Hey guys, this is Peter from AnatomyZone and in this tutorial we're going to take a look at the blood supply to the spinal cord.
I'll first look at the arterial supply and then I'll move onto the venous drainage. With the arterial supply, essentially you have two sources which supply the spinal. You've got one source which arises at the level of the medulla oblongata inside the cranial cavity, and gives off branches which descend vertically down the length of the spinal cord. And you've also got vessels which feed in at each different segmental level, so these are the segmental spinal arteries, or the feeder vessels, as they feed in at each vertebral segment.
First we'll take a look at the vertical vessels which run the length of the spinal cord, so looking at this model here with the vertebral column, the spinal cord, and a few blood vessels, you can see the vertebral artery here coming off the subclavian on either side, and we'll just take a look at the right side, and you can see that the vertebral artery rises up and passes through the transverse processes of the cervical vertebrae.
This vertebra here is C6, and the vertebral artery passes first through the transverse process via the transverse foramen and ascends up towards the cranial cavity. After entering the cranial cavity through the foramen magnum, the vertebral arteries anastomose to form the basilar artery, but what we're interested in, is the vertebral arteries giving off the anterior spinal arteries.
You get this anastomosis coming off the vertebral arteries on either side, and this forms the anterior spinal artery, and this artery runs down the spinal cord its entire length and it runs anterior to the ventral median fissure, or the anterior median fissure. That’s one of the vertical vessels. The other two vertical vessels are the posterior spinal arteries, and you've got two posterior spinal arteries. Now if we just rotate the model around, so we can look at the posterior aspect of the spinal cord.
Posteriorly, you've got two branches given off from the vertebral arteries, which form the 2 posterior spinal arteries. These run the length of the spinal cord, down the posterolateral aspect of the spinal cord. You’ve got one anterior spinal artery, and 2 posterior spinal arteries, so these are the three vertical arteries which originate in the cranial cavity and descend the length of the spinal cord.
Now we'll take a look at the second arterial source to the spinal cord.
This is from the segmental vessels, and they're called this because they feed into the spinal cord at each different segmental level. They enter via the intervertebral foramina, along with the spinal nerve roots, and these segmental vessels are given off by different vessels depending on the region of the spinal cord that they supply.
In the cervical region, you've got the vertebral and deep cervical arteries which give off these segmental spinal arteries, and then in the thorax, you've got the posterior intercostal arteries, which give off these segmental arteries, and in the abdomen, the lumbar arteries give rise to the segmental arteries. For simplicity's sake I'm going to zoom into the thoracic spinal region and we'll take a look at the segmental blood supply there.
We're looking here at the thoracic region of the spinal column, and what you can see is that I've removed one of the thoracic vertebrae, and you've got the thoracic aorta anteriorly, you've got the spinal cord behind, and you've got the dorsal and ventral roots attaching to the spinal cord. And then coming off the thoracic aorta, you've got the posterior intercostal artery.
At the thoracic level, the segmental spinal artery is given off from the posterior intercostal artery, it then divides into two branches, you've got the posterior radicular artery, and the anterior radicular artery, and these follow along the dorsal and ventral nerve roots.
Also you'd have the anterior spinal artery running down in front of the ventral median fissure like this, and you'd be able to see one of the posterior spinal arteries, running down the posterolateral aspect. At every vertebral level, you've got this arrangement of a segmental spinal artery giving rise to a posterior and anterior radicular artery, but at some vertebral levels, you've got another branch, called the segmental medullary artery.
This comes off the segmental spinal artery, and it actually directly joins to the descending vertical arteries, so the anterior and posterior spinal arteries. This doesn't happen at every spinal level, but it's something to be aware of, and it acts to sort of reinforce the blood supply that's provided by these vertical descending arteries.
Also of note is that the largest segmental medullary artery is known as the arteria radicularis magna, which essentially is a descriptive Latin term for what I just said, so it just means the great radicular artery. And this arises in the lower thoracic and upper lumbar regions, and it helps to essentially reinforce the blood supply to the distal parts of the spinal cord.
That’s the arterial supply to the spinal cord.
Next we'll talk about venous drainage, and what I'd like to do is just switch over to a cross-sectional diagram to just explain the basic aspects of this system. We’re looking now at a cross-sectional diagram of the spinal cord and its roots.
Just before we talk about the venous system, I'll just draw on to this diagram what we've just talked about, so posterolaterally, you've got the posterior spinal arteries, and anteriorly in front of the ventral median fissure or anterior median fissure you've got the anterior spinal artery. And then you've got the segmental arteries given off by different arteries, so we talked about the thoracic level, so they were given off by the posterior intercostal arteries, so the segmental arteries on either side, and the segmental spinal arteries divide into posterior radicular arteries and anterior radicular arteries. And then we also discussed that at some vertebral levels you've got the segmental medullar arteries, directly given off from the segmental spinal arteries to join the vertical arteries.
Essentially you've got a similar structure to the venous drainage system of the spinal cord. You’ve got these longitudinal veins which run down the length of the spinal cord. You've got anterolateral and posterolateral veins, which sit either side of the dorsal and ventral nerve roots, so I'm just drawing these on.
As well as the anterolateral and posterolateral veins, you've got an anterior and a posterior spinal vein. All these veins that I've just mentioned basically drain via anterior and posterior radicular veins, and these veins then drain to a venous plexus, which sits in the extradural space, so you can see the dura mater covering the spinal cord here, so this venous plexus is known as the internal vertebral venous plexus, and it is situated in the extradural space, outside the dura mater.
Then what happens, the blood from the internal vertebral venous plexus then drains to another plexus, which is the external vertebral venous plexus. And the blood then essentially drains back into the big systemic veins, so the ascending lumbar vein, and the azygos veins, the hemi azygos and the azygos veins themselves.
That’s the blood supply to the spinal cord.