You know, doing a series on the Cranial Nerves can get you down sometimes. I know this thing is going to be MAD useful for everyone (and may already be useful to many of you!) when it's done. But right now, it's "blah de blah nerve goes to the herp derp nucleus located in the blort de blort and innervates the doodads...". It's all a little formulaic and can get kind of...old. And Sci don't DO old.
So I was reading all about the Trigeminal, and trying to think of a way to spice it up a little. And then it occurred to me. The trigeminal nerve and what it innervates can be ENTIRELY explained with the major plot points of a Bollywood movie.
If you don't know what Bollywood is, well you're missing out.
(Completely random time periods? Check. Highly suggestive moves without ANY KISSING EVAR? Check. Entirely random plot points? Check. Folks, we have BOLLYWOOD!)
Bollywood refers to a very specific kind of movie in the Hindi language, produced in India, and specific (often) to Mumbai. It's got some very specific themes: Wildly incongruous, high energy song and dance numbers (Bollywood movies are ALWAYS musicals), highly melodramatic plot points (an evil villain tying a girl up on the train tracks is par for the course here), and the "almost kiss" which is about the sexiest thing you can get away with when making movies in India. And Bollywood...is wildly entertaining. Seriously. If you ever want to sit back with some popcorn and some seriously entertaining movies, I totally recommend Bollywood.
But melodrama. Let's talk about melodrama. Because if there's any nerve that does drama, it's the trigeminal. Here we go.
The trigeminal nerve is the first of the complicated nerves, the ones that both sensory AND motor. Thus it not only receives sensory input from your entire face, it also controls some of the muscles there (specifically the jaw, but we'll get to that later).
The sensory part of the trigeminal receives input to three main sensory nuclei, arrayed one after the other in a line as you move down the brainstem toward the spinal cord. First up is the mesencephalic nucleus, which receives mostly information on things like stretch reflexes and proprioception, or the feeling of where you are in space. It's located above the pons, and along one side of the cerebral aqueduct.
As you move down the brain through the pons and toward the spinal cord, you hit the main sensory nucleus of V, which is the main spinal trigeminal sensory nucleus. This nucleus receives information about touch and the position of your jaw.
You can see that actually the mesencephalic nucleus is just to the inside of the main sensory nucleus there, up against the aqueduct, but that's the very tail end of it.
Finally, as you move down toward the spinal cord, you hit the spinal trigeminal nucleus, which receives information about pain and temperature. This nucleus will actually extend all the way down in to your spinal cord, but it starts out in the pons just next to the main sensory nucleus up there.
From there the fibers join together, join up, and head out on either side of the pons in a nice, thick, ropey nerve that is one of the easier questions on your neuroanatomy lab.
And here's where we get into BOLLYWOOD!!!! The trigeminal nerves from the the main sensory nucleus, spinal nucleus, and mesencephalic nucleus all join up to head out of the brain. They exit the brain on either side of the pons in a nice thick bundle.
The bundle then branches off into three main sensory nerves for the face.
1) To the bottom of the face goes the mandibular division, which received input (remember this is all sensory) from the jaw, chin, and bottom of the mouth, where it receives tactile information as well as proporioception (how near something is). When the star crossed Bollywood lovers meet secretly, he runs a gentle hand down the side of her face, and they "almost kiss", he is focusing most tenderly on the mandibular division on her trigeminal. That lucky little mandibular division! The information on his closeness and the feel of his touch with go to the main sensory nucleus of V.
(The best example of the "almost kiss". Also I just think this video is hilarious.)
2) To the middle of the face gets the maxillary division of the trigeminal, which gets pain, temperature, tactile, and proprioceptive signals from the lower part of the nose, the upper lip, the cheeks, and the area right next to your eye. NOW the poor Bollywood maiden has been CAPTURED by the EVIL VILLAIN, and he is cackling evilly while he runs a bloody knife by her wide, doe-like eyes. Due to her maxillary division of the trigeminal nerve she can feel this, and well as feel his hot, fetid breath as he cackles in her ear. The information on the heat of his breath on her face will head to her spinal trigeminal nucleus, while the touch of the knife will go to the main sensory nucleus of V.
(And THEN he ties her to the train tracks. Cause that's what you DO when you're an evil villain)
3) The final sensory nerves division of the trigeminal is the ophthalamic, which gets touch, temperature, pain, etc, from the rest of the nose, the eyes, and the forehead. Our plucky, often poverty-stricken young hero (who will probably end up having a spontaneous principality thrust upon him in the end) rescues the distressed maiden! He then proceeds to give the evil villain what he deserves, which is somehow, ALWAYS, a punch in the nose.
(Unless you get away by having your horse slide sideways under a tractor trailer. You know, like you do)
Due to the sensory input from his ophthalamic branch of the trigeminal, that evil villain is going to really FEEL that punch to the nose. The information about the massive pain he is in will go straight to his spinal trigeminal, and any further punches which mess up his jaw position but good will head to the main sensory nucleus.
All seems well, plucky hero recovers maiden, and wants to declare how very delectable he finds her. But HOW will he DO THIS?!
Luckily for him, and for us all, the trigeminal has a MOTOR component. Remember how I said that the trigeminal is a nerve that has both sensory and motor? There is also ANOTHER nucleus for the trigeminal, the trigeminal motor nucleus. It's located VERY far back in the brainstem at the caudal medulla.
But the nerves from the trigeminal motor nucleus will not join up with the main trigeminal. Instead they leave the pons and join up with the sensory fibers from the mandibular division of the trigeminal, and provide motor movement to the masseter muscle, which controls the jaw, allowing us to chew. And SING!
(aaaaand, DANCE BREAK!!! This Dance Break not controlled by the trigeminal)
I hope you all have enjoyed this brief foray into the trigeminal (and into Bollywood!). And the next time you feel your jaw is tense, someone punches you in the nose, you chew gum, or someone tenderly caresses your cheek, think fondly of your trigeminal. It gets a lot done.