Vestibular System

Question 1

Functions of the vestibular system

Answer 1

• sensory info about head movements & head position relative to gravity
• gaze stabilization: control of eye movements when head is moving
• postural adjustments/balance
• autonomic functions

Question 2

Organization of the vestibular system

Answer 2

• vestibular apparatus/inner ear/labyrinth –> CN VII –> 4 vestibular nuclei (pons/medulla) –> 6 outputs involving vestibular information

Question 3

Vascular supply to vestibular system

Answer 3

• labyrinthine artery
• mostly branches off of the AICA
• occlusion can cause dizziness & auditory symptoms
• divides into Anterior vestibular artery and Common cochlear artery
• Anterior vestibular artery: dizziness symptoms only, supplies the vestibular nerve, utricle, horizontal, & anterior semicircular canals
• Common cochlear artery: dizziness and auditory symptoms, supplies the cochlea, saccule, & posterior semicircular canal

Question 4

Vestibular apparatus

Answer 4

• ampulla of the 3 semicircular canals
• macula which contains the article & saccule and otoconia (crystals)
• hair cells in the semicircular canals bend as endolymph pushes cupola with angular movements
• hair cells in utricle/saccule bend due to gravity or with linear acceleration/deceleration

Question 5

Orientation of the semicircular canals

Answer 5

• Horizontal: points 30 degrees up and detects head rotation
• Posterior: angled the same as your ear
• Anterior: perpendicular to the posterior
• Anterior and posterior canals detects diagonal movements

Question 6

Activation/inhibition of hair cells by bending

Answer 6

• resting rateis 90 spikes/sec
• deflection of the hair cell towards the kinocilia = excitatory output
• deflection of the hair cell away from the kinocilia = inhibitory output

Question 7

Turning your head to the right

Answer 7

• semicircular canals work in pairs to detect angular movements
• horizontal canals are being used
• right SC canal will be activated while left SC canal will be inhibited

Question 8

What canals talk to one another

Answer 8

• horizontal canals talk to each other
• left anterior and right posterior talk to one another (LARP)
• right anterior and left posterior talk to each other (RALP)

Question 9

Utricle and saccule

Answer 9

• they detect linear movements while SC canals detect rotational movements
• 4 total meaning one pair in each ear
• utricle is oriented horizontally, responds to horizontal linear acceleration/deceleration & forward/backward head tilts
• saccule is oriented vertically, responds to vertical linear movements & leaning sideways

Question 10

Dizziness/Vertigo

Answer 10

• illusion of motion/spinning
• impaired gaze stability with head movements & blurry vision due to impaired VOR
• can be associated with nystagmus which could be spontaneous or triggered by positional changes

Question 11

Nystagmus

Answer 11

• repetitive involuntary beating movements due to inaccurate signals coming in from peripheral vestibular systems (SC or CN VIII) or impairments in central vestibular processing centers (brainstem or cerebellum)
• more severe in peripheral than central lesions
• can be physiologic

Question 12

Laws of nystagmus for peripheral lesion

Answer 12

• Alexander’s Law: the amplitude of the nystagmus increases when the eye moves in the direction of the fast phase
• Ewald’s Law: movement of the eyes during nystagmus occur in the plane of the stimulated canals

Question 13

Vestibular neuritis

Answer 13

• a peripheral lesion in the vestibulocochlear nerve

Question 14

Left posterior canal BPPV

Answer 14

• a peripheral lesion with otoconia crystals dislodged from utricle/saccule that have entered the left posterior canal
• there will be a latency or a duration & then the nystagmus will stop

Question 15

End gaze nystagmus

Answer 15

• normal
• everyone has a little nystagmus when straining the eye to look at end range

Question 16

Pathologic nystagmus

Answer 16

• due to central lesions
• beats in the direction they are looking
• direction changing beating
• purely vertical nystagmus = central nystagmus

Question 17

Peripheral vestibular disorders

Answer 17

• Vestibular hypofunction: vestibular neuritis, perilymph fistula, or Ménière’s disease
• BPPV: poster SC, horizontal SC, or anterior SC

Question 18

Central vestibular disorders

Answer 18

• stroke in brainstem/cerebellum
• cerebellar degeneration
• Arnold-Chiari malformation

Question 19

Characteristics of nystagmus from peripheral lesions

Answer 19

• direction fixed beating
• follow Alexander’s law: beats fast when eye moves toward the fast phase and beats in the plane of the impaired canal
• able to fixate with gaze stabilization
• habituates/compensates rapidly with time
• good outcomes with vestibular rehab

Question 20

Characteristics of nystagmus from central lesions

Answer 20

• pure vertical beating
• direction changing beating
• unable to fixate with gaze stabilization
• does not follow Alexander’s law
• take longer to habituate/compensate
• worse than peripheral outcomes for vestibular rehab

Question 21

Oscillopsia

Answer 21

• patient complains of shaky/jumpy visual world with movements

Question 22

Head impulse test

Answer 22

• can expose weak vestibular system on one side
• clinical test for VOR function
• patient is asked to keep gaze on target while the therapist performs rapid head movement
• Positive = retinal slip with shift of gaze towards direction of head movement followed by a corrective saccade at the ned of head movement
• must rotate head at a minimum of 200 degrees/sec

Question 23

Other symptoms of vestibular disorders

Answer 23

• impaired postural control
• ataxia: poor coordination
• dizziness
• nausea
• vomiting