Hi guys this is Peter from AnatomyZone and in this tutorial we're going to take a look at the anatomy of the spinal cord, so to begin with we'll look at the external features and then we'll move on to some of the basic internal anatomy of the spinal cord.
What we're looking at here is a model of the vertebral column containing the spinal cord, and you can see the brainstem at the top.
Rostrally, or at the top, the spinal cord is continuous with the medulla oblongata of the brainstem, and in adults, the spinal cord extends to the intervertebral disc between vertebral bodies L1 and L2.
I've just zoomed into the lumbar region of the vertebral column, and if I rotate the model round slightly, you can see the distal end of the spinal cord terminating at this level between vertebra L1 and L2.
The spinal cord is essentially a segmental structure, so it consists of 31 segments, you've got 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal segment. And these segments give rise to spinal nerves, so you can see the spinal nerves coming off either side of the spinal cord, and the spinal nerves are paired, so you've got spinal nerves emerging on either side of the spinal cord.
You’ve got 31 segments of the spinal cord giving rise to 31 pairs of spinal nerves.
Just taking a look at the shape of the spinal cord itself, you'll notice that essentially it's a cylindrical structure, but there are two areas of the spinal cord which are slightly enlarged, so you've got a cervical enlargement and a lumbar enlargement.
I've just switched over to a diagram to illustrate this, and on the left we're looking at the anterior aspect of the spinal cord and on the right we've got the posterior aspect.
You can see that there's this bulging out of the spinal cord in the cervical region, and the same in the lumbar region, so the cervical enlargement corresponds to the segment C4-T1, the lumbar enlargement corresponds to segments L1 to S3. And it's in these areas where the nerve plexuses, which innervate the upper and lower limbs respectively, emerge.
This is why that area of the spinal cord is thickened, because a lot of nerves supplying movement in the upper and lower limbs emerge from these areas.
Just coming back to the 3D model, we're taking a look at the distal end of the spinal cord, and you can see that it terminates in this conical structure, which I've highlighted in green. And this is known as the conus medullaris. And extending from the tip of the conus medullaris you've got a strand of connective tissue, which attaches the conus medullaris to the first coccygeal vertebra, and this strand is called the filum terminale.
I've just drawn that on there in yellow. As you can see the lumbar and sacral spinal nerves kind of hang down from the conus medullaris and they form this kind of arrangement which looks like a horse's tale, so the Latin for this is cauda equina, and this is what that collection of spinal nerves is known as.
Just coming back to this model here with the vertebral column shown, you can see how the pairs of spinal nerves emerge from between the vertebra.
I'm just drawing this on in green, so you can see the 31 pairs of spinal nerves emerging from the intervertebral foramina between the vertebra. Let’s just take a look at how the spinal nerves attach to the spinal cord.
What we're looking at now is the cervical region of the spinal cord, and you can see that I've removed one of the cervical vertebra just so we can take a look at how the spinal nerves attach to the spinal cord. You can see that there are these little rootlets which are attached to the spinal cord, and these rootlets then converge to form the ventral and dorsal roots.
If I just rotate the model around, you can see that there is a root at the front and a root at the back, so that's the dorsal root, and these roots converge to form the spinal nerve itself, and the spinal nerve exits the vertebral column via the intervertebral foramina.
Immediately after leaving the intervertebral foramina, you can see that there's another division, so the spinal nerve divides into a ventral and dorsal ramus. It's not actually shown clearly on this model here, but the ventral ramus is a lot thicker than the dorsal ramus, so it essentially what you need to know is that the ventral ramus supplies the muscles and skin of the front of the body and the dorsal ramus supplies the muscles and skin of the back.
If I just rotate the model round slightly more, you'll notice that there's this kind of swelling of the dorsal root, so this is known as the dorsal root ganglion, and this dorsal root ganglion contains the cell bodies of the primary afferent neurones, which enter into the dorsal horn of the spinal cord.
The cell bodies of the ventral root are actually contained within the gray matter of the spinal cord.
I'll talk about this in more detail in the next part of the tutorial but essentially you've got primary afferent neurones entering via the dorsal root, and you've got the efferent neurones leaving via the ventral root. How can you remember which is afferent, which is efferent, and which contains sensory and which contains motor. Well you can use the mnemonic: afferent arrives, and efferent exits.
With any structures in the nervous system, afferent will mean information is brought to that structure, and efferent means information is taken away from that structure.
Afferent arrives, efferent exits.
With regards to the dorsal roots, you can use the mnemonic, SAME DAVE, so sensory afferent, motor afferent - SAME. And DAVE, dorsal afferent ventral efferent. Using that mnemonic you can work out that the dorsal root carries sensory afferent information, and the ventral root carries motor efferent information.
in the next part of the tutorial we're going to take a look at a section, a transverse section, so if I just rotate the model round the side like that we're going to take a section through the spinal cord like this, and we'll look at the internal structure of the spinal cord and the layers that cover it, so the meninges.