
   o One on either side
5. Neural signal ascends to cerebellum
   o Info from semicircular canals – ascending projections to cerebellum
6. Neural signal (sp. From otolith organs) also descends to spinal cord
   o Particular signals from otolith descend down as well as projection from cerebellum too

Question 9

vestibular pathway critical for:

Answer 9

-critical for balance, posture and movement
o Facilitate conscious movements, actions
o Facilitate unconscious compensations in posture and balance o Via excitation of extensor muscles
o Vestibular system gives postural and visual stability

Question 10

Compensatory reflexes

Answer 10

• Vestibular system enables certain reflexes that are important for survival
• Tail flick reflex in fish
  o Sudden movement of body-saccular hair cells bend
   Water pushes towards them
  o Message relayed vis CNVIII to brain stem
  o Synapses on Mauthner cells
  o Ipsilaterally: reflex initiated
   Motor message sent to spinal cord
   Result: flex muscles on this side
  o Contralaterally: Mauthner cell inhibited
   No motor message sent to spinal cord
   Result: muscles stay relaxed on this side
  o Net result
   Tail flick to one side, escape
   No cortical, just reflex

Question 11

Fall on your face reflex in humans

Answer 11

o Sudden movement of head-combination of hair cells bend
 Trips and falls
o Message relayed via CNVIII to brain stem
o Synapses on vestibular nuclei
o Ipsilaterally: reflex initiated
 Motor message sent to spinal cord + cerebellum
 Result: extend arm, lift head on this side
o Contralaterally: reflex initiated
 Motor message sent to spinal cord + cerebellum
 Result: extend arm, lift head on this side
o Net result
 Limb extension
 Head lift
 On both sides to break fall and protect face
 No cortical involvement at this level – fast

Question 12

Vestibulo-ocular reflex (VOR)

Answer 12

• Integration of eye movement and posture
  o Within brainstem, projections integrate with cranial nerves controlling eye movements
  o Rotate head left-keep gaze straight ahead by moving eyes to the right
   VOR
• Coordinated activity of CNVIII(vest) with CNIII(oculomotor) and CNVI(abducens)
  o Integrates circuit between 3 nuclei within the brainstem
  o Pull certain muscles to maintain gaze
  o Allows you to focus on something in front of your despite moving your head
   Keeps the visual scene still - This is an example of perceptual stability
  o Rapid changes in sensory stimuli are not perceived; perception is kept safe
  o Mechanisms that mean you don’t detect the changes
  o Important for fluidity of living
• Bilateral damage
  o Oscillopsia – perception of world moving when head moves
  o See the movement as you don’t have the mechanism to keep visual scene still
  – visual world moves as you do

Question 13

Functions of vestibular system

Answer 13

1. Inform on body position relative to gravity
   o Direction and speed of movement
   o Enables coordinated reflexes
   o Enables postural reflexes
2. Coordinate head and eye movement
   o VOR, permits gaze to remain fixed despite movement

Question 14

Vestibular dysfunction

Answer 14

• Dysfunction along any part of the pathway can impair vestibular performance
  o Vestibular labyrinth
   Infection (labyrinthitis)
   Pieces of loose otolith (positional vertigo)
   Can resolve by sitting and letting them settle
  o CNVIII
   Inflammation of nerve (vestibular neuritis)
   Vestibular branch or whole nerve
  o Vestibular nuclei
   Brain damage
  o Cerebellum
   Brain damage
   Transient dysfunction

Question 15

Clinical presentations
(Vestibular dysfunction)

Answer 15

o Vertigo
 + nausea
 Feel like body is moving when you’re not
o Nystagmus
 Tracking of the eyes
 Deficiency of VOR
 Pendular or jerk movements
 Eyes loop loose in the head, moving around in circular motions
 Used in sobriety tests
o Impaired VOR
 Aloric vestibular stimulation
 Irrigate the ear canal – caloric vestibular system
 Uses hot or cold water
 Hot – mimics head turning to the side
o Eyes move other way
 Cold – mimics head turning away from you
o Eyes go towards water side
 Are eyes working
 If VOR impaired – something wrong in brainstem
 Passively move head – eyes should jerk back to centre
o Impaired gait and balance
 Will more likely fall or lose balance
 If a sudden disruption and vestibular system senses sudden
movement
 Elicits reflexes to protect yourself
 Protect the head – easier to deal with a broken bone than brain damage

Question 16

Differences in specific gravity

Answer 16

• Usually, specific gravity of cupula = endolymph … things are in balance
• Once EtOH consumption starts, cupula (jelly) becomes lighter … things become imbalanced
  o Phase I PAN
  o Goes into the jelly before the rest of the fluid
  o Jelly gets lighter – hairs can move more easily and bend, perception of movement results
• Over time, EtOH diffuses into endolymph, cupula and endolymph re-gain equilibrium
  o Silent/intermediate period – 3-5 hours post alcohol cessation
  o Alcohol starts to go into fluid – positional vertigo starts to go away
   Jelly and fluid in balance
• As EtOH metabolises, cupula returns to normal specific gravity first, imbalance returns
  o Phase II PAN – 5-10 hours post alcohol cessation
  o Feel dizzy again – jelly returns to normal but liquid is still light
• Positional vertigo can persist for many hours after BAC=0

Question 17

Alcohol

vestibular dysfunction

Answer 17

oAffects cerebellum-impaired gait and balance
o Affects VOR-nystagmus, oscillopsia
oAffects cupula /endolymph homeostasis-vertigo
o Trip easily
 Less likely to correct themselves
 When drunk – see visual shifts when move head
 Get dizzy and goes away for a while and comes back as part of the hangover

Question 18

Motion sickness

Mismatch between visual and vestibular info

Answer 18

o Theories
-Brain comes to assumption
 Feeling like moving but things are still – maybe consumed something poisonous and should throw up
 Assumption that you are delirious
-Protective mechanism of body
 Different sensory input
 Goes into protection mode – throw up
 Go lie down somewhere – protect
 Resettle input because something isn’t right
-Can also get motion sickness in VR
 Mismatch where visually things are moving but the vestibular
body info says you're sitting still

Question 19

Syncing visual and vestibular in VR

Mismatch between visual and vestibular info

Answer 19

 Visual VR in its most basic form only works if you (your parietal cortex)
trusts visual info above all else
 Currently in VR a lot of the visual info mismatches any other incoming
sensory input
 But what if you could give your parietal cortex matching
visual-vestibular-auditory-etc. info  Galvanic vestibular stimulation
 Stimulating electrodes placed behind ears on temporal bone o Vestibular nerves, pick up pulse and give perception of
motion
 Stimulation pulses are synced to visual cues – eliminate motion
sickness
 You can steer people – directional navigation

Question 20

Excess fluid in inner ear - meniere’s disease

Mismatch between visual and vestibular info

Answer 20

o Meniere’s – too much fluid in middle ear
 Excess endolymph fluid in inner ear structure – making stuff bulge making inner hair cells not function properly
o Cause: idiopathic
o Symptoms: deafness, tinnitus, vertigo, feeling of pressure in ears o Median age of onset: 40s
o Diagnosis of exclusion
 Need to rule out everything else that could be causing the symptoms
 No diagnostic test
o Variable prognosis
 Drugs
 To treat symptoms
 Have to learn to live with
 Can come and go
 No cure for it – manage symptoms and learn how to function

Question 21

Mal de debarqument (MdD syndrome) – failure to desynchronise brain rhythms
(Mismatch between visual and vestibular info)

Answer 21

o Disembarkationsyndrome
 Subjective perception of self-motion after exposure to passive motion
o Transient MdD (<48hr) is very common and self-resolving
o Persistent MdD (days to years) is rare and pathological = MdD syndrome
o Idiopathic – MRI normal, inner ear function normal (inclusion criteria)
o Symptoms
 Feeling of motion, unsteadiness, distress, fatigue
o Median age reported
 ~55
 Overrepresentation of females
o Associated with increased occurrence of motion sickness, self-motion
sensitivity, visual sensitivity, and migrane
o Yoon-Hee Cha
 Maybe a functional network change while on the boat
 Brain create new rhythm for functioning processing – goes back to
normal when on land again
 Rhythm persists – abnormal synchrony of networks
 Keeps you in confused state of self-motion

Question 22

Giving yourself vestibular and proprio stimulation is important

Answer 22

• Sensory processing challenges/disorder are escalating in primary schools
• Kids seem to be getting worse off when it comes to
  o Balance
  o Bodyawareness
  o Coordination
  o Motoric learning
  o Acoustic spatial localisation
• Sensory processing disorders
  o Problems with incoming input and making sense of it
• Why is this
  o More awareness and understanding of ASD – recognition and knowledge
• Avoid this by
  o Getting enough input
  o Playing outside
  o Move around in the world

Question 23

Week 6 Vestibular System