The VOR is a very simple central reflex. The
sensory input is head velocity and the motor
output is eye velocity. The head velocity signal
is transmitted from the semicircular canals to
the vestibular nucleus via primary vestibular
afferent fibres in the eighth cranial nerve.
Second order vestibular nuclei project to the
appropriate pools of extraocular muscle
motoneurons.
Thus in its simplest form, the VOR is referred
to as a three-neuron-arc:
1) Primary vestibular afferent
2) second order vestibular interneuron
3) extraocular muscle motoneuron.
For the horizontal reflex, head velocity
information form the horizontal canals is sent to
vestibular interneurons in the medial vestibular
nucleus. The vestibular interneurons project to
abducens nucleus and contact the lateral rectus
muscle motoneurons and a population of
internuclear neurons that in turn project tot he
contralateral pool of medial rectus motoneurons
to maintain conjugacy.
