Figure 3 Projections involved in the activation of the left anterior canal

Axons from anterior semicircular canal neurons project to the ipsilateral vestibular nucleus and from there decussate across the brainstem to innervate the contralateral inferior oblique nucleus of cranial nerve III (and then the muscle itself) and the ipsilateral superior rectus muscle via a second decussation from the superior rectus subnucleus on the right, which completely crosses back to the left (on the right side of the figure). The excitatory pathways are shown in orange and the reciprocal inhibitory pathways are shown in blue. Activation of both canals (as with pitching the head downward and attempting straight ahead fixation) will result in cancellation of the torsional vector components, but addition of the vertical vector components resulting in upward movement of the eyes.