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Neuro 3 > Vestibular > Flashcards

Vestibular Flashcards

1
Q

What are three functions of the vestibular system?

A

Sensing and perceiving self motion
Postural control (orienting to vertical, stabilizing head, controlling center of mass)
Stabilize gaze

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2
Q

What are the parts of the peripheral sensory apparatus?

A

Semicircular canals
otoliths
vestibular nerves

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3
Q

What are the central processors of the vestibular system?

A

Vestibular nuclei

cerebellumV

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4
Q

What are the motor outputs of the Vestibular system?

A

estibulo-occular and vestibulospinal reflexes

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5
Q

Where is the Chochlea located? The labyrinth? What is the labyrinth?

A

Cochlea is anterior

Labyrinth (otolith and semicircular canals) is posterior and lateral

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6
Q

How many semicircular canals are there?

A

3 anterior, posterior and lateral

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7
Q

What does the otoliths consist of?

A

Utricle and saccule

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8
Q

what is the membranous labyrinth?

A

a closed system that lines the bony labyrinth which is filled with endolymph (high viscosity, low sodium, high potassium).

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9
Q

What type of fluid is between the bony and membranous labyrinth?

A

perilymph-low viscosity, high sodium, low potassium

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10
Q

Difference in viscosity between perilymph and endolymph.

A

perilymph is low viscosity (high Na, low K+)

Endolymph-high viscosity (low Na, high K+)

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11
Q

What is the ampulla?

A

at the end of each canal there is an expanded portion which is a specialized receptor area of the semicircular canals

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12
Q

What is the crist?

A

A small bump in the ampulla where the receptor hair cells, stereocilia, are located

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13
Q

What covers the crist, hair cells and stereocilia?

A

The gelatinous cupula, which is exposed to endolymph

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14
Q

What type of acceleration do the canals detect?

A

Angular acceleration

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15
Q

Why does endolymph lag with head movement? What does the endolymph do to the hair cells?

A

increased viscosity pushing on the cilia receptors to fire proportionally to head velocity

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16
Q

When are the hair cells particularly active?

A

During the beginning and end of movements

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17
Q

What happens if the stereocilia bend towards the kinocilia?

A

depolarization occurs and results in an increase firing rate

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18
Q

What happens if the stereocilia bends away from the kinocilia?

A

hyperpolarization resulting in decreased firing rate

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19
Q

Where do the stereocilia generate a nerve impule?

A

Generate an impulse down CN VIII (vestibulocochlear)

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20
Q

what is the baseline firing rate of CN VIII?

A

80-100 spikes/sec

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21
Q

What is the push pull arrangement in the canals?

A

Each canal is paired with the opposite canal (L anterior to R posterior & vice versa, lateral canals to each other) when one canal is stimulated the other is inhibited

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22
Q

What happens if the head moves at 180deg/sec?

A

The opposite canal will be inhibited to zero, cannot detect movement quicker than 180deg/sec (we can move at 300 deg/sec)

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23
Q

What plane is the saccule oriented? The utricle?

A

Saccule-vertical

Utricle-horizontal

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24
Q

What is the receptor area in the otoliths called?

A

The macula

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25
Q

What type of acceleration does the otoliths detect?

A

Linear

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26
Q

What makes otoliths sensitive to gravity?

A

Calcium carbonate crystals called otoconia which add mass to otolithic membrane

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27
Q

When will the otoliths have increased firing rates?

A

Unlike the semicircular canals which have an increased firing rate at the beginning and end of movement, otoliths have an increased firing rate during the duration of movement (due to gravity and the otoconia)

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28
Q

What type of firing does the semicircular canals have? Otoliths?

A

SC canals-phasic

O-tonic

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29
Q

Function of otoliths

A

detects head position relative to verticle which is transmitted to cerebral cortex and vestibular nuclei

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30
Q

The superior vestibular nerve innervates what?

A

lateral and anterior SCC

Utricle

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31
Q

The inferior vestibular nerve innervates the what?

A

Posterior SCC and saccule

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32
Q

Blood supply to the peripheral apparatus?

A

Labyrinthine artery

33
Q

Blood supply to the Central vestibular structures?

A

AICA and PICA

34
Q

Vestibular nuclei efferents?

A
  • Back to the peripheral apparatus to modify hair cell firing
  • vestibulocerevellum
  • decending projections (med/lat Vestibulospinal tract)
  • Ascending projections-via MLF to CN III, IV , VI for eye movement and via thalamus to cortex for sensation
35
Q

What coordinates all vestibular output and reflexes?

A

Flocculonodular lobe (vestibulocerebellum)

36
Q

Goal of the Vestibulospinal reflex?

A

to maintain postural stability

37
Q

What is the VSR in response to?

A

Head tilting and gravity

38
Q

During the VSR, what side is the flexor response and what side is the extensor response on?

A

extensor response on side to which head is inclined

Flexor response on opposite side

39
Q

What is the goal of the VOR?

A

Gaze stabilization. It drives eye movement in response to head movement

40
Q

What coordinates the VOR?

A

The cerebellum

41
Q

What is the goal of the vervical occular response?

A

Contribute to gaze stabilizatoin. It is responsible for 15% of compensatory eye movement in response to head movement

42
Q

What joint gives inputs to the COR?

A

cervical facet joint receptors

43
Q

What is the goal of optokinetic nystagmus?

A

to keep moving image fixed on retina

44
Q

What is the difference between VOR/COR and optikonetic nystagmus?

A

In VOR/COR head is moving

Optokinetic nystagmus the head is still

45
Q

What are the two phases of optikokinetic nystagmus?

A

slow phase to follow object

fast saccadic movement is recovery phase to reposition eye

46
Q

What are sources of physiological nystagmus?

A

End point nystagmus (in 30% of ppl)
Nystagmus with spinning
Optokinetic nystagmus
Nystagmus with caloric testing

47
Q

Pathological nystagmus?

A

May be spontaneous, positional or evoked

48
Q

How is nystagmus named?

A

In the direction of the fast segment

49
Q

What happens to the nystagmus when you stop spinning?

A

the endolymph keeps moving so you will see the nystagmus in the opposite direction

50
Q

Definition of vertigo?

A

sense of movement

51
Q

Definition of disequillibrium?

A

Loss of balance

52
Q

Definition of Oscillopsia?

A

Visual field is moving, unstable

53
Q

Three categories of peripheral disorders?

A

Reduced function
distorted function
fluctuating function

54
Q

Types of reduced function peripheral disorders?

A

decreased fxn of either receptors or vestibular nerve
either uni or bilateral
comlete or incomplete

55
Q

Is peripheral hypofunction amenable to treatment?

A

yes

56
Q

Why is vertigo a symptom of acute unilateral peripheral vestibular loss?

A

brain senses that you are spinning due to the relative mismatch in firing rates of both sides

57
Q

Would you have spontaneous nystagmus with unilateral vestibular loss?

A

Yes in the same direction as the lesion?

58
Q

Would you have spontaneous nystagmus after bilateral vestibular loss?

A

No b/c brain cannot detect movement from vestibular system and cannot generate VOR

59
Q

2nd most common cause of vertigo?

A

Post vestibular neuritis

60
Q

How long does it take for Post vestibular neuritis to improve? To resolve?

A

Usually 48-72 hours. Resolves usually in 6 weeks

61
Q

Some causes of peripehral hypofunction

A

Age related changes
Ototoxicity
Traumatic VIII th nerve damage
Post-surgical acoustic neuroma

62
Q

What is the most common form of distorted vestibular function? Is it amenable to treatment?

A

BPPV. ALso most common form of vertigo. it is amendable

63
Q

Whay is Cupulolithiasis?

A

Part of the otoconia from utricle dislodges and floats into canal, adhering to cupula (little to no latency to nystagmus)

64
Q

What is canalithiasis?

A

Free floating debris in canal (longer latency to nystagmus)

65
Q

Why is the posterior canal most often affected?

A

Ampulla of the posterior canal is below the utricle so the debris from the utricle easily falls into the PCC

66
Q

How can a nystagmus from a peripheral source be suppressed?

A

By visual fixation

67
Q

What are frenzel lenses?

A

Lenses that make it easier for examiner to see the nystagmus and prohibits pt from fixating visually and suppressing the nystagmus

68
Q

What disease is typical of fluctuating function vestibular damage?

A

Meniere’s disease, which is abnormal endolymphatic sac function whereby sac expands and puts pressure on nerve, the releases built up endolymph

69
Q

What sensory loss is associated with Meniere’s disease?

A

Hearing loss and/or vestibular dysfunction

70
Q

How long does full recovery take?

A

Days to weeks

71
Q

What is the treatment of Meniere’s disease?

A

Usually focused on education and HEP as well as prevention of secondary impairments. If severe surgery to remove endolymphatic sac

72
Q

What is a perilymph fistula?

A

Another form of flucuatinf fxn where there is a fistula btwn middle ear and perilymph

73
Q

What can cause a Perilymph fistula?

A 
head trauma
barotrauma
surgery
penetrating injury
Autoimmune disease
infections
migranous
74
Q

What is VOR cancellation?

A

When you turn head and move eyes with head. This is an override of the VOR by CNS

75
Q

What does an inability to cancel the VOR indicate?

A

CNS involvement

76
Q

What is a doll’s head maneuver?

A

VOR in a comatosed patient. Positive Doll’s head indicates intact brainstem while negative Dolls head can indicate lower brainstem damage

77
Q

Is there good evidence for treating central disorders?

A

Not good evidence

78
Q

Will a central nystagmus fatigue? Peripheral?

A

A central nystagmus will not fatigue. A peripheral will

Neuro 3 (5 decks)

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