09 16 2014 Vestibular System

Question 1

Vestibular system tasks?

Answer 1

1. controls reflexive eye movements
   - cerebellum and oculomotor nuclei
2. Vestibulo-ocular reflexes keep the eyes still when the head moves
3. vestibulospinal reflexes : enable the skeletomotor system to compensate for head movements

Question 2

Symptoms of vestibular system disease?

Answer 2

Vertigo vs. dizziness (with feeling of the world spinning)

Nauseau, vomiting, pallor, perspiration

Difficulty walking

Sensation of spinning or rhythmic movements

Nystagmus (jerky eye movements

Question 3

Oscillopsia

Answer 3

vestibular damage that makes it difficult or impossible to fixate on visual targets while head is moving.

-feel like the words is spinning around you

Question 4

Blood supply to labyrinth?

What would happen if there is a stroke in this area?

Answer 4

AICA

-sudden hearing loss and vertigo

Question 5

Semicircular canals

Answer 5

• angular acceleration : rotation
• functions in paris with opposite canal on opposite ear
• hair cells are in ampulla. Hair cells in ampule are covered by a gelatinous mass called a CUPULA.
• Cupula has weight and when head moves it lags behind and bends hair cells

Question 6

Direction of hair cells in Semicircular canals

Answer 6

Anteriror : Facing up and away from utricle

Horizontal: slightly down and towards utricle.

Posterior: Horizontal

Question 7

Utricle

-what is in it?

Answer 7

Macula: thick sensory epithelium with hair cells oriented in the horizontal plane.

Also has otoconia (calcium carbonate crystals) embedded in otolithi membrane
-displacement = action potential

Question 8

Saccule

Answer 8

Macula: thickened epithelium with hairs oriented in the vertical plane

-responds to linear acceleration in vertical plane.

Question 9

Movement that Saccule and Utricle comprehend?

Answer 9

Linear acceleration of head (in any direction) AND static head position

Question 10

Striola

Answer 10

utricle and saccular areas are divided by a striola– just an area that divides hair population having opposite polarities

Question 11

BPPV?

Answer 11

Benign Paroxysmal positional vertigo

• otoconia detaches from otolithic membrane of the utricle and it gets stuck in the semicircular canal.
• • obstruct flow of cupula

Usually unilateral but can sometimes be bilateral

Question 12

Lateral vestibular nucleus controls what?

Answer 12

posture, vestibulo-spinal reflexes

Question 13

medial and superior vestibular nuclei control what?

Answer 13

vestibulo-ocular reflexes; vestibulo-cervical reflexes

Question 14

Inferior vestibular nucleus does what?

Answer 14

integration of inputs from the vestibular labyrinth and the cerebellum

Question 15

Medial and superior vestibular nuclei innervation?

Answer 15

• receives fibers predominantly from the semicircular canals
• efferents include MLF, oculomotor nuclei, and cuddly to spinal cord

-Medial vestibular nuclues –> medial vestibular tract = vestibulo-cervical reflexes.

Medial nucleus efferents are excitatory
Superior nucleus efferents are inhibitory

Question 16

Lateral vestibular nucleus innervation?

Answer 16

aka Deiter’s nucleus

-Afferents from semicircular canals and otolithic organs.

Efferents mostly to the lateral spinovestibular tract.

Largely conceded with postural control

Question 17

Inferior (descending) vestibular nucleus innervation?

What is this nucleus mostly concerned with?

Answer 17

Afferents from otolithic organs and cerebella cortex (purkinje cells)

Efferents mostly to cerebellum and reticular formation, contralateral vestibular nuclei and spinal cord.

Concerned with integrating central motor signals with vestibular input

Question 18

Lateral vestibulospinal tract

Answer 18

Ipsilateral
Principal pathway by which otolithic organs can regulate bodies extensor organs

major source: LVN
minor contributor: SpVN

Question 19

Medial Vestibulospinal tract

Answer 19

Bilateral
projects through MLF

Major source: MVN

Mainly cervical
Vestibulo-cervical reflexes

Question 20

Vestibulothalamic projections

Answer 20

ascending pathway (poorly understood)

• Ventroposterolateral (VPL), pars oralis
• Bilateral projections
• tend to arise from the medial vestibular nucleus.

Other targets are VP, VL, and intralaminar nuclei.

Question 21

Nystagmus

Answer 21

typical to side contralateral to the dysfunction of vestibular apparatus

involuntary rhythmic movements of the eyes consisting of a rapid movement in one direction and a slow movement in the opposite direction

Question 22

Caloric test

Answer 22

irrigating the external auditory meatus with warm or cold water.

Nystagmus towards warm water and away from cold water.

Question 23

Optikinetic Nystagmus

Answer 23

fast component in the opposite direction to that of the moving lines

-ex. looking at telephone poles while in passenger seat in car

Question 24

Vestibular-occular-reflex (VOR)

Answer 24

particular system that produces eye movements that counter movements of head

-permit gaze to remain fixed on a particular point.

Question 25

Vertigo vs. dizziness

Answer 25

vertigo– spinning sensation of movement

Dizziness: light headedness, nausea, unsteadiness on one’s feet

Question 26

vestibular neuritis

Answer 26

inflammation of vestibular ganglia or fever due to a viral infection or idiopathic inflammation

Question 27

acoustic neuroma

Answer 27

cerebellopontine angle tumors

onset: 50 yrs of age

Occurs at the point where CN 8 enters the internal auditory meatus.
-early symptom: tinnitus (unilateral) and unsteadiness

Question 28

positional testing

Answer 28

helps identify BPPV of any of the semicircular canals and other causes for positional dizziness

Question 29

central vs. peripheral vertigo

and nystagmus

Answer 29

Peripheral lesions: delay of 2- 5 secs before the onset of nystagmus and vertigo.

• horizontal or rotational
• fades within 30 secs
• fades with adaptation to tests

Central lesions: nystagmus and vertigo begin immediately and there is no adaptation.

• horizontal or rotary nystagmus
• • Vertical nystagmus, nystagmus that changes directions while remaining in the same position, nystagmus in the absence of vertigo is ONLY CENTRAL.

Question 30

Gaze nystagmus

Answer 30

have patient gaze no more than 30 degrees from front. If there is a problem, the nystagmus is contralateral to the dysfunctional side

Question 31

Positional nystagmus

Answer 31

nystagmus is induced by particular head positions. These patients are particularly troubled by vertigo

Question 32

can the vestibular system adapt?

Answer 32

Yes

-astronaut – goes to space (no gravity) comes back to earth (gravity)