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. So I'll first look at the arterial supply and
then I'll move onto the venous drainage. So with the arterial supply, essentially you
have two sources which supply the spinal cord. 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. So 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. So 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. So 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.
So 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.
So 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. So posteriorly,
you've got two branches given off from the vertebral arteries, which form the 2 posterior
spinal arteries. So these run the length of the spinal cord, down the posterolateral aspect
of the spinal cord. So 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. So now we'll take a look at the second arterial source
to the spinal cord. So this is from the segmental vessels, and they're called this because they
feed into the spinal cord at each different segmental level. So 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. So 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. So 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. So 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. So 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. So 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. So 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. So this comes off the segmental spinal artery, and it actually directly joins
to the descending vertical arteries, so the anterior and posterior spinal arteries. So
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. So 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. So that's the arterial supply to the spinal cord. So
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. So we're
looking now at a cross-sectional diagram of the spinal cord and its roots. So 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. So essentially
you've got a similar structure to the venous drainage system of the spinal cord. So 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. So as well as the anterolateral and posterolateral
veins, you've got an anterior and a posterior spinal vein. So 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. So 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. So that's the blood supply
to the spinal cord.