Vestibular Anatomy

Semicircular canals
1. Monitors head rotation and spatial positioning
2. Three semicircular canals, one for each direction (X,Y and Z access)
Otolithic organs
1. Utricle
  1. Contains otoliths (small stones) that settle with position changes
  2. Detects horizontal linear movement and Head Tilting
2. Sacule
  1. Smaller, more globular organ without utricle communication
  2. Detects vertical linear movement (e.g. gravity)

Cranial Nerve VIII (2 tracts)
1. Vestibular tract carries signals from the utricle and sacule
2. Cochlear tract carries signals from the hearing apparatus in the Cochlea
Vestibular nucleii
1. Located in the pons and Medulla and receive input from the respective tracts of Cranial Nerve VIII
2. Transmit signals to the rest of the Cerebrum, Cerebellum and spinal cord to combine with other inputs (e.g. occiptal lobe, dorsal columns)
Medial Longitudinal Fasciculus and Oculomotor Nucleus
1. Brainstem fiber tracts that connect with the Oculomotor Nucleus and carry information directing eye movement
2. Connects with CN 3, CN 4, and CN 6 for eye motor activity, as well as CN 8 for head position input related to eye saccades

See Vertebro-Basilar CVA
Posterior Circulation via the vertebrobasilar system
Vertebral arteries
1. Two arteries ascend in parallel from the subclavian artery via each transverse foramen and join to form the Basilar Artery
2. Branches
  1. Posterior Inferior Cerebellar Artery (see PICA CVA)
  2. Anterior Spinal Artery
Basilar Artery
1. Arises from the joining of the two Vertebral arteries and coursing anteriorly to join with the Anterior Circulation via the Circle of Willis
2. Branches
  1. Anterior Inferior Cerebellar Artery
  2. Superior Cerebellar Artery