SCIENCE 101: Cranial Nerve V, the Trigeminal

Jun 01 2011 Published by under Basic Science Posts, Neuroanatomy, Uncategorized

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.


(Source)

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.

9 responses so far

  • NW Doc says:

    Scicurious: you are magnificient! Your genius is matched only by your bloggerific wit. Where were you when I was in Med School trying to learn this stuff?

  • Bethistopheles says:

    The trigeminal nerve is my mortal enemy. It ruins my days, nights, leisure time, and employment.

    The pain from this stupid nerve extends from where a migraine normally hurts (jaw, face, temple, etc.) down through the front, side, and back of my neck, across my shoulder, and down to the bottom of my scapula (only on half my body). Drs haven't figured it out yet.

    Damn you, trigeminal nerve. Damn you to hell.

    I'm terribly sorry, but I'm just pissed off right now because I'm in pain. In addition, please excuse the min-rant to follow.

    To make matters even sweeter, all they give me is NSAIDS for the pain. Pain that is so horrible it makes someone break down into tears should not be treated with effing Ibuprofen, Naproxen, or Diclofenac.

    But noooooooo, I'm under 50 years old, so my pain doesn't matter as much as someone older. So damned sick of age discrimination for painkillers and to the DEA for making Drs so afraid of prescribing them that patients needlessly suffer in unrelenting pain.

    /mini-rant

    Thanks for your interesting and amusing posts, Sci. They sometimes make me smile when everything else is full of suck. :)

    • Aliss says:

      I also stumbled onto this post with interest because of my history of childhood Bell's Palsy (three episodes!) and trigeminal neuralgia (with some involvement of Cranial VII as well). I know, or suspect I know, of the pain whereof you speak - and it is truly horrific :(

      For me, after years of investigation, I found that the cause of this inflammation is HSV. Most people get cold sores, but I get corneal ulcers and headaches that feel like I'm being stabbed repeatedly with an ice pick, and the pain can last for two or three days at a time. Do you know where your inflammation/nerve damage comes from? If not that's a good first step to getting some kind of handle on the situation. I just kept bugging doctors and getting them to refer me to specialist after specialist til I had enough data to understand the problem. I also wound up with some nifty MRI images of the inside of my head :)

      Western allopathic medicine also failed me when it came to dealing with the pain. Not even opioids really helped - they don't really work for nerve pain - and you don't want to take those anyway because they mess up your body really badly and they're crazy addictive. I've found better relief in a bunch of bizarre alternative therapies - craniosacral manipulation, acupuncture and so forth. The direct science behind this stuff is flaky at best, but I am a firm believer in the value of the placebo effect (which IS scientific). And at the very least, stimulating the nerve in different ways changes its state, and I've made it one of my major quests in life to figure out how to manipulate it out of the pain storms.

      For example, when the pain gets really bad at night, I've found that intense direct pressure right on the pain point will give me a little relief. I use an Ace bandage to bind a small pebble tightly to my head. I know all of this stuff sounds weird and silly, but I hope it might help a little. Nerve pain is really awful and it can totally ruin your life - the biggest battle for me was to find therapies that gave me a little control in how I experience the pain. It's kind of like solving a Rubik's Cube puzzle, figuring out where I can push or stick a pin in order to change the feedback in the nerve - and of course the state of the nerve changes on a daily basis. I see that Geoffrey Bove has given you a referral - I might look up Dr. Burchiel myself.

    • strixus says:

      I am also a Trigeminal Neuralgia sufferer. You should be getting by FAR more than NSAIDS. I take Gabapentin and Lyrica, and they do an amazing job at reducing the severity and frequency of the flares. Also, I've found some opiates do an ok job with the pain, while some are horrible at it - and that the variation of what works from person to person is amazing.

      Find yourself a competent neurologist. And get help. You should not have to live with that pain. No one should.

  • Geoffrey Bove, DC, PhD says:

    Bethistopheles: Trigeminal neuralgia is frustrating, but you should have better luck with it than that. The foremost person (in the world) to contact is Kim Burchiel, MD, at OHSU. This condition is his research and practice.
    http://www.ohsu.edu/xd/health/services/providers/burchiek.cfm

  • Rosencreature says:

    Sci, you are made of awesome! I knew I appreciated my trigeminal nerve, but I didn't realize it lets me sing. That makes me no end of happy. Here, have some virtual brownies in celebration. Thank you for all you do for us, your appreciative readers.

  • Bethistopheles says:

    Thanks, Geoffrey. Unfortunately, I'm waaaaaaaaaay on the other side of the US from that Dr. Thanks for the recommendation though! :)

  • Maryn says:

    Don't forget the wet-sari scene. It's right up there with the almost-kiss as a Bollywood requirement.

  • Debster says:

    Thank you SO much for the cranial nerve series. It's really helped with my A&P class.

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