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The glossopharyngeal nerve is a mixed ninth cranial nerve: it carries pharyngeal and lingual sensation, posterior tongue taste, carotid sensory input, motor fibres to stylopharyngeus, and a secretomotor route to the parotid gland. Its connections explain why its name alone understates its functions.

Rootlets leave the lateral medulla oblongata, behind the olive and above those of the vagus nerve. They cross the posterior cranial fossa and leave through the jugular foramen. Superior and inferior sensory ganglia lie at or near that passage. The cervical trunk descends in relation to the internal carotid artery and internal jugular vein, then turns forwards around stylopharyngeus. It reaches the pharyngeal wall between the superior and middle constrictors and divides towards the posterior tongue, tonsillar region and pharynx. Its topographical association with the vagus does not make the two nerves functionally identical.

The tympanic branch returns through the inferior tympanic canaliculus into the middle ear. Its tympanic plexus supplies the mucosa of the tympanic cavity, auditory tube and related air spaces and communicates with carotid sympathetic fibres. Preganglionic parasympathetic fibres continue through the lesser petrosal nerve to the otic ganglion. Postganglionic fibres then reach the parotid gland with the auriculotemporal nerve, a branch of the mandibular division of the trigeminal nerve. This is a useful example of fibres originating in one cranial outflow and travelling for their last segment with another nerve.^[ref]

The branch to stylopharyngeus is motor; contraction elevates and expands the pharynx during swallowing. Pharyngeal branches contribute to the pharyngeal plexus, together with the vagus nerve and sympathetic connections. The principal motor supply of the pharyngeal constrictors is vagal: membership of a mixed plexus does not justify assigning every fibre or every pharyngeal muscle to the ninth nerve. Tonsillar branches supply the palatine tonsil and neighbouring mucosa. Lingual branches carry ordinary sensation and taste from the posterior third of the tongue, including the vallate papillae even though these lie just anterior to the terminal groove.

The carotid sinus nerve carries information from pressure-sensitive endings in the carotid sinus and from the carotid body's chemical sensors. The first contributes to regulation of blood pressure; the second responds especially to arterial oxygen deficiency, with responses also influenced by carbon dioxide and acidity. These are afferent functions, distinct from the motor and secretory branches.^[ref]

In the modern central account, branchial motor fibres arise from the nucleus ambiguus, parasympathetic fibres from the inferior salivatory nucleus, visceral and taste afferents project towards the solitary nucleus, and relevant general sensory fibres project to the spinal trigeminal system. These nuclear and reflex distinctions refine the gross anatomical description available in 1864. Pharyngeal touch can initiate swallowing and contributes to the afferent limb of the gag reflex, whose principal motor limb is vagal. Ordinary sensation, taste, pharyngeal movement and secretion therefore need separate observations; the absence of one response does not by itself prove loss of every ninth-nerve function.^[ref]