Stylopharyngeus and the glossopharyngeal nerve
Stylopharyngeus, a throat muscle, comes from the third pharyngeal arch (a bar of embryonic tissue) and is supplied by that arch's nerve, the glossopharyngeal nerve (cranial nerve IX).
Remember
Stylopharyngeus is the exception in the pharynx: the third arch is paired with cranial nerve IX, whereas most other pharyngeal muscles are supplied by the vagus nerve (cranial nerve X, the nerve of the fourth and sixth arches).
Each pharyngeal arch is paired with a cranial nerve, and the muscles that develop from the arch keep that nerve. The first arch goes with the trigeminal nerve (cranial nerve V) and gives the muscles of mastication (chewing). The second goes with the facial nerve (cranial nerve VII) and gives the muscles of facial expression. The third pharyngeal arch is paired with the glossopharyngeal nerve (cranial nerve IX).
The third arch gives rise to stylopharyngeus. This muscle runs from the styloid process (a slender bony spike below the skull) to the wall of the pharynx, and it helps shorten and widen the pharynx and lift the larynx (the voice box) during swallowing. It is the only muscle in the pharynx supplied by the glossopharyngeal nerve.
Most other muscles of the pharynx, including the constrictors (the muscles that squeeze food down the throat), are supplied by the vagus nerve (cranial nerve X), the nerve of the fourth and sixth arches. That is why stylopharyngeus is the exception.
An isolated injury to the glossopharyngeal nerve weakens stylopharyngeus, so lifting the pharynx and larynx in swallowing is weaker. Other muscles also help to raise the pharynx, so expect a weaker contribution to swallowing rather than a complete loss. The nerve also gives both taste and general sensation to the back of the tongue (its posterior third). In the gag reflex (a two-part pathway, or reflex arc), it carries the signal from the back of the throat towards the brainstem, while the vagus nerve carries the response back to the muscles that contract.
Key facts
- Arch and nerve
- the third pharyngeal arch is paired with the glossopharyngeal nerve (cranial nerve IX)
- Arch pairings
- arches one, two and three go with cranial nerves V, VII and IX, and the fourth and sixth arches go with the vagus nerve (X)
- Action
- stylopharyngeus helps shorten and widen the pharynx and lift the larynx during swallowing
- The exception
- stylopharyngeus is the only muscle in the pharynx supplied by the glossopharyngeal nerve, while most others use the vagus nerve
- Also from cranial nerve IX
- both taste and general sensation, from the back of the tongue (its posterior third)
- Gag reflex
- cranial nerve IX brings the sensation in and cranial nerve X carries the response out
Exam traps
- The vagus nerve is the tempting choice for a swallowing problem, because it supplies most of the muscles of the pharynx, but stylopharyngeus is the exception and takes its supply from the glossopharyngeal nerve.
- The first arch is a tempting guess because chewing and swallowing follow each other in eating, but it forms the muscles of mastication, supplied by the trigeminal nerve, while stylopharyngeus has glossopharyngeal supply.
- The middle pharyngeal constrictor takes part in swallowing, but as one of the circular muscles of the pharyngeal wall it squeezes the pharynx rather than lifting it.
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