Corticonuclear tract (English)

The corticonuclear tract originates from the upper motor neurons (UMN) in the regions of the primary motor cortex where the head and face is represented by the motor homunculus. The corticonuclear fibers follow a similar trajectory as the corticospinal tract, passing through the posterior limb and the genu of the internal capsule to reach the brainstem. While passing through the brainstem their trajectory changes, and the fibers go on to synapse with the motor cranial nerve nuclei of the midbrain, pons and medulla. They include the motor nuclei of facial (CN VII), trigeminal (CN V), glossopharyngeal (CN IX) and accessory (CN XI). These cranial nerve nuclei represent the lower motor neurons (LMN) that go on to innervate the muscles of the face, head and neck. The corticonuclear tract also indirectly controls the motor nuclei of oculomotor (CN III), trochlear (CN IV) and abducens (CN VI) nerves. It does so via intermediary structures such as the medial longitudinal fasciculus and reticular formation.