Wednesday, October 12, 2016

Deviation of the tongue, jaw, uvula and lips in cranial nerve palsy mnemonic

Hello! Long time no see (From my side :D )

So in this post, I'll be taking about what deviates where with a mnemonic! Yaay!
What? Jaw, tongue, lips and uvula.

Let's start with LMN lesions of the respective cranial nerves.

Hypoglossal, the 12th cranial nerve and tongue deviation:
Infranuclear injuries of the hypoglossal nerve will cause deviation of the tongue towards the affected side when it is stuck out.
Wanna understand why? The muscles of the tongue keep the tongue in midline by pushing towards the opposite side. If one side is atrophies, the other side muscles are stronger and push the tongue to the side of the lesion.)
Mnemonic: The tongue licks it's wounds. (Licks - deviates, wounds - affected side.)

Trigeminal, the 5th cranial nerve and jaw deviation:
 Injury to the peripheral part of the mandibular nerve can cause paralysis of muscles on one side of the jaw, with the jaw deviating towards the paralyzed side when it opens.
Wanna understand why? The lateral pterygoid muscles (along with some of the upper neck muscles) open the jaw in concert with a downward and opposing inward motion. When one lateral pterygoid is weak, the jaw deviates toward the weak side on opening, with the inward vector of the opposite pterygoid being unopposed.

Vagus, the 10th cranial nerve and uvula deviation:
The uvula deviates away from the side of the lesion in a patient with lesion of the vagus nerve.
Wanna understand why? Normal palatal arches will constrict and elevate, and the uvula will remain in the midline as it is elevated. With paralysis there is no elevation or constriction of the affected side. The uvula deviates away from the side of the lesion because there is failure of palate elevation.

Facial, the 7th cranial nerve and lips deviation:
Th lips deviate away from the side of the lesion in a patient with LMN type of 7th nerve palsy.
Wanna understand why? The facial nerve makes you smile. If the affected side doesn't work, when you smile, lips will be pulled to the opposite side.

MNEMONIC ^___^
So now you know that tongue (12) and jaw (5) deviate to the affected side, lips (7) and uvula (10) towards the opposite side. You also know the tongue (12) licks it's wounds.

Now you simply have to remember the magic number 17!
12 + 5 = 17 (Deviates to the same affected side)
10  + 7 = 17 (Deviates to opposite to the affected side)

Deviation of the tongue, jaw, uvula and lips in cranial nerve palsy mnemonic
Here's another mnemonic for remembering whether muscles push the tongue and jaw towards the midline or pull away the uvula or lips. Write 5, 7, 10, 12 in numerical order and then the outer numbers push in, the inner numbers pull away!

Deviation of the tongue, jaw, uvula and lips in cranial nerve palsy mnemonic
Ta-da!

Hope that simplifies things :)
I'll be sharing on UMN lesions on a later day.
Till then, take care!

-IkaN

Credits:
Sakkan for the 17 mnemonic. Thanks for sharing this on the study group!
Huzaifa for sharing Suraj Bhame's push and pull mnemonic.

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