• The vestibular system functions to maintain an animal's balance and orientation with respect to gravity
          o Maintains steady visual image by stabilizing the eyes during head movement
          o Maintains steady body position by stabilizing head positioning in space

     • Clinical anatomy
          o Peripheral components – within inner ear, petrous temporal bone, close to CN VII and sympathetic innervation to the face
               ▪ Membranous labyrinth
                     Utricle, saccule – detect gravity and linear acceleration
                     Semicircular canals – detect head rotation
               ▪ Vestibular portion of CN VIII
          o Central components – at the level of the brain
               ▪ Synapses of CN VIII on vestibular nuclei and neurons at rostral cerebellum
               ▪ Connections of vestibular nuclei to:
                     CN III, IV, VI via medial longitudinal fasciculus
                     Descending pathways to spinal cord
               ▪ Important local anatomy
                     Cerebellar peduncles
                     CN V motor and sensory nuclei
                     CN VII motor nuclei
                     Descending motor and ascending sensory pathways
                     Reticular activating system (RAS)

     • Clinical signs
          o Head tilt – named for the most ventral side
          o Circling, leaning, falling and rolling
          o Ataxia – may be asymmetrical, often in absence of weakness
          o Nystagmus – spontaneous, named for the fast phase
          o Strabismus – generally ventral or ventrolateral
          o "Nausea" – hypersalivation, inappetence, vomiting, seen with acute disease