Corticobulbar tract

Clinic

• It is a two-neuron white matter motor pathway connecting the motor cortex to the medullary pyramids
• Medullary pyramids 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 upper motor neurons of cranial nerves.
• It terminates on motor neurons within brainstem motor nuclei and control muscles of face, head and neck.
• This is in contrast to 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.

• It innervates cranial motor nuclei bilaterally with the exception of
  • The lower facial nuclei (which innervates facial muscles below the eyes)
  • 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.

	Bilateral			Unilateral
	Trigeminal N.	Glossopharyngeal N.	Vagus N.	Facial N.	Hypoglossal N.
Entities		Dysarthria Dysphagia		Bel's palsy	Dysarthria
Diseases					Pseudobulbar palsy
Miasms		NVCJD CJD FFI

• It originates in Primary motor cortex and follows a similar path to the corticospinal tract.
• Its fibers bilaterally innervate almost all cranial nerve except for cranial nerves VII and XII, which are innervated by the contralateral cortex.
• Therefore corticobulbar tract lesion on the left side of the face will cause weakness of the right side.
• Since every other cranial nerve except for VII and XII are innervated bilaterally, lesions to both sides of the corticobulbar tract will need to occur for symptoms to appear.
• Damage to the corticobulbar tract can present with pseudobulbar palsy or damage to cranial nerves VII or X.
• Damage to CN-VII will cause deviation of angle of mouth towards the opposite side of the lesion due to the overaction of the muscles of the opposite side.
• Damage to CN-X will lead to the deviation of the uvula to the opposite side of the lesion.