Vestibular System

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 which runs in the internal acoustic meatus 
  • 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 runs synapses 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