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Vestibular System

Topic updated on 05/15/17 6:03pm

Overview
 

 
Introduction
  • Vestibular system
    • angular acceleration of the head is detected by the semicircular canals
      • this is secondary to endolymph movement via the ampulla
        • the hair cells will then send excitatory input into the primary sensory neuron which have their cell bodies in the
          • vestibular ganglia (of Scarpa) which send axons via the
            • vestibular nerve
    • linear acceleration of the head and head tilt is detected by maculae (which is contained within the utricle and saccule)
      • maculae contain otolith (calcified crystals)
        • otolith may be pulled with linear acceleration and activate hair cells which
          • excites primary sensory neurons → vestibular ganglia → vestibular nerve
            • vestibular nerve synapse to the vestibular nuclei which then relays to other structures within the central nervous system such as
              • medial longitudinal fasciculus
                • which mediates the vestibulo-ocular reflex
              • spinal cord
              • cerebellum (e.g., flocculonodular lobes and vermis)
              • cerebral cortex via the thalamic ventral posterior nucleus
  • Clinical correlate
    • caloric testing
      • a test that stimulates the vestibulo-ocular reflex via
        • warm or cold water infusion into the ear
      • normal findings
        • warm water
          • nystagmus with the fast phase towards the side of infused water
        • cold water
          • nystagmus with the fast phases towards the opposite side of infused water
        • mnemonic
          • COWS (Cold Opposite, Warm Same)
    • nystagmus
      • describes rhythmic movements of the eye which can result from
        • an asymmetric vestibular inputs
    • vertigo
Summary of Peripheral Vs. Central Vertigo
Vertigo Type
Etiology
Differential Symptoms
Peripheral vertigo
  • Lesion affecting the
    • vestibular apparatus (in the inner ear)
    • cranial nerve VIII
  • Benign paroxysmal positional vertigo (BPPV)
  • Vestibular neuritis
  • Meniere's disease
  • Acoustic neuroma
  • Aminoglycoside toxicity
  • Semicircular canal dehiscence syndrome
  • Perilymphatic fistula
  • Herpes zoster oticus (Ramsay Hunt syndrome)
  • Intermittent and positional vertigo
  • Can be associated with tinnitus as well as
    • hearing loss
    • postural unsteadiness
  • Nyastagmus is
    • delayed in onset
    • rotatory or horizontal
    • prominent if vertigo is present
    • adaptive
  • Vertigo stops with visual fixation
Central vertigo
  • Lesion affecting the
    • brainstem nuclei
    • cerebellum
  • Vestibular migraine
  • Brainstem stroke
  • Multiple sclerosis
  • Ischemic or hemorrhagic damage to the cerebellum
  • Non-positional vertigo
  • May accompany other cranial nerve injuries such as
    • facial droop
    • dysarthria
  • Nystagmus is
    • immediate or delayed in onset
    • rotatory, horizontal, or vertical
    • not adaptive
  • Vertigo does not stop with visual fixation
 


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