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Dr. P here to talk about the 7th nerve or facial nerve.

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I'm showing you a gross diagram of the brainstem at the

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level of the pons.

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Here's the pontomedullary sulcus.

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You can see the apparent exit of the 7th nerve,

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but the real origin, this is the apparent origin.

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The real origin of the 7th nerve is in a nucleus.

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Now, what's curious is in this sagittal diagram,

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which is anatomically correct,

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the 7th nerve fibers course in the brainstem for a

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variable distance loop around the nucleus of six,

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the abducens nerve nucleus,

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and then move forward as they create the

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apparent origin of the 7th nerve.

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So, let's look at that in the axial projection on an MRI.

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So I have before you a sagittal T1, high resolution,

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thin section image on the left.

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But pay no attention to that for right now,

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I want to focus your attention on the right side

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of the screen, the axial T2 high res image.

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Here is the 6th nerve coming out anteriorly.

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But I am interested in the real origin of the 7th nerve.

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So, let's take a look at this axial view at the level of

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the brachium pontis, the middle cerebellar peduncle.

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And we have some nice little colors here

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for you to make it a bit easier.

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And those colors include the superior and medial

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and lateral vestibular nuclei.

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Over here, the medial longitudinal fasciculus,

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which can be affected in multiple sclerosis.

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We've got the medial lemniscus more towards the

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midline as a fairly large yellow structure.

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And then we've got this triad right here,

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which we're going to focus on.

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This is the trigeminal and mesencephalic nucleus of five.

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So, let's ignore that for right now.

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And then, we have seven and six.

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And we said seven and six are pretty intimate with each other.

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And let's look at what seven does.

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Seven has its nucleus and the fibers then course posterior

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around the abducens nerve,

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pass in front of this green structure,

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which is the trigeminal and mesencephalic nucleus of five,

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and then crosses directly in front of the trapezoid body,

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which is part of the hearing or auditory pathway,

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before it leaves the station in the region

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of the cerebellopontine angle.

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So, this looping effect of the 7th nerve around

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the abducens nerve nucleus is the main

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teaching point of this vignette,

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along with the fact that you have this very close

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triad of nuclei at the apparent origin of seven,

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which includes seven, five, and six.