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I hope you learned a little suttin’ suttin’ from reading Part 1 – the Trigeminal nerve! (Go check it out if you didn’t, it explains why I feel this stuff is so dang important) I received some great feedback from the last post that people really enjoy the simplicity of my writing, and I think thats exactly it! I’ve been studying this stuff for years, and it never really sunk in until I dumbed it down enough in to normal people language instead of the fancy medical shit. I’ve since been able to explain it better to others and actually integrate it into what I’m seeing at the bedside (what a novel idea!!!)
Today, I’m on to the Facial Nerve. Cranial nerve 7, seven, siete, the big VII!! The facial nerve does not have a gigantic role in the actual swallow, but is responsible for a large portion of the oral phase and.. TASTE! Which is hella important in my book!
Now, we learned in the last post that you’d probably think that the facial nerve would cover sensation to the welp.. FACE, but alas, trigeminal took the cake for that one!
But, the facial nerve DOES control…
1. MOTOR output to the face, including several muscles of facial expression, oral acceptance (i.e. orbiculoris oris), and pocketing prevention (buccinator).
2. Innervation to the stylohyoid and posterior belly of the digastric. Although they are considered hyoid elevators, they elevate and RETRACT the hyoid, so they aren’t nearly as important as the muscles that protract the hyoid and give us hyolaryngeal excursion.
3. Taste from the ANTERIOR 2/3 of the tongue, so anything (i.e. lemon swab, sugar, salt) you place on the oral tongue (all the way back to the huge circumvallate papillae) will all be assessing the facial nerve.
4. Submandibular and sublingual salivary glands – The facial nerve has a separate component that sends autonomic motor innervation to these glands so if we have a patient presenting with a dry mouth, we know the facial nerve may be in play.
The facial nerve is relatively easy to assess in that you can often look at the patient and notice a facial droop to one side or the other, if you see that you instantly know that the patient has facial nerve involvement and to which side. Not to get to crazy scientific here, but the facial nerve (Just for the face, below the eye) is 1 of 2 (along with the hypoglossal) that only receives innervation from 1 side of the brain, the contralateral side (the opposite side). So if you’re suspecting an upper motor neuron lesion, the lower side of the face on the opposite side (contralateral) will be affected. If you have a lower motor neuron lesion, both the upper and lower sides of the face on the same side (ipsilateral) as the lesion will be affected. (This is just a good little tidbit of info to keep in your cranial nerve assessment back pocket.)
Other tasks to assess the motor portion of the facial nerve include having the patient pretend to blow out some candles (orbicularis oris), and puff out their cheeks (buccinator), important for oral acceptance and the prevention of anterior spillage and pocketing, respectively. (Side note: I just cant get on board with the term “squirreling”, “pocketing” is bad enough but “squirreling” is downright weird. I’m not sure I want to see that I “squirrel” in my medical chart when I’m older but maybe that’s just me.)
Therefore, If you see George in the dining hall constantly using his finger to pluck all of that tuna fish out of his cheeks, chances are he’s having some difficulty with that buccinator muscle and CN VII. Additionally, if George just cant seem to keep that chicken noodle soup shoveled in and its constantly splashing back in to the bowl.. Ditto! CN VII! Wake up orbiculoris oris! Our friend George may also have some difficulty wetting and forming a bolus due to decreased salivary gland production.
Some possible treatment strategies to improve these deficits may be exercises to the lingual, labial, or mandibular musculature, IOPI, or NMES in the facial placement, just to name a few.
In conclusion, the facial nerve is responsible for taste (anterior 2/3), submandibular and sublingual salivary glands, motor movement of the face (orbicularis oris and buccinator) as well as the stylohyoid and PBD. Therefore, if you have a patient presenting with any of these deficits, you know that the facial nerve is in play. Again, not crazy important for the pharyngeal swallow, but taste and the oral stage of the swallow are pretty dang important too!
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