vestibular

Question 1

hair cell preferred direction

Answer 1

towards longest hair = preferred direction → depolarisation → increase firing rate (from resting)

Question 2

central pathways

Answer 2

1. ocular motor nucleus (right next to superior colliculus) → stabilise eyes
   
   • info about head movement from vestibular and visual systems control eye movement to help keep stable image on retina
2. neck motor neurons → stabilise head
3. cerebellum and spinal cord → maintain balance (→ brain modifies movement/contraction of skeletal muscle)

Question 3

vestibular nerve projections

Answer 3

• vestibular nerve = part of CNVIII
• projects to medulla oblongata and pons → cerebellum
• some fibres also straight to the cerebellum (the only sensory nerve that goes straight to cerebellum - role in balance)
• some fibres descend to spinal cord

Question 4

The vestibulo-ocular reflex (VOR)

Answer 4

• input from vestibular nerve (CNVII) to brainstem
• integrated here
• within brainstem, CNVI (abducens) responsible for motor movements of eye; & projection to midbrain
• Within midbrain, CNIII (oculomotor)

VOR requires coordinated activity of all 3

Question 5

Loss of VOR - disorders

Answer 5

• nystagmus → eyes can’t be stabilised
  
  • if vestibular involved → vertigo and balance issues
• oscillopsia → ‘jumping vision’, objects/words don’t appear stable, they jump/shake/vibrate

Question 6

Ménière’s disease

Answer 6

• idiopathic endolymphatic hydrops (excess
  fluid in the inner ear)
• symptoms
  
  • Recurrent spontaneous episodic vertigo,
  • fluctuating hearing loss,
  • aural fullness or pressure, and
  • tinnitus