Vestibular System (Dennis)

Question 1

Peripheral receptor apparatus

Answer 1

Inner ear

Head motion/position

Question 2

Central vestibular nuclei

Answer 2

In brainstem, takes and distributes info that controls motor and spatial stuff

Question 3

Vestibuloocular network

Answer 3

Aka vestibular nuclei, involved in control of eye movements

Question 4

Vestibulospinal network

Answer 4

Coordinates head movements, axial musculature and postural reflexes

Question 5

Vestibulothalamocortical network

Answer 5

Conscious perception of movement/spatial orientation

Question 6

Rotational head movements detected by

Translational head movements detected by

Answer 6

Semicircular canals

Otolith organs on the utricle and saccule hair cells

Question 7

Perilymph and endolymph

Answer 7

Perilymph lines the bony labyrinth while endolymph lines the membranous labyrinth
Endolymph dysfunction leads to vestibular disease

Question 8

What supplies the vestibular system?

Answer 8

Labyrinthine artery off the AICA
Also stylomastoid artery
Occlusion will compromise vestibular functions

Question 9

Meniere’s disease
Cause:
Clinical:

Answer 9

Increase in normal endolymph volume, resulting in distention of membranous labyrinth (hydrops)
Clinical: fluctuating hearing loss, vertigo, nystagmus, nausea, can’t stand etc.

Question 10

How do you treat Meniere’s?

Answer 10

Diuretic and self-restricted diet or implant a shunt to drain the endolymph

Question 11

Type 1 and Type 2 hair cells

Answer 11

Has lots of stereocilia and 1 kinocilium
Innervated by CN VIII
Stereocilia moving away and towards kinocilium de- or hyperpolarizes the cell

Question 12

Ampullae:

What happens here?

Answer 12

Hair cells cristae at the base of the ampulla and extend into the cupula
Rotational accelerations > displace endolymph > cupula bends to some side > displace the sterocilia

Question 13

Maculae:

What happens here?

Answer 13

Hair cells on the otolith membrane covered with otoconia on utricle and saccule
Linear acceleration > displace the otoconia > bend stereocilia

Question 14

Innervation to the vestibular system

Answer 14

Primary afferents from CN VIII from the ampullae and maculae project to the vestibular nuclei

Question 15

Vestibular nuclei:

Answer 15

Directionally selective. Record direction, speed of movement and head position
Has vestibulovestibular fibers and spinovestibular fibers

Question 16

Vestibulovestibular fibers vs. spinovestibular fibers

Answer 16

• reciprocal connections with analogous contralateral nucleus
• arise from all SC levels to provide proprioceptive input

Question 17

Vestibulocerebellar fibers pathway

Answer 17

From the vestibular nuclei course through the juxtarestiform body in the inferior cerebellar peduncle and to the cerebellum

Question 18

Primary vs secondary vestibulocerebellar fibers

Answer 18

Primary - target dentate nucleus, terminate as mossy fibers

Secondary - target the flocculonodular lobe, fastigial and dentate nuclei

Question 19

Cerebellovestibular fibers

Answer 19

Target vestibular nuclei

Control eye movements, head movements and posture

Question 20

Dizziness vs vertigo

Answer 20

Dizziness - spatial disorientation

Vertigo - spinning or turning, illusion of body motion

Question 21

Subjective vs Objective vertigo

Answer 21

Subjective: patient thinks they’re spinning
Objective: environment is spinning

Question 22

Benign paroxysmal positional vertigo

Answer 22

Otoconail crystals separate from the otolith and get lodged in the cupula (cupulolithiasis) leading to cupula deflections
Brief episodes of vertigo when changing body position

Question 23

Vestibular Schwannoma

Answer 23

Benign tumor in the cerebellopontine angle that originates in schwann cells of vestibular root. Tumor impinges the structures entering the internal acoustic meatus (CN VII, VIII and labyrinthine artery)
Hearing loss, gait difficulties and tinnitus

Question 24

Vestibular neuritis

Answer 24

Possibly caused by edema of the vestibular nerve. Patients usually have recent hx of URI
Severe vertigo, n, v, no hearing loss

Question 25

Lateral vestibulospinal tract

Answer 25

Arise from lateral and inferior vestibular nuclei > project to ipsilateral spinal cord
Extensor control for posture maintenance

Question 26

Topography of the lateral vestibulospinal tract

Answer 26

Anterorostral - cervical axons

Posterocaudal - lumbosacral axons

Question 27

Medial vestibulospinal tract

Answer 27

Arise from the medial vestibular nucleus > MLF > cervical SC
Stabilize neck and extensor muscles

Question 28

Vestibulocolic reflex

Answer 28

Medial vestibulospinal tract stabilizes head via activation of neck musculature

Question 29

How do vestibular info reach the thalamus?

Answer 29

All vestibular nuclei project to the VPM of the thalamus

Target the primary somatosensory cortex, parietoinsular vestibular cortex and posterior parietal cortex

Question 30

Lesions in the parietoinsular and posterior parietal cortices

Answer 30

• vertigo, unsteadiness

- confusion in spatial awareness

Question 31

Vestibuloocular reflex

Answer 31

Head rotations > activate semicircular canals > vestibular input about head motion > counter rotation of eyes > stabilize your eye while head is moving

Question 32

Slow phase vs fast phase movement

Answer 32

• counter rotation (eye directed to direction opposite of head rotation)
• reset the eye rapidly (reach limit of the eye turning that far, reset to central position)

Question 33

Nystagmus

Answer 33

Exaggerated slow and fast phase eye movements. Repetitive uncontrolled movements. Basically cannot fixate

Question 34

Spontaneous nystagmus

Answer 34

Unilateral damage to vestibular system. No input from the side of the damaged vestibular system
Causes spontaneous nystagmus, vertigo

Question 35

Peripheral damage to vestibular system:

Answer 35

Usually labyrinth damage or CN VIII damage. Causes imbalance of input between left and right systems

Question 36

Central damage to vestibular system

Answer 36

Localized to brainstem or cerebellum. Will also affect other pathways, not just vestibular system
Impaired voluntary saccades and smooth pursuit.

Question 37

What is the caloric test?

Answer 37

Test vestibular labyrinth function without moving head.
Use water to alter the endolymph > alters CNVIII firing rate.
Warm water = mimic turning head to irrigated side while cold induces opposite effect

Question 38

COWS

Answer 38

Cold Opposite side Warm Same side

Question 39

Oculocephalic reflex

Answer 39

Rotate head, patient’s eyes should stay focused centrally. If not, then you get doll’s eyes. Indicates brainstem dysfunction
Only works for comatose/unconscious patients, since conscious patients can voluntarily control their eye movement