Corticobulbar tract

Clinic

• It is a two-neuron white matter motor pathway connecting the motor cortex to the medullary pyramids, which are part of the brainstem's medulla oblongata (Bulbar region)
• It is primarily involved in carrying the motor function of the non-oculomotor cranial nerves.
• Corticobulbar tract is one of the pyramidal tracts, the other being the corticospinal tract.

Functions

• It is composed of the upper motor neurons of the cranial nerves.
• Muscles of face, head and neck are controlled by the corticobulbar system, which terminates on motor neurons within brainstem motor nuclei.
• This is in contrast to the corticospinal tract in which the cerebral cortex connects to spinal motor neurons, and thereby controls movement of the torso, upper and lower limbs. Fibers that end in the sensory nuclei of the brainstem are thought to enhance or inhibit sensory transmission across various sensory nuclei. This allows for the selective attention or inattention towards various stimuli.

• Corticobulbar tract innervates cranial motor nuclei bilaterally with the exception of the lower facial nuclei (which innervates facial muscles below the eyes) and the genioglossus muscle, which are innervated only unilaterally by the contralateral cortex. Among those nuclei that are bilaterally innervated a slightly stronger connection contralaterally than ipsilaterally is observed.
• Corticobulbar tract directly innervates the nuclei for cranial nerves V, VII, IX, and XII.
• Corticobulbar tract also contributes to the motor regions of cranial nerve X in the nucleus ambiguus.