Twelve pairs of cranial nerves mediate the transmission of afferent and efferent fibres between the brain and peripheral structures of the head and neck. Each cranial nerve is individually named and accredited a specific roman numeral according to the order, from anterior to posterior, they emerge from the brain. An overview of the function of each cranial nerve is highlighted in figure 1.
Principally, for the purpose of this resource, the anatomy of CN III, CN VII and CN IX will be considered in light of the exploration of their parasympathetic components in future sections.
CN IX: Glossopharyngeal NerveCN IX is a predominantly sensory cranial nerve, although it also contains preganglionic parasympathetic fibres and motor fibres to one nerve, the stylopharyngeus muscle. Axons originate laterally within the anterior medulla and pass out through the jugular foramen into the oral cavity and auditory canal.
Afferent fibres carrying sensory information from the nasopharynx, oropharynx, adenoid, palatine tonsil, auditory tube and middle ear terminate within the trigeminal nucleus, with afferent fibres carrying special taste sensation for the posterior one-third of the tongue terminating in the nucleus solitarius. Efferent fibres innervating stylopharyngeus arise from the nucleus ambiguus of the medulla. Parasympathetic innervation is covered in more detail in the following section. |