Anatomy of the glossopharyngeal nerve (CN IX)

The glossopharyngeal nerve is the ninth cranial nerve and it has several roles. From helping us taste a freshly picked strawberry on the back of the tongue through its special sensory role, to keeping the carotid sinus in the loop about blood pressure variations through its visceral sensory component, as well as providing branchial motor innervation to a muscle in the pharynx and parasympathetic innervation to the parotid gland.

It may also receive somatic sensory information from a tiny part of skin on the external ear, but this isn’t important to remember. This nerve is working four - sometimes five - jobs, and doing them all really well!

But now, where did the glossopharyngeal nerve come from? The glossopharyngeal nerve actually originates from a structure called the third pharyngeal arch that forms during intrauterine life, when the embryo is roughly the size of a poppy seed.

Remember that the pharyngeal arches are 6 embryological structures, of which only 5 eventually develop into the muscles, arteries, bones and cartilage of the head and neck.

Now, the third pharyngeal arch is less complex than the first two arches and gives rise to only a few structures such as the common carotid artery, the proximal portion of the internal carotid artery, the lower body and the greater horn of the hyoid bone and the stylopharyngeus muscle.

All of these structures are innervated by the nerve of the third pharyngeal arch, which is the glossopharyngeal nerve.

So let’s take a closer look at the roles of this nerve. First up, there’s the special sensory component, that picks up taste information from the taste buds located in the posterior one-third of the tongue.