Which cranial nerves are ipsilateral

[Medicman13]

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Do cranial nerves 5,6,8,10,12 end up being ipsilateral cranial nerves that do not decussate to innervate their end target organs,muscles,etc?
Thanks for the help

 

[Aclamity]

Do cranial nerves 5,6,8,10,12 end up being ipsilateral cranial nerves that do not decussate to innervate their end target organs,muscles,etc?
Thanks for the help

Not sure if I understood your question correctly, but all the CNs are peripheral nerves, so they are all ipsilateral

 

[hotchik]

Not sure if I understood your question correctly, but all the CNs are peripheral nerves, so they are all ipsilateral

I thought all CN's decussate after leaving the brainstem...where only CN4 decussates immediately

 

[GTP]

I thought all CN's decussate after leaving the brainstem...where only CN4 decussates immediately

All of them are ipsilateral except cn 4. But if it's a unilateral corticobulbar tract lesion (Cns), then the contra lateral 12 and 7 cn nerves are affected. Everything else gets dual innervation by the corticobulbar tract.

 

[ijn]

I thought all CN's decussate after leaving the brainstem...where only CN4 decussates immediately

Not quite. The lower motor neuron exiting the brainstem for everything but CN IV is ipsilateral to its cranial nerve nucleus. The upper motor neuron for every single cranial nerve descussates in the brainstem just like any other upper motor neuron. CN IV is just more confusing in that the lower motor neurons cross over as they leave the brainstem. So the left CN IV nucleus controls the right superior oblique, and is also innervated by the right pre-central cerebral cortex. None of the others do that. In general a cranial nerve innervates muscles that are ipsilateral to its nucleus, and contralateral to the brain hemisphere that controls it. Of course, this is ignoring that a lot of the muscles in the head receive innervation from both sides of the brain.

 

[phoenix89]

Not quite. The lower motor neuron exiting the brainstem for everything but CN IV is ipsilateral to its cranial nerve nucleus. The upper motor neuron for every single cranial nerve descussates in the brainstem just like any other upper motor neuron. CN IV is just more confusing in that the lower motor neurons cross over as they leave the brainstem. So the left CN IV nucleus controls the right superior oblique, and is also innervated by the right pre-central cerebral cortex. None of the others do that. In general a cranial nerve innervates muscles that are ipsilateral to its nucleus, and contralateral to the brain hemisphere that controls it. Of course, this is ignoring that a lot of the muscles in the head receive innervation from both sides of the brain.

Hmm that makes sense. And all nerves receive dual supply except for Nerve VII and XII? I had heard about VII but didnt know XII receives supply from only one hemisphere as well, can anyone confirm this

 

[lemonade90]

ijn is right. However I am not sure all the cranial nerve recieve bilateral innervation.

CN VII is a case that is definitely the example most often given. It has two nuclei (one controlling the upper part of the face, the other controlling the the lower part of the face). The upper nuclei is innervated bilaterally while the lower recieves input from only the contralateral side. If you damage one motor homunuclus cortex, all of your upper face muscles should be working (because the upper nuclei is bilaterally innervated) while only the contralateral lower face should be droopy.

 

[The kitchen sink]

I'm scared. all this sounds like a lost ancient language to me.

 

[GTP]

Hmm that makes sense. And all nerves receive dual supply except for Nerve VII and XII? I had heard about VII but didnt know XII receives supply from only one hemisphere as well, can anyone confirm this

Cn xii technically receives bilateral innervation. But the contra lateral one is predominant. So a left corticobulbar tract lesion will affect the right nucleus, right nerve, your tongue sticks to the right.

 

[Suncrusher]

I'm scared. all this sounds like a lost ancient language to me.

+1. I instantly forgot all neuro the minute my neuro block ended. That was only 3 months ago but I had so much trouble remembering it on the end-of-year cumulative NMBE I just took. Sigh.

 

[Azipropofol]

lol me too Suncrusher. I usually go with the "that sounds about right" answer... the good news is we know more than we think we do.

 

[Morsetlis]

Not quite. The lower motor neuron exiting the brainstem for everything but CN IV is ipsilateral to its cranial nerve nucleus. The upper motor neuron for every single cranial nerve descussates in the brainstem just like any other upper motor neuron. CN IV is just more confusing in that the lower motor neurons cross over as they leave the brainstem. So the left CN IV nucleus controls the right superior oblique, and is also innervated by the right pre-central cerebral cortex. None of the others do that. In general a cranial nerve innervates muscles that are ipsilateral to its nucleus, and contralateral to the brain hemisphere that controls it. Of course, this is ignoring that a lot of the muscles in the head receive innervation from both sides of the brain.

Exactly. 🙂

It helps to remember brainstem pictures. None of those CN's cross the middle before the innervated target, except CN2 and CN4, which decussate toward the back in the region of the midbrain tectum. The difference is that all corticobulbar fibers decussate, but the optic radiations do not. Therefore, the left forebrain is associated with the right visual field of each retina, the left superior oblique muscle, and the right side of the body for all other corticobulbar functions.

Other interesting things to remember would be bilateral UMN innervation of the motor nucleus of CN7, so that you can differentiate between a Bell's Palsy (LMN lesion of CN7) and a hemifacial palsy (UMN lesion of CN7). Other people mentioned other stuff up there, too.