Anatomy and Physiology of Balance by HC120104164428

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									Anatomy and
Physiology of
  Balance
  Vestibular Hair Cells
• Type I
  (aka inner)
• Type II
  (aka outer)

     With
   Kinocilium
        The Semicircular Canals
• posterior canal
  shares plane with
  contralateral
  anterior canal.

• horizontal canals
  share plane.
  Stimulated by Angular Acceleration

• greatest when fulcrum
  is within head

• induces relative motion
  of endolymph

• crista is displaced by
  fluid motion
          Responses of the Cristae

• All kinocilia are
  oriented in the
  same direction

• Crista in each pair
  of canals respond
  inversely to each
  other
     The
   Otolithic
   Organs

Saccule: roughly
vertical orientation,
responds to acceleration components within saggital
  plane

Utricle: horizontal (+ 30 deg.) orientation
Excitation Patterns in the Utricle

                           STRIOLA

                              Anterior




Posterior
                            Medial
Cranial Nerve VIII
   Vestibular Portion of C.N. VIII
superior division: utricle, anterior part of
  saccule, and horiz & anterior canals
inferior division: posterior part of saccule,
  and posterior canal
• to vestibular nuclei
• to cerebellum
          Vestibulocochlear Nerve

• Exits temporal bone
  near its medial edge.

• Enters lateral face of
  brainstem at the level
  of the lower pons.
• Synapsing in
  (Cochlear and)
  Vestibular Nuclei
Responses of Vestibular Neurons:


• To changes in acceleration, but onset
  and fade slowly

• For most normal head movements
  firing rates are in phase with head
  VELOCITY.
Other inputs to vestibular nuclei:

•   Cerebellum: primarily inhibitory
•   Spinal cord
•   Pontine reticular formation
•   Contralateral vestibular nuclei
       From the Vestibular Nuclei:
• Vestibulo-Oculomotor Pathways:
  – Direct: to oculomotor nuclei.
  – Indirect: via reticular formation to
    oculomotor nuclei (III IV and VI)
• Vestibulo-Spinal Pathways:
  – Lateral V-S-throughout spinal cord
  – Medial V-S-cervical & thoracic
  – Reticulospinal tract-via brainstem reticular
    formation
  Median Longitudinal Fasciculus
• A tract linking Vest. Nuclei to
  nuclei of CN III, IV, & VI;

• Supports conjugate eye
  movement during movement of
  the head.

• Continuous with the medial
  vestibulospinal tract.

• The mlf runs near midline
  ventral to ventricle IV and the
  periaqueductal gray matter of
  the midbrain
           In the brainstem
• Vestibular inputs undergo integration
• Integrated signal is combined with
  original (velocity driven) signal
• Processing to reset spatial map for eye
  musculature
Integration & ―Leaky‖ Integration
The VOR
Central Nervous System Will
Adapt to Peripheral Damage
             Eye Movements

• Saccades—rapid shift in gaze
• Pursuit—stabilize image of moving object
• Fixation—stabilize image of still object
• VOR—stabilize image during head motion
• OKN—backup for when VOR decays to
  cont’d head rotation
• Vergent movements—change depth of focus
Saccades
Pause cells inhibit
Burst Neurons
 which stimulate:
III & VI (horizontal)




 or
III & IV (vertical)
     Compare, Select
    & Combine Senses


Visual   Vestibular   Somato-
System    System      Sensation




SENSORY INPUTS
     Vision
    Vestibular
  Somatosensory
SOMATOSENSORY
RECEPTORS Compare, Select
                & Combine Senses

                                   Somato-
                                   Sensation


                        Joints
                       Position
                      Kinesthesia

                      Muscles
                        Length
                        Tension
                         Skin
                        Touch
                       Pressure
VISUAL        Compare, Select
             & Combine Senses
RECEPTORS
            Visual
            System



                     Central
                     Orientation
                     Navigation

              Peripheral
             Motion-sensitive
               Body-sway
        VESTIBULAR RECEPTORS

                      Compare, Select
                     & Combine Senses

                         Vestibular
                          System


Semi-circular canals
       Orientation
       Navigation


 Utricle & Saccule
   Horizontal & vertical
acceleration & deceleration
         SENSORY ORGANIZATION
  Determination of Body
        Position

          Compare, Select
         & Combine Senses

Visual     Vestibular   Somatosensory


    Processing of inputs from the periphery
     Selection based on
          Availability Accuracy
          Value for the task at hand
 Functional
  Balance:
Navigating in
    our
Environment
                      A Quiz
Vestibular Pathways Quiz

								
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