1. Review of The vestibular system Two classes of sensory subsystems:
3 crista: encode angular acceleration
Located in the ampulla at the terminus of each of 3 fluid-filled semi circular canals
The inertial force of the fluid provides the basis for moving hair bundles
Otolith organs: encode linear acceleration
Two types:
Utricle (Horizontal acceleration)
Saccule (vertical acceleration)
Located in the utricle
The inertial force of the otoliths provides the basis for moving hair bundles

2. In both subsystems the hair cell is used to transduce head movement information
At rest there is a continuous intermediate level of NT release
Hair cells depolarize or hyperpolarize depending direction of cilium movement
Towards kinocilium depolarized (increases NT release)
Away from kinocilium hyperpolarizes (decreases NT release)
Note that all output from the vestibular organs exit the boney labyrinth via the VIII cranial nerve (vestibular-cochlear nerve)
An interesting link:

3. The vestibular system pathways: Overview
Vestibular system output travels the VII CN splits and terminates in the brain stem:
Cerebellum (movement coordination)
Vestibular nuclei. Four nuclei:
Superior
Lateral
Medial
Inferior
Output from the vestibular nuclei project
Up ipsilaterally and contralaterally to optic motor control areas (compensatory eye movements)
Down the spinal chord in two pathways to control motor output (balance and posture control)

4. The vestibular system pathways
Location of primary and secondary brainstem nuclei
Vestibular nuclei
Project to cerebellum, PPRF and spine
Paramedian pontine reticular formation
projects to abducens
Abducens
Project to lateral rectus muscle and contralateral oculomotor nucleus
Trochlear nucleus
superior oblique muscle of the eye
Oculomotor nucleus
Several extra ocular muscles

5. Vestibular nuclei

6. Vestibulospinal projections: The lateral vestibular nucleus/spinal tract
Descends the ipsilateral spinal chord
Terminates at all levels of the spine.
Excitatory pathway activates postural muscles (proximal to spine) to correct for leftward listing.

7. Vestibulospinal projections: The medial vestibular nucleus/spinal tract
Descends ipsilateral and contralateral spinal chord but asymmetrically
Terminates in the cervical and thoracic spine.
Excitatory pathway activates postural muscles (proximal to spine) mainly in the neck.

8. Ascending projections to oculomotor nuclei
Both direct contralateral and indirect ipsilateral control of extra ocular muscles
Counters head movements to keep image stable on retina.
Damage of vestibular nerve/nuclei causes nystagmus a oscillation of horizontal eye movement.