Corticobulbar

The corticobulbar tract, also known as the corticonuclear tract, is a motor pathway that transmits voluntary commands from the cerebral cortex to the motor nuclei of cranial nerves in the brainstem. It serves to control the muscles of the face, head, and neck, including those involved in speech and swallowing. It is considered part of the pyramidal (corticospinal) system and is closely linked to the corticospinal tract.

Originating mainly from the precentral gyrus and neighboring frontal areas, with additional input from related cortical regions, corticobulbar fibers descend through the internal capsule and brainstem. They synapse on motor nuclei of cranial nerves V, VII, IX, X, and XII in the brainstem. The pattern of innervation is predominantly bilateral for many nuclei, but some muscles show more contralateral influence, notably the lower facial muscles and the intrinsic tongue muscles.

Functionally, the tract enables voluntary control of movements necessary for facial expression, mastication, swallowing, phonation, and articulation, as well as coordination of palate and pharyngeal mechanics essential for speech and swallowing.

Clinically, lesions affecting the corticobulbar pathways—often as part of an upper motor neuron syndrome from stroke or tumor—produce signs such as spastic weakness, exaggerated reflexes, and contralateral weakness of the lower face. Because many cranial nerve nuclei receive bilateral input, some functions (such as palate and pharyngeal movements) may be relatively preserved in unilateral corticobulbar lesions, though patterns can vary with the exact site and extent of injury.