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Neuroscience III (Sara) > Vestibular System > Flashcards

Vestibular System Flashcards

1
Q

Function of the vestibular system

A
  1. Sensing and perceiving self motion
  2. Postural control (orient to vertical, stabilize head, control COM)
  3. Stabilize gaze
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2
Q

Components of vestibular system

A
  1. Peripheral sensory (semicircular canals; otoliths)
  2. Central (vestibular nuclei; cerebellum)
  3. Motor output (VOR, VST)
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3
Q

Lateral SCC

A

Angled 30 degrees up in front and down in back from horizontal

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4
Q

Anterior SCC

A

Oriented vertically

35 degrees from sagittal

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5
Q

Posterior SCC

A

Oriented vertically

51 degrees from sagittal

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6
Q

Perilymph

A
  • Fills bony labryinth
  • Fills subarachnoid space
  • Low viscosity, high sodium, low potassium
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7
Q

Endolymph

A
  • Fills membranous labryinth

- High viscosity, low sodium, high potassium

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8
Q

How do the canals work?

A
  • Canals detect angular acceleration (good at high velocity motions)
  • Canals are paired –> lateral canals with each other; anterior canal works with posterior canal on opposite side
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9
Q

Push-pull arrangement

A

Equal and opposite response of complimentary canals (ex. increase firing rate on R, decreased firing on L)

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10
Q

Baseline firing rate

A

80-100 spikes/second

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11
Q

Inhibitory cut off

A
  • When the head turns 180 degree/sec velocity, only information available comes from increased firing rate side
  • Decreased firing rate side has no input
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12
Q

Otoliths

A
  • Utricle (horizontal) & Saccule (vertical)

- Detect linear acceleration and head position relative to gravity/vertical

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13
Q

Vestibular Nerve

A
  • Superior division: Anterior and lateral SCC, utricle, part of saccule
  • Inferior division: Posterior SCC, rest of saccule
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14
Q

Blood supply

A

PICA & AICA

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15
Q

Afferents of the vestibular nuclei

A
  1. Cervical spinal cord
  2. Semicircular canals
  3. Otolith
  4. Vestibulocerebellum
  5. Visual
  6. Other somatosensory collaterals
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16
Q

Efferents of the vestibular nuclei

A

1, Project back to peripheral apparatus

  1. Project to vestibulocerebellum
  2. Descending - Lateral and medial vestibulospinal tracts
  3. Ascending - CN III, IV, VI for eye movements
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17
Q

Vestibulospinal Reflex (VOR)

A

Goal: To maintain postural stability

Primary stimulus is head tilt - activates med and lat VST to keep posture

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18
Q

Gaze Stabilization

A

Goal: To keep image on fovea with head movement for clear vision
-Depends on VOR, COR, and optokinetic nystagmus

19
Q

Effective VOR depends on

A
  1. Accurate peripheral input
  2. Effective vestibular drive of eye movement
  3. Intact cranial nerves of eye movement
  4. Coordination of cerebellum
20
Q

Vestibular-ocular reflex

A
  • Stimulus: Head movement

- Can generate VOR in any direction because specific canals drive specific eye movements

21
Q

Cervico-ocular reflex

A
  • Goal: To contribute to gaze stabilization
  • Stimulus is neck movement
  • Compensates for 15% of eye movements
22
Q

Optokinetic Nystagmus

A

-Goal: To keep moving image fixed on retina

23
Q

Peripheral disorders

A
  1. Reduced function
  2. Distorted function
  3. Fluctuating function
24
Q

Acute unilateral loss

A

-Reduced function peripheral disorder

Vertigo towards contralateral side; spontaneous nystagmus to contralateral side

25
Bilateral hypofunction
-Reduced function peripheral disorder | Only notice dysequilibrium at rest; notice dysequilibrium, dizziness, oscillopsia, nausea/vomiting with movement
26
Post-vestibular neuritis
- 2nd most common cause of vertigo - Severe vertigo, spontaneous horizontal nystagmus, imbalance, nausea - Can be idiopathic but usually follows respiratory infection - Improves 48-72 hours and resolves within 6 weeks - Treated with vestibular supressants
27
Treatment of reduced function peripheral disorders
- Compensate via mechanisms in CNS | - Vestibular rehab to decrease visual dependence and increase vestibular dependence
28
Distorted function
- Ex. BPPV - vertigo in certain positions - Theories: Cupuloithiasis & Canalithitis - Treatment: Maneuvers
29
Fluctuating function
- Occasional or intermittent disruption of vestibular input - Least amenable to physical therapy - Meniere's Disease - Perilymph Fistula - Other causes: Autoimmune disease, infections, migranes
30
Meniere's Disease
- Abnormal endylymphatic sac function - Sac expands and puts pressure on nerve then suddenly releases built up endolymph - Episodes of hearing loss - Acute symptoms 24-36 hours with cumulative loss over time - Treatment focuses on education and HEP
31
Perilymph fistula
Fistula between middle ear and perilymph in perilymphatic sac - Symptoms precipitated by auditory stimulus or change in air pressure - Caused by: Head trauma, barotrauma, surgery, penetrating injury
32
Central lesion etiology
1. Vascular 2. Tumor 3, Degenerative/aging 4. Trauma
33
Central lesion locations
1. Vestibular nuclei 2. Cerebellum 3. CNS areas (reticular formation) 4. Visual pathways 5. Motor output
34
Signs of central lesion
- Direction changing nystagmus | - Inability to cancel VOR
35
Central disorder treatment
- Promote upregulation of vestibular function through exercises - Not as much research on central rehab versus peripheral rehab
36
Central v. Peripheral nystagmus
- Peripheral: Will fatigue, will be compensated by CNS | - Central: Will not fatigue, gaze evoked/spontaneous/direction changing nystagmus
37
Advantages of caloric testing
- Test right and left ear separately - May assist in localizaing side of damage - Easy to perform, inexpensive
38
Disadvantages of caloric testing
- Effect of stimulus differs across individuals - Primarily tests horizontal SCC, not anterior/posterior - Generates low frequency stimulation, below optimal operation range of vestibular receptors - Not calibrated
39
Advantages of rotary chair test
- Less variability than caloric testing - Better at detecting bilateral dysfunction - May help determine central compensation from vestib rehab
40
Disadvantages of rotary chair test
- Stimulates L and R side simultaneously - Tests only horizontal SCC and portion of superior vestibular N - Expensive - Difficult to determine side of lesion
41
Compensation
How CNS recovers from vestibular dysfunction, including adaptation and stimulation
42
Adaptation
- Increasing gain of VOR - Goal: 1. Decrease retinal slip and increase VOR gain; 2. Fine tune VSR and other balance reactions - Context specific: get what you train
43
Substitution
-What is able to do this: COR, visual tracking with smooth pursuit, substitution of visual and somatosensory info, saccadic corrections, anticipatory saccade

Neuroscience III (Sara) (4 decks)

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