Corticonuclear

Corticonuclear, or corticobulbar, refers to the part of the motor pathway that conducts voluntary control from the cerebral cortex to the motor nuclei of the cranial nerves in the brainstem. It is part of the pyramidal system and shares a cortical origin with the corticospinal tract, but its projections target the motor nuclei of the cranial nerves rather than the spinal cord.

The fibers originate primarily in the primary motor cortex (and adjacent premotor and supplementary motor areas) and descend through the internal capsule, especially the genu, and then via the cerebral peduncles and brainstem to terminate on motor nuclei of cranial nerves III through XII. In many nuclei, corticobulbar input is bilateral, but there are exceptions where innervation is predominantly contralateral. This organization contributes to the pattern of weakness seen with corticobulbar lesions.

Functionally, the corticonuclear tract controls voluntary movements of the face, jaw, tongue, pharynx, larynx, and other associated structures. Through its connections to the motor nuclei, it participates in speech articulation, swallowing, and voluntary facial movements.

Clinically, damage to the corticonuclear pathways often produces upper motor neuron signs in the cranial nerve distribution, with patterns that reflect bilateral versus contralateral innervation. Unilateral lesions may spare some functions due to bilateral input, but can cause weakness of the contralateral lower face and tongue. More extensive bilateral lesions can lead to pseudobulbar palsy, characterized by dysarthria, dysphagia, spastic bulbar symptoms, and emotional lability.