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Dr. P here.

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I want to take you through an actual FLAIR

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thin section T1 and fast SPIN echo T2,

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describing for you the nuclear anatomy and position

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of the trigeminal system,

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as it relates to the brainstem

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and the brainstem parenchyma.

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So, I have intentionally begun at the level

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where you can see the portio major

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of the trigeminal nerve.

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There is Meckel's cave to which it will go.

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You can see the portio minor,

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the motor component going toward Meckel's cave.

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And Meckel's cave is going to sit a little bit

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more anterosuperior,

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and then as the nerve to come back,

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they come back a little bit more posteroinferior

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with only a slight obliquity.

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There's the apparent origin of the portio major,

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the sensory component of the trigeminal nerve.

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Now, let's show you where it goes.

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I'm going to go down one cut just a little bit,

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and I'm going to go posterolateral.

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So, I'm anterolateral to the fourth ventricle,

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but I'm in the posterolateral aspect of the pons,

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relative to the midline.

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So somewhere about here,

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we're going to be in the region of the

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principal sensory nucleus of 5.

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Then immediately underneath that is going

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to be the spinal trigeminal nucleus.

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So if we were to have a coronal section

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right under this round structure,

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would be a conehead consisting of the pars oralis,

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interpolaris, and caudalis.

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And so, we'd have a synapse here in the principal

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nucleus and then one on each of these as they descend

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toward the spine, eventually reaching the nucleus

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proprius and substantia gelatinosa in the spine.

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Now, what's coming here?

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I'm going to take away my color marks for a second,

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what's coming here is the sensory division of 5.

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What about the more thin, wispy,

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more medially positioned motor division of 5,

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the portio minor.

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Where does it go?

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Well, we already showed you the sensory component.

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Let's draw that back in again.

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It's kind of right about right.

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And where are we going to find the motor,

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the principal motor nucleus?

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We're going to find it a little

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more medial to this location.

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It's also going to be smaller in size.

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And then right on top of that,

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in the coronal projection, just slightly inside it.

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So if we were to stay in the coronal projection,

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just for imagination's sake,

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here's the principal motor nucleus of 5.

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Just above that is another little conehead,

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but a lot smaller than that.

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And this is going to represent the trigeminal

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mesencephalic nucleus of 5.

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And the portio minor is going to send synapse

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fibers to the trigeminal and mesencephalic nucleus of 5,

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which is going to be over here.

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And then to the principal motor nucleus,

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which is going to be right there

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as a round ring structure.

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And then as we scroll up and down, you can just

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get an idea of where these things would exist,

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relative to the anteroposterior orientation,

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and cranio-caudal orientation,

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even in the medulla.

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And when you get down in the pons,

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you're going to be somewhat posterolateral near the

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substantia gelatinosa and the nucleus proprius.

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And right next to those,

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and right above those, actually,

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are going to be some of those descending

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fibers of sensation that we describe,

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namely the pars caudalis of the spinal sensory nucleus

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Let's move on.

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That was tough.

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Dr. P out.