Glossopharyngeal nerve
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The glossopharyngeal nerve is the ninth of twelve cranial nerves. It exits the brainstem out from the sides of the upper medulla, just rostral (closer to the nose) to the vagus nerve.
There are a number of functions of the glossopharyngeal nerve:
- It receives sensory fibres from the posterior 2/3 of the tongue, the tonsils, the pharynx, the middle ear and the carotid body.
- It supplies parasympathetic fibres to the parotid gland via the otic ganglion.
- It also supplies motor fibres to stylopharyngeus muscle and the upper pharyngeal muscles.
Brainstem connections
The glossopharyngeal nerve, being mostly sensory, does not have a nucleus of its own. Instead it must project into many different structures in the brainstem.
Taste from the back of the tongue, and information from the carotid bodies enter the nucleus of tractus solitarius. Visceral pain goes to the spinal nucleus of the trigeminal nerve.
The neurons for the single muscle (stylopharyngeus) supplied by nerve IX are in the nucleus ambiguus.
Testing the glossopharyngeal nerve
The gag reflex is absent in patients with damage to the glossopharyngeus nerve.