There are 24 articulating vertebra:
- 5 Lumbar
In between each vertebra you have an intervertebral disc, which forms a cartilaginous joint between the vertebra. These discs function to absorb shock and to allow slight movement between the vertebrae.
The intervertebral discs consist of an outer annulus fibrosis and an inner nucleus pulposus. A slipped disc occurs when this soft jelly like substance (the nucelus pulposus) protrudes through the annulus fibrosis and irritates the surrounding spinal nerve roots.
The vertebrae are numbered
So the cervical vertebra are referred to as C1-C7, the thoracic vertebra are referred to as T1-T12, and the lumbar vertebra are referred to as L1-L5. So C1 is the most superior cervical vertebra and C7 is the most inferior cervical vertebra, and the same for the thoracic and lumbar regions.
Why is this important?
Because in anatomy and in clinical medicine the vertebral levels are used as reference points to identify where other structures lie. For instance, when performing a lumbar puncture, so as to avoid damaging the spinal cord, the needle is inserted between the lumbar vertebra L3/L4 because in adults, it is known that the spinal cord ends at around the L1/L2 vertebral level.
- Cervical curve
- Thoracic curve
- Lumbar cure
- Pelvic curve
- Atlanto-occipital joint - flexion/extension, and slight lateral motion
- Atlanto-axial joint - twisting left to right
- Thoracic - rotation
- Lumbar - flexion and extension, lateral flexion, small amount of rotation
Okay so this is a tutorial on the spinal column, I'm also going to be doing one on the structure of the vertebra, and then the morphology of the different segments of the vertebral column, so how to identify the cervical vertebra, the thoracic vertebra and the lumbar vertebra. But this one will just focus on the spinal column, so it will be quite a short basic tutorial.
Here we've got...this is anterior here and this is posterior here.
The vertebral column consists of 24 articulating vertebra and then you've got the sacrum and the coccyx, which are fused vertebra.
Up here is the cervical vertebra, and you've got seven cervical vertebra, these are 12 thoracic vertebra, which articulate with the ribs, 5 lumbar vertebra, and then you've got the sacrum here - I'll just zoom in a little bit on that - which consists of 5 fused vertebra. And then you've got the coccyx, which consists of 3 to 5 five fused vertebra. Okay, so in between each vertebra, you've got an intervertebral disc, and this, the function of the intervertebral disc is really to absorb shock.
I'll just take a look at one of those a bit closer. I'll just get rid of that, click there.
Here you can just - zoom in a bit - this is an intervertebral disc, it's not the best illustration but basically you've got the outer annulus fibrosus, which is fibrocartilage, and then inside is the nucleus pulposus. The annulus fibrosus contains the nucleus pulposus, which is a sort of soft, jelly-like substance, and when you get a slipped disc, the nucleus pulposus herniates out through the annulus fibrosus and it can press on the spinal nerves, which gives rise to the symptoms. And when you get this in the lumbar region, you get sciatica.
You’ve got 7 cervical vertebrae, 12 thoracic vertebrae which articulate with the ribs, 5 lumbar vertebrae, a sacrum and coccyx, which consist of fused vertebrae.
It’s important to know about the vertebrae, because they're often referred to when you’re talking about anatomical landmarks, and also when you're talking about spinal nerves. The spinal nerves emerge from the intervertebral foramen, which I'll talk about in, when I talk about the structure of the vertebrae in the next tutorial, but the spinal nerves are numbered according to the level which they emerge.
The cervical vertebrae are C1 to 5, C1 to 7 sorry because there are 7 cervical vertebrae. Thoracic vertebrae are referred to T1 to T12. The lumbar vertebrae are referred to as L1 to L5. One of the funny things is that although there are only 7 cervical vertebrae, there are 8 spinal nerves, because the first cervical, sorry, spinal nerve C1 emerges between the first cervical vertebrae and the skull, whereas the others emerge from the intervertebral foramen, so you've got 8 cervical spinal nerves.
I'll just bring in the, some nervous tissue so I can show you where they emerge. Rotate around to the back, so you can see how they emerge from in between each vertebra.
If I just click on this one here, you can see that that is cervical spinal nerve C5. It’s important to know about spinal nerves when you're talking about myotomes and dermatomes. And just going back to what I was saying about anatomical landmarks, so for instance, the angle of Louis is known to be at the level of the junction of T4 T5, vertebral level T4/T5, and also the bifurcation, the bifurcation of the trachea, so you can see that is roughly at the level of T4/T5, and the...can't quite see it...but the arch of the aorta is also, the beginning and end of the arch of the aorta is roughly at the level of T4/T5.
That’s how vertebral levels are used to identify anatomical landmarks, so they're a good thing to know in that respect, sorry just got rid of everything there. Okay, so just a bit about the curves. You can obviously see that the spinal column is curved.
You’ve got this cervical curve, thoracic curve and the lumbar curve. And then you've got this pelvic curve, which starts at the junction of the sacrum and the lumbar, the lowest lumbar vertebra and ends at the coccyx - so that's the pelvic curve. And, so at birth you've got this one, you don't have all these curves you've just got one fixed curvature, which is the primary curvature and then you develop the cervical and the lumbar curves later in life, which are known as the secondary curvatures.
the movement you get at each level, at the atlanto-occipital joint, which is where this vertebra, vertebra C1 is known as the atlas, vertebra 2 is known as the axis, and a way of remembering the atlas, if you are familiar with Greek mythology, some Titan or something Atlas, known as Atlas, had to carry the universe or something, there's loads of pictures of this Greek Titan carrying the world, so I guess the skull is the world and that's why the Atlas is known as the Atlas. But anyway, this, I'll try and get the skull back so you can just see that. Okay got everything back, at this joint here, I'll show you. These two condyloid synovial joints are known as the atlanto-occipital joint, and at this joint you get a nodding motion of the head, so flexion and extension and you also get very slight lateral motion here, so this is the atlanto-occipital joint.
The next one down is the axis, so this one articulates with the atlas above, and here you get twisting left to right motion.
The thoracic vertebrae, you get rotation, and you don't really get flexion or extension here, because it's limited a lot by the rib cage, so you just get rotation. The lumbar vertebrae you get significant flexion and extension, you also get lateral flexion and you can also get a tiny amount of rotation.
That’s the spinal column, the next tutorials will be on the structure of the vertebra, so I'll be looking in detail at all these different processes and how to label and identify the different parts of the vertebra.