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Welcome to 2-minute neuroscience, where I explain neuroscience topics in 2 minutes or
less. In this installment, I will discuss the glossopharyngeal nerve.
The glossopharyngeal nerve is associated with the tongue and the pharynx, or throat, and
has both sensory and motor functions. It carries sensory information about touch, pain, and
temperature from the posterior third of the tongue, the upper part of the throat, the
tonsils, part of the outer ear, the inner surface of the eardrum, and the eustachian
tube. It also conveys sensory information from the carotid body and carotid sinus, structures
that detect oxygen, carbon dioxide, and pH levels in the blood along with changes in
blood pressure. The nerve also conveys taste information from the posterior ⅓ of the
tongue and carries motor signals to the stylopharyngeus muscle, which plays a role in swallowing and
speech. And it innervates the parotid gland, the largest of our salivary glands.
The glossopharyngeal nerve is associated with a number of nuclei in the medulla. The fibers
that supply the stylopharyngeus muscle originate in the nucleus ambiguus. The sensory fibers
that carry taste information, and those that carry sensory information from the carotid
body and carotid sinus, synapse in the nucleus solitarius, and the fibers that convey touch
and pain synapse in the spinal trigeminal nucleus. The fibers that innervate the parotid
gland arise from the inferior salivatory nucleus.
Damage to the glossopharyngeal nerve can cause a variety of symptoms, including a loss of
taste on the posterior ⅓ of the tongue, trouble swallowing, and generally decreased
sensation on the back of the tongue, the soft palate, and pharynx. Patients may also have
a diminished gag reflex, and the uvula will often deviate to the side opposite from where
the damage has occurred. In rare cases, patients may experience glossopharyngeal neuralgia,
which involves brief but intense pain in the tongue and throat.