Glossopharyngeal nerve

Special sensory function

Mediates taste from the posterior 1/3 of the tongue.

Sensory function

Provides sensory innervation to the middle ear, posterior 1/3 of tongue and pharynx.

Motor function

Innervates stylopharyngeus muscle.

Visceral functions

• Supplies parasympathetic efferents to parotid gland.
• Mediates parasympathetic afferents from the carotid body and sinus.

Anatomy

1. Intra-axial segment

All glossopharyngeal associated nuclear complexes are in the upper and middle medulla oblongata.

Motor fibers to stylopharyngeus muscle originate in nucleus ambiguus.

Sensory fibers from the tympanic membrane, soft palate, posterior 1/3 of tongue and pharynx terminate in thespinal nucleus of trigeminus.

Taste fibers from the posterior 1/3 of the tongue terminate in the tractus solitarius nucleus.

Parasympathetic fibers to parotid gland arise in the inferior salivatory nucleus.

2. Cisternal segment

Emerges laterally from the medulla in the postolivary sulcus, above the origin of vagus nerve. It courses through the basal cisternae together with vagus and the bulbar portion of accessory nerve. Passes through glossopharyngeal meatus into pars nervosa of the jugular foramen.

3. Skull base segment

Courses anteriorly in pars nervosa of jugular foramen. Vagus and spinal accessory nerves course posteriorly within pars vascularis of jugular foramen.

Within the jugular foramen are also located the superior and inferior sensory ganglia of glossopharyngeus.

3. Extracranial segment

Distal to the jugular foramen it courses within the anterior carotid space, lateral to the internal carotid artery and stylopharyngeus muscle and terminates in the posterior sublingual space in the floor of the mouth.

Extracranial branches

The tympanic branch (Jacobsen’s nerve) originates from the inferior sensory ganglion in the jugular foramen. It passes through inferior tympanic canaliculus into the middle ear. It contains sensory fibers from the middle ear and parasympathetic efferents to parotid gland.

The stylopharyngeus branch innervates stylopharyngeus muscle.

The sinus nerve carries visceral sensory fibers mediating impulses from stretch receptors and chemoreceptors from carotid sinus and carotid body respectively.

The pharyngeal branches carry sensory fibers from the posterior oropharynx and soft palate.

The lingual branch carries sensory and taste fibers from the posterior 1/3 of the tongue

Clinical implications

• Damage to glossopharyngeal nerve results in loss of taste sensation, abnormal gag reflex and difficulty in swallowing.
• Glossopharyngeal dysfunction is almost never isolated. It usually is associated with dysfunction of vagus and accessory nerves.
• Glossopharyngeal neuralgia is more common in middle-aged males. Often no cause is identified. Sometimes may be caused by neurovascular conflict.
• Rare causes of isolated glossopharyngeal palsy include compression by tumor, infection, stroke and compression by rheumatoid panus affecting the atlantoaxial joint or processes affecting the jugular foramen.