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I hope you’re like soooo good with the trigeminal and facial nerves now.
Today’s topic is the the glossopharyngeal nerve. The glossopharyngeal nerve is cranial nerve 9, nine, nueve, IX!! CN IX has more sensory responsibilities than motor, but does have key motor innervation as well.
The glossopharyngeal nerve provides:
1. Sensation in ALL forms including TASTE from the POSTERIOR 1/3 of the tongue. (Remember that the facial nerve is responsible for taste to the anterior 2/3).
2. Somatosensation (meaning touch, pain and temperature) from the mucosa of the soft palate AND upper pharyngeal mucosa
3. A parasympathetic portion of CN IX Innervates the parotid salivary glands to aid in wetting and forming a cohesive bolus.
It has been widely discussed in the field that assessing the gag reflex will provide input regarding CN IX, however this is NOT the case. The sensory portion of the gag reflex, which is a bit more forward from the PPW can be elicited via CN V, and the motor part of the gag reflex is all CN X (pharyngeal wall medialization, velar elevation, which we haven’t discussed yet). So the antiquated practices of stroking the faucial pillars or placing a lemon swab at the back of the tongue doesn’t really tell you squat about CN IX.
CN IX only provides MOTOR innvervation to the:
- Stylopharyngeus, which is also a laryngeal elevator (because it lifts the entire pharyngeal wall up) which also assists in relaxing and opening of the cricopharyngeus.
If you do know that the patient has damage to the motor fibers of CN IX, the patient may have difficulty moving food through the pharynx due to weak pharyngeal constrictor contraction, possibly leading to failure of opening of the UES/PES.
What’s extremely important to remember here is that there is no way to reliably assess CN IX at the bedside, as there is an extremely high risk of false positives. So those cranial nerve exams at the bedside that you haven’t been doing anyways? Well, you’re in luck, you’re off the hook with the glossopharyngeal, since you cant assess jack squat clinically at the bedside anyways for this guy.
So in conclusion, CN IX is responsible for sensory input from the posterior 1/3 of the tongue (including taste), mucosa of the soft palate, upper pharyngeal mucosa, and the parotid salivary gland, AND motor innervation to the stylopharyngeus.
Resources: (And a special thank you to Dr. Kate Krival for verifying that I might know what I’m talking about
Corbin-Lewis, K, Liss, J.M., & Sciortino, K.L., 2005, Clinical Anatomy & Physiology of the Swallow Mechanism, Thomson Delmar Learning, Clifton Park, NY
Murray, J., 1999, Manual of Dysphagia Assessment in Adults, Singular Publishing Group, Inc., San Diego
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