The branchial motor component of CN IX provides voluntary control of the stylopharyngeus muscle which elevates the pharynx during swallowing and speech.
Origin and Central Course
The branchial motor component originates from the nucleus ambiguus in the reticular formation of the medulla.
Fibers leaving the nucleus ambiguus travel anteriorly and laterally to exit the medulla, along with the other components of CN IX, between the olive and the inferior cerebellar peduncle.
Upon emerging from the lateral aspect of the medulla the branchial motor component joins the other components of CN IX to exit the skull via the jugular foramen.
The glossopharyngeal fibers travel just anterior to the cranial nerves X and XI which also exit the skull via the jugular foramen.
Extracranial Course and Final Innervation
Upon exiting the skull the branchial motor fibers descend deep to the styloid process and wrap around the posterior border of the stylopharyngeus muscle before innervating it.
Voluntary Control of the Stylopharyngeus Muscle
Signals for the voluntary movement of stylopharyngeus muscle originate in the pre-motor and motor cortex (in association with other cortical areas) and pass via the corticobulbar tract in the posterior limb of the internal capsule to synapse bilaterally on the ambiguus nuclei in the medulla.