The threads of the part of the facial nucleus that controls the musculature of the lower half of the face emanate from the motor cortex of the opposite side. The motor neuron to the musculature within the upper half of the face is thought to be controlled by the motor cortex on both sides.
An injury to the tr. cortico-nuclearis on one side produces a paralysis of the facial muscles on the opposite side, counting from a line some distance below the eye; so-called central facial (facialis) paralysis.