OK so in this part of the tutorial, we're going to take a look at the coverings of the spinal cord - so the meninges, and we'll take a look at the basic elements of the internal structure of the spinal cord.
Down at the bottom is anterior and up at the top is posterior, and as I showed you before on the 3D models, we've got the ventral roots, which I've highlighted in purple. We've got the dorsal root ganglion and the dorsal root of the spinal nerve, so as I mentioned in the previous part the ventral root carries efferent motor information, and the dorsal root carries afferent sensory information.
Afferent arrives, efferent exits.
If you're familiar with the coverings of the brain, the spinal meninges are exactly the same, so you've got three layers, you've got the dura mater, the arachnoid mater, and the pia mater. Just like in the brain, the dura mater is this tough fibrous outer covering, which loosely envelops the spinal cord.
These meninges are actually continuous with the meninges of the brain.
You can see in this diagram the black line represents the dura mater, so this goes round the outside of the spinal cord and the structures that are associated with it. And then the light blue line represents the arachnoid mater, so between the dura mater and the arachnoid mater, you've got this space called the subdural space. And then likewise, between the arachnoid mater and the pia mater, you've got the subarachnoid space, and the subarachnoid space is important because this is where the cerebrospinal fluid, or CSF, circulates.
The pia mater is represented on this diagram by the red line which runs very closely to the dorsal roots and the spinal cord itself. The pia mater adheres very closely to the spinal cord structures.
One thing to mention about the pia mater is that midway between the ventral and dorsal roots, you've got this extension of the pia mater.
I'll just draw it on to this diagram here, so you've got the pia mater extending out at this point midway between the ventral and dorsal roots, and this extension is known as the denticulate ligament. Now I've switched over to this diagram here to illustrate the denticulate ligament more clearly.
We’re looking at a dissection of the spinal cord, and we've got the dura mater reflected back which I'm outlining in this light blue colour. We’ve got the spinal nerves that you can see in yellow and the denticulate ligament which I've highlighted in green.
You can see how it forms these triangular expansions.
The apices of these triangular expansions of the denticulate ligament attach to the dura mater. And you can see how the denticulate ligament emerges at intervals between the spinal nerves, to form these attachments to the dura mater.
Now we'll take a look at the basic internal structure of the spinal cord. You can see that in the middle there's this H-shaped configuration of grey matter, which I've outlined in light blue. And outside this, you've got the white matter, so peripheral to the grey matter you've got white matter.
The posterior projection of grey matter is known as the dorsal horn, and you can see that highlighted in yellow. And then ventrally, you've got the ventral horn, and in the upper lumbar regions and the thoracic regions of the spinal cord, you've got a lateral horn, so I've highlighted that in light blue. Now you'll also notice that there's these two grooves that run into the spinal cord, so anteriorly which I'm outlining in pink, you can see that there's a fissure which is known as the ventral median fissure. And posteriorly you've got the dorsal median sulcus.
The white matter which lies outside the grey matter can be broken into three regions in relation to these fissures and sulci and the horns of the grey matter.
Between the dorsal median sulcus and the dorsal horn you've got the dorsal funiculus, and between the dorsal horn and the ventral horn, you've got the lateral funiculus, and the ventrally you've got the ventral funiculus, between the ventral median fissure and the ventral root.
Right in the centre of the spinal cord, there's a little canal which I'm drawing on in green. This central canal is continuous at the top of the spinal cord with the ventricular system of the brain. You’ve got cerebrospinal fluid running through the central canal.
Essentially what you need to know is that the primary afferent sensory information that comes through the dorsal root and terminates in the dorsal horn, so the dorsal horn is the site of termination for most of these primary afferent sensory neurones, and it also forms the site of origin for the tracts which ascend to the brain.
The ventral horns are the site at which the motor neurones are given off. You’ve got the motor neurones, motor efferent neurones innervating the skeletal muscle originating in the ventral horn.
You get efferent motor information coming out via the ventral root. And then in the periphery of the cord, in the white matter, you've got the ascending and descending tracts.
We’ll talk about these in detail in other tutorials, but essentially, the main ascending tracts are the dorsal columns, the spinothalamic and the spinocerebellar tracts, and the main descending tracts are the corticospinal tracts, which are responsible for skilled voluntary movement.
one final thing to point out is that where the fibres cross over from one half of the spinal cord to the other, you've got something called a commissure, so within the grey matter, you've got the grey commissure centrally, so I'm just sort of drawing this on in yellow shading. And anterior to that, you've got a little bit of white matter, so this is called the ventral white commissure.