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Dr. P here to talk about

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the real origin of the hypoglossal nerve,

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namely the hypoglossal nucleus.

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Now, I've got the hypoglossal nerve right there.

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I've got a couple bumps that we talked about previously.

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We've got a bump anteriorly, the pyramid,

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and you've got the olivary protuberance right here.

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So in a pre-olivary position sits the hypoglossal nerve.

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Now, what does the nerve do?

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Well, when it comes in,

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it actually has a posteromedial course where it sits

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directly underneath the fourth ventricle

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as the hypoglossal nucleus.

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Now, there are two paired nuclei,

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so there's obviously a hypoglossal nerve coming out the

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other side as well. I've drawn it a little bit crooked,

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but no matter.

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And the hypoglossal nucleus receives input from both motor

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cortices, but the contralateral input is dominant.

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So innervation of the tongue is essentially lateralized.

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Signals from muscle spindles on the tongue travel through

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the hypoglossal nerve, moving onto the lingual nerve,

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which synapses on the trigeminal

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and mesencephalic nucleus of nerve number five.

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There's also important contributions to the tongue musculature.

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So, in summary, the hypoglossal nerve,

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or the 12th cranial nerve,

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arises from paired nuclei in the most caudal aspect of the

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brainstem, posterior, underneath the fourth ventricle,

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the nerves course in the medullary space, in other words,

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in the medulla oblongata, anterolaterally,

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there's the apparent exit,

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then courses laterally where it reaches the hypoglossal

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canal now, and then descends behind the vagus

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nerve in the carotid space.

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Dr. P out.

The Real Origin of the Hypoglossal Nerve

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