Direct path of the VOR is a short tri-synaptic reflex
consisting of 1) vestibular n.(vn), 2) motoneurons (in the VI and III nuclei),
and 3) muscles (lateral rectus, lr, and medial rectus, mr).
The direct path, by itself, is not enough. Why?
During the head rotation there is a phasic response seen in vestibular
afferents (sense how fast you rotate), which rotates the eyes to
the left.
After the head rotation this phasic activity stops.
This presents a problem: the eye would drift back to center because the
muscles need a tonic input to keep the eye rotated. |
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