Figure 4 Projections from the left posterior semicircular canal

Axons from the canal project to the ipsilateral vestibular nuclei and then decussate to innervate the contralateral inferior rectus subnucleus of the oculomotor complex of cranial nerve III and the trochlear nucleus. The trochlear neurons then exit the brainstem posteriorly and decussate back to the left side innervating the superior oblique muscle. Activation of both canals (as with pitching the head upward and attempting straight ahead fixation) will result in cancellation of the torsional vector components, but addition of the vertical vector components resulting in downward movement of the eyes.