Lab 7 - Visual System

Supranuclear Motor Pathways

The supranuclear control of convergence (initiated for near vision) and divergence (initiated for distance vision) involves the supraoculomotor area (SOA) of the midbrain. When there is a binocular disparity (a marked difference between the images falling on the two foveas), control signals are sent from cortical neurons to the SOA. Neurons in the SOA project to motor neurons controlling the medial and lateral rectus muscles. During accommodation (the near response), the medial recti contract while the lateral recti relax, directing both eyes nasally. When shifting gaze from a closer object to one further away, the medial recti relax while the lateral recti contract.

This control pathway does not include the pons horizontal gaze centers or the medial longitudinal fasciculus and damage to either (the horizontal gaze center or MLF) will not affect vergence movements but will disrupt horizontal saccades.