Another anatomy 101 question - spine

[Phloston]

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Another basic MS1 anatomy concept that I'm struggling with:

Spinal nerves C1-C7 exit above their corresponding vertebrae, so a C5-C6 disc herniation would impinge on the C6 nerve route.

All of the other spinal nerves exit below their corresponding vertebrae. What I don't understand is why an L5-S1 disc herniation therefore impinges on S1, not L5. Wouldn't L5, not S1, lie at the L5-S1 disc level?

 

[cbrons]

Another basic MS1 anatomy concept that I'm struggling with:

Spinal nerves C1-C7 exit above their corresponding vertebrae, so a C5-C6 disc herniation would impinge on the C6 nerve route.

All of the other spinal nerves exit below their corresponding vertebrae. What I don't understand is why an L5-S1 disc herniation therefore impinges on S1, not L5. Wouldn't L5, not S1, lie at the L5-S1 disc level?

There are 33 vertebrae, 31 pairs of spinal nerves.

C1 exits above the atlas, C2 above the axis (C2), C3 spinal nerve above C3, etc. and this trend continues until you reach the C8 spinal nerve, which exits BELOW the C7 vertebrae, above T1. Then the T1 spinal nerve (and all nerves after) exists below the vertebrae so named.

As far as posterolateral disc herniations, I attached a picture can help you better understand.

as you can also see, sometimes (but not usually) disc herniations can affect lower spinal nerve roots.

 

[loveoforganic2]

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[Phloston]

So the idea is that you've got the L5 vertebra, then the L5 nerve coming out below it, THEN the L5-S1 disc, then the S1 vertebra, then the S1 nerve.

So if the L5-S1 disc herniates posteroinferolaterally (which apparently is most common, right?), then it wouldn't encounter the L5, but instead the S1 nerve, because the L5 nerve is superior to it.

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I really like that picture you've posted. Do you have one for the cervical nerves? I can't seem to find a good one online.

 

[cbrons]

So the idea is that you've got the L5 vertebra, then the L5 nerve coming out below it, THEN the L5-S1 disc, then the S1 vertebra, then the S1 nerve.

So if the L5-S1 disc herniates posteroinferolaterally (which apparently is most common, right?), then it wouldn't encounter the L5, but instead the S1 nerve, because the L5 nerve is superior to it.

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I really like that picture you've posted. Do you have one for the cervical nerves? I can't seem to find a good one online.

The L5 nerve exits below the pedicle of L5, at the top of the intervertebral foramen.

As far as I understand, posterolateral herniations are the most common (and by far more common in the lumbar region). There can be a more medial protrusion of the disc, which has a greater propensity to damage (in addition to the spinal nerve) the roots traveling below (so btw. L4 and L5, it may impinge the L5 nerve but also S1, S2, etc.)

Just as a note, there is no IV disc below the L5-S1 level, and there is no IV disc between C1 and C2.


I attached 1 picture that I edited to illustrate this concept from Netter. I hope it helps, and this is how I understand it. Hopefully no one will tell me I am in error here...

 

[LoveMyRam]

Exactly, and its due to the fact that as we develop and grow as children, the vertebrae extend, bringing their nerves with them slowly, so as you go down the spine, you see lower vertebrae that have their respective spinal nerves that originate near levels higher up in the spine. I attached a good picture that reiterates the point you made and uses the same picture above. I'm trying to attach one for the cervical nerves but the file is too large.

So the idea is that you've got the L5 vertebra, then the L5 nerve coming out below it, THEN the L5-S1 disc, then the S1 vertebra, then the S1 nerve.

So if the L5-S1 disc herniates posteroinferolaterally (which apparently is most common, right?), then it wouldn't encounter the L5, but instead the S1 nerve, because the L5 nerve is superior to it.

-------

I really like that picture you've posted. Do you have one for the cervical nerves? I can't seem to find a good one online.

 

[LoveMyRam]

 

[golgiapparatus88]

A posterolateral herniation between, say C4 and C5 may impinge what nerve?

Answer: the C4 spinal nerve, because it exits above the pedicle of C4.

Forgive me for not following along with this point. If the cervical nerves leave above their corresponding vertebrae, why is it not the C5 nerve? (which would be the nerve found between C4-C5). I would have thought that for impingement of C4 to occur you would need herniation of between C3-C4.

Hope you can clear this up for me.

 

[cbrons]

Forgive me for not following along with this point. If the cervical nerves leave above their corresponding vertebrae, why is it not the C5 nerve? (which would be the nerve found between C4-C5). I would have thought that for impingement of C4 to occur you would need herniation of between C3-C4.

Hope you can clear this up for me.

You're right, I was actually incorrect. The spinal cord should end ~L2 in adults, so that spinal nerves after that should be coming off the cauda equina, and I believe this is why the lower spinal nerves cross the IV discs. So I edited my above post.

 

[golgiapparatus88]

teamwork for the win 👍

 

[cbrons]

teamwork for the win 👍

👍

 

[Phloston]

Thanks for all of the input.

 

[HSE21]

I think the simplest way to think about it is that you have 8 cervical spinal nerves but only 7 cervical vertebra. Which means one has to come from above c1 and one from below c8.
But in the case of the lumbar spinal nerves, you have 5 Lumbar vertebra and only 5 lumbar spinal nerves i.e L1 below first lumbar. L2 below second lumbar ...etc.
so when it is between C4-C5 (it would be the C5 spinal nerve)
or between L4-L5 (L4 spinal nerve)
note : the 5th lumbar spinal nerves are the thickest and their foramina the narrowest.which increases their chances of compression.

Q: Which part of the nerve is compressed, the anterior root or posterior or the anterior rami or posterior in posterolateral herniation ? (this Q came up in an MCQ a year ago)

 

[Phloston]

Q: Which part of the nerve is compressed, the anterior root or posterior or the anterior rami or posterior in posterolateral herniation ? (this Q came up in an MCQ a year ago)

Is it the posterior root? I'm not entirely sure. Could you please explain?

 

[thehundredthone]

A posterolateral herniation would first affect the anterior aspect of the cord. Remember that the disc lies anterior to the cord.

 

[Phloston]

A posterolateral herniation would first affect the anterior aspect of the cord. Remember that the disc lies anterior to the cord.

Yeah but isn't it the posterior roots of the respective spinal nerves that are compressed?

 

[phd89]

great points guys

 

[sigcodeprn]

Is it rare to have a disc herniation at C-7-T-1 ? and if so what would cause a herniation at that location. possibly a whiplash injury?

 

[sigcodeprn]

Will a concussion always show up on a Diffuse tensor image? Would it show up 11 months after the initial injury? Just a mild concussion from a whiplash injury with no impact.

 

[mmmcdowe]

Is it rare to have a disc herniation at C-7-T-1 ? and if so what would cause a herniation at that location. possibly a whiplash injury?

Will a concussion always show up on a Diffuse tensor image? Would it show up 11 months after the initial injury? Just a mild concussion from a whiplash injury with no impact.

It seems that you are seeking medical information for real life, and as such I strongly recommend consulting your physician rather than an anonymous forum.