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I want to talk to you about the 6th nerve,

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also known as the abducens nerve.

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I'm going to start out with a gross anatomic

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picture of the brainstem.

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And even though the abducens nerve comes

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out on the ventral side of the brainstem,

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I'm starting on the dorsal side for a good reason.

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We've got some gross anatomic structures here,

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like the middle cerebellar peduncle, a great landmark.

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This is a purely afferent structure connecting

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the brainstem with the cerebellum.

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But just medial to it is this bump

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with the dorsal median sulcus.

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And the bump, which is pretty elongated,

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is known as the facial colliculus bump.

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What sits under that colliculus?

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The facial nerve nucleus,

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the genu of the facial nerve,

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and the abducens nerve nucleus,

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which sits slightly dorsal to it.

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But they both lie directly underneath this facial

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colliculus bump at about this level,

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the inferior aspect of the pons near the ponto-midbrain

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junction at the level of the middle cerebellar peduncle.

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Now, let's flip it over.

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Let's go over to the ventral side, where we got this big,

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fat stuffy belly of the pons, rather plump.

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And on each side, we see the middle cerebellar peduncles,

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the pontomedullary sulcus,

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from which the 6th nerve will exit.

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This is known as the apparent exit of the 6th nerve,

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the apparent origin of the 6th nerve,

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because the true origin of the 6th nerve

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lies underneath that facial colliculus bump.

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Now, when the 6th nerve comes out,

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it's going to come out lateral to the pyramid.

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So here are the two pyramids.

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This is the medulla oblongata.

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Here's the anteromedian sulcus.

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So your 6th nerve is going to come out right about here,

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pontomedullary sulcus, lateral to the pyramid.

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Now, sometimes you'll see little linear structures

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coming out of here, but they light up with contrast.

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And these are small perforating vessels of the pontine circulation.

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Don't confuse those with the 6th nerve.

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So a very important landmark,

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lateral to the pyramid is

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identification of the apparent exit of the 6th nerve.