Vestibular Review

Vestibular Anatomy 

  • Semicircular Canals:

    • 3 of them: anterior, posterior, horizontal 

    • Canals are oriented in pairs with a co-planar pair in the opposite ear.

    • Endolymph circulates within each canal. Movement results in deflection of the Cupula

  • Cochlea 

    • Hearing organ with connection to the vestibular system

  • Vestibulocochlear Nerve  

    • CN 8: responsible for balance, eye movements, and hearing 

  • Cupulla 

    • Ampulla is the bony enlargement that holds the cupulla 

    • Cupulla is a large flap which shifts during rotational movements 

      • Impacted by endolymph 

    • Stereocilia and Kinocilium are hairlike cells embedded in the cupula which regulate depolarization and hyperpolarization of the nerve 

      • An increase in velocity is associated with a greater magnitude of change in excitation and inhibition 

  • Otolith Organs 

    • Gelatinous membrane with embedded calcium carbonate crystals within otolithic maculae 

      • Utricle: Sensor for acceleration in the horizontal plane 

      • Saccule: Sensor for acceleration in the vertical plane 

  • Brainstem (Vestibular Nuclei) 

    • CN 8 synapses in the brainstem 

    • Vestibular nuclei in the pons and medulla with multiple central connections:

      • Cerebellum: VOR, posture control, coordination 

      • Brainstem: ocular nuclei 

      • Reticular Formation: arousal 

      • Thalamus: spatial perception 

      • Cerebral Cortex: spatial perception 

  • Cerebellum 

    • Compares vestibular, somatosensory, and visual inputs

    • Floculus maintains gain of VOR

    • Vestibular adaptation is mediated here 

    • Nodulus adjusts duration of VOR and receives otolith information 

    • Habituation is mediated here 

    • Anterior superior vermis modulates VSR 

    • Lesions here would produce ataxia of gait and trunk 

Vestibular Assessment 

  • Visual Performance 

    • Smooth Pursuit

      • Follows a moving target 

      • Requires a target (can’t do this voluntarily without one) 

    • Saccades 

      • Rapid conjugate movement to place the retina on a target 

    • Vergence 

      • Eyes move towards or away from midline (near to far) 

    • Visual Fixation 

      • Maintenance of gaze on a single location under non moving conditions 

    • VOR 

      • Maintenance of gaze on a single location while the head is moving 

      • VOR cancellation is a normal phenomenon 

      • For Fast head movements! 

  • Balance Assessment 

    • Direct vestibular function is not typically tested in PT clinics so balance testing is used in order to make conclusions. Examples include: 

      • CTSIB 

        • Balance test with 6 conditions 

      • Romberg 

        • Uses variations of EO/EC 

      • MiniBEST 

        • Sensory conditions, Dynamic conditions 

  • Somatosensory Integrity 

    • The impact of proprioception, light touch, protective sensation, and kinesthesia is important when assessing the impact of vestibular function 

  • Symptom Report 

    • Specific descriptors of dizziness, lightheadedness, imbalance, etc, can assist in the diagnostic process, A strong subjective can be the most critical component to vestibular examination 

    • Further outcomes measures to assist with symptom report include: 

      • DHI (Dizziness Handicap Inventory)

      • ABC (Activities of Balance Confidence Scale) 

      • VHQ (Vertigo Handicap Questionaire) 

      • VADL (Vestibular Disorders Activities of Daily Living Scale) 

Vestibular Function Review 

  • Semicircular Canal 

    • Rotational movement causes endolymph to circulate within the canals 

    • Cupula is impacted by the endolymph and kinocilia/stereocilia altered nerve firing rate. Change in firing rate occurs bilaterally (excitation on one side and inhibition on the other) 

    • Excitation is unlimited but because inhibition ceases at 0 pps, vestibular function is limited above head velocities of 180 degrees/sec. 

  • Otolith Organs

    • Sense linear movement in horizontal and vertical planes 

  • Pathways 

    • Medial longitudinal fasciculus and superior colliculus (Extraocular muscles) 

    • Vestibulospinal tracts 

    • Vestibulocollic pathways (influence head position) 

    • Vestibulothalamocortical pathways (conscious awareness of head movement and position) 

    • Vestibulocerebellar pathways 

    • Vestibuloautonomic pathways (to reticular formation, influencing N and V)