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Neurology > Vestibular Function > Flashcards

Vestibular Function Flashcards

1
Q

Define the vestibular system?

A

A sensory system in the inner ear (embedded in temporal bone).
Its made up of fluid (endolymph) filled membranous channels or labyrinths

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2
Q

What makes up the vestibular system?

A

3 semicircular canals

  • Swellings at the base called ampulla
  • Connnected to Otolith organs (Utricle –> Saccule)
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3
Q

What does the vestibular system detect?

A

The semi-circular canals detect rotational acceleration

The otolith organs detect linear acceleration

  • Utricle = From/back tilt
  • Saccule - Vertical Movement
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4
Q

What is contained within the ampulla at the base of each semicircular canal?

A

An organ called Cristae made up of:
- A gelatinous cupulu within which sit the cilia of sensory hair cells (they then synapse to the vestibulocochlear nerve)

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5
Q

What types of cilia are there?

A

Each ampulla and otolith organ contains one large kinocilium and many smaller stereocilia

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6
Q

How do semi-circular canals detect rotational acceleration

A

As you rotate your head the ampulla moves but the intertia of the endolymph keep it stationary at first
This produces drag on the cupula which bends the cilia in the opposite direction to movement, triggering nervous impulses

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7
Q

Why do you feel dizzy, like your moving, when you stop suddenly?

A

The endolymphs inertia means it continues to move (and stimulate the cilia) after the ampulla stops

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8
Q

How do we tell which direction were moving in?

A

Cilia distorted towards the kinocilium –> Depolarisation –> Rise in APs

Cilia distorted away from kinocilium –> Hyperpolarisation –> Loss of APs

The cupula are also all in slightly different orientations so they are stimulated by different movements

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9
Q

Where does the brain integrate all the nervous impulses from the vestibular system?

A

Cerebellum

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10
Q

What do we call the sensory apparatus of the otolith organs?

A

Maculae

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11
Q

What plane are the maculae of the otolith organs in?

A

Utricle - Horizontal

Saccule - Verticle

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12
Q

Describe the structure of the maculae?

A

Cilia (Kinocilium and stereocilia) project into a gelatinous mass called the otolith membrane
Otoliths (CaCO3 crystals) embedded into the membrane

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13
Q

Why do maculae contain otoliths?

A

Because they are more effected by gravity than endolymph, so do a better job reacting to linear acceleration

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14
Q

How do the maculae detect linear acceleration?

A

Utricle:

  • Tilt the head back causes the ototlith to move with gravity
  • Pulls on the otolith membrane and so the cilia, towards the kinocilium
  • Depolarisation
  • Increased APs
  • And the opposite for forward tilt

The saccule does a similar thing for verticle movement

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15
Q

Moving your head causes a change in your centre of gravity, how does the body deal with this?

A

Vestibular nuclei get input from proprioceptos, neck and eye muscles regarding limb/body position.

Then projections from the vestibular nuclei project to the cerebellum via descending motor fibres (to handle posture/balance) and to the cerebral cortex via the thalamus (for conscious perception of movement and body position i.e. kinaesthesia)

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16
Q

What tracts are involved in vestibular reflexes?

A

Vestibulocortical and vestibulospinal tracts

17
Q

List the types of vestibular reflexes?

A
  • Tonic Labyrinthine Reflexes
  • Dynamic Righting Reflexes
  • Vestibulo-ocular Reflexes
    (including dynamic vestibular nystagmus & static reflex)
18
Q

What/how does the tonic labyrinthine reflex do?

A

It keeps the axis of the head in a constant relationship with the rest of the body

Uses the maculae & neck proprioceptors

19
Q

What does the dynamic righting reflex do?

A

Its a rapid postural adjustment to stop you falling when you trip

20
Q

Explain the nerves involved in the vestibulo ocular reflexes?

A

Its part of the association between the vestibular apparatus, visual apparatus and postural control.

Afferents from the vestibular nuclei (CN8) travel to the extraocular nuclei (CN3/4/6) to influence eye movement

21
Q

The static reflex is a type of vestibulo-ocular reflex, how does it work?

A

When you tilt you head your eyes intort/extory to maintain the image the right way up

22
Q

Explain the process of dynamic vestibular nystagmus?

A

Slow Compensation Phase:
Saccadic eye movements rotating the eye against rotation of the head so you maintain your gaze in the same direction

Rapid Phase:

  • Eyeball comes to the limit of its movement
  • Flicks back to facing straight ahead

The direction of the rapid phase is used when naming the nystagmus

23
Q

How do we define right vs left nystagmus?

A

The direction of the rapid phase

So if you turn your head left
--> Your eye rotate right to maintain vision
--> Reaches the limit
--> Flicks back left 
Therfore Left Nystagmus
24
Q

What two tests of vestibular function rely on vestibulo-ocular reflexes?

A

Post-rotary Nystagmus

Caloric Stimulation

25
Q

How does the post-rotary Nystagmus test work?

A

Subject rotated in a barany chair
Then when they stop accelerating and deceleration begins the nystagmus switches sides.

This because as you decelerate the endolymph inertia causes it to move faster than the ampulla so it starts pushing the cupulu in the opposite direction, tricking your brain about direction of movement

26
Q

How does caloric stimulation test vestibular function?

A
  • The outer ear is washed in cold or warm fluid which sets up convection currents in the endolymph

Warm fluid causes nystagmus towards the effected side, cold opposite.
(COWS - Cold opposite, Warm Same)

27
Q

What would cause pathological nystagmus?

A

Lesions of the peripheral or central vestibular pathways e.g. the brainstem

28
Q

How does motion sickness occur?

A

Kinetosis!
The Vestibular and visual inputs to the cerebellum are out of sync triggering a sickness signal from cerebellum to hypothalamus

29
Q

What are the symptoms of kinetosis?

A
  • N&V
  • Drop in BP
  • Dizziness
  • Sweat
  • Pallor
30
Q

What is labyrinthitis?

A

Infection interferes with vestibular function
Its acute
Triggers ANS symptoms and Vertigo
~May also have nystagmus and gross impairment of balance, it can be very disabling

31
Q

What is Meniere’s Disease?

A

Excess endolymph production causes a raise in inner ear pressure (Cause unknown)
–> Vertigo, nausea, nystagmus and tinnitus

32
Q

How can vestibular impairment be compensated for?

A

By the visual system, this happens over time as learning circuits are set up in the cerebellum
However the person will lose all balance in the dark or with their eyes closed

33
Q

NAme an ototoxic drug?

A

Streptomycin

34
Q

How does a brainstem lesion affect the vestibular system?

A

IT causes pathological nystagmus (At rest)

Neurology (50 decks)

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