The Indirect Path of the VOR

Where does the required tonic input come from?

The tonic command originates via the indirect path through the n. prepositus hypoglossi

This nucleus converts the phasic vestibular input into a tonic signal (in the same way as it does for the phasic command of saccades).

Motoneurons thus normally exhibit the combined input from:
1) a phasic command (which rotates the eye) via the direct path
2) a tonic command (which holds it there) via the indirect path

Copyright © 1996 Tutis Vilis and Douglas Tweed
University of Western Ontario
London Ontario Canada
Updated October 28, 2005

Comments welcome. Email to tutis.vilis@schulich.uwo.ca