Hello all this is Dr. Alsup and I am very excited to get to talk about the meninges
as well as some of the specializations of the dura mater specifically these dural partitions
and we have quite a bit to go through so let's get started. Now recall the meninges
are membranous coverings of the brain and the spinal cord and there are three types of meninges.
The most external layer is the dura mater which is the toughest it is the thickest layer
it often looks pearly white or silver as you can see here and here. When the calvaria or that skull
cap is removed the first thing you should see is actually not the brain but the dura mater.
As you can see in this image here you can even see a bit of the dural venous sinus which is deep
or it's kind of between the two layers of the dura running right along here.
But the rest of what you see here is dura so it would have to be reflected the dura model would
have to be reflected in order to see the brain or any of the deeper layers of the meninges.
Moving to the deeper meninges you can see here these forceps are holding on to a portion of
the arachnoid mater. The arachnoid matter is thicker than the pia mater
and it can actually be dissected away from the brain. Sometimes it's very closely adhered to
the pia mater or to the dura mater dependent on the embalming process but you can actually
pull it away from the brain whereas with the pia mater it's so closely adhered to the brain
it cannot easily be dissected away and it's that pia mutter if you've reflected away the
arachnoid in the dura mater that gives the brain that kind of shiny appearance.
And so it gives the brain and the spinal cord that shiny appearance so speaking of the spinal
cord sometimes I think it's easier to see the deeper meninges in this region associated with the
spinal cord. So again the pia mater is very closely adhered to the spinal cord as well as to the brain.
And here in this image the forceps are actually holding the dura mater and the the arachnoid mater
is very closely adhered to the dura you can see it kind of running along right here you
can see portions of it here. But what's really nicely visible in this image are the arachnoid
trabeculae. And you can see these kind of extending throughout this region. It's these arachnoid
trabeculae that give the spider-like appearance associated with the arachnoid and thus its name.
The trabeculae are located within the subarachnoid space so any the space between
the arachnoid and the pia would be the subarachnoid space. Obviously it's been
quite a bit extended it's gotten larger because the forceps are holding it but the subarachnoid
space spaces between arachnoid and pia. You'd have the arachnoid trabeculae in addition to having
vasculature neurovasculature in that region and cerebrospinal fluid during life.
In certain areas there will be extensions of the arachnoid
mater as well as the subarachnoid space that will actually project into the dural venous
sinuses or some of the dural vena sinuses lateral extensions. And these are called
arytenoid granulations which allow CSF to drain and be reabsorbed into the venous sinuses.
And so you can see here I'm going to circle a few regions where you can really see
these arachnoid granulations a little bit deep and these regions right here on either side of the
the dural vena sinus right here which is the superior sagittal sinus are called lacunae.
So just kind of lateral extensions of the sinus and that's really where you'll see a
lot of these arachnoid granulations. You can have arachnoid granulations associated with numerous
different sinuses but by far their most frequent associated with the superior sagittal sinus.
Let's move to dural partitions or dural infoldings. But before we do it I want to take a second
and think what are these dural partitions composed of? And I'll give you a second, hopefully you're landing
on the fact that dural partitions are formed by the deeper layer of the cranial dura mater, the
meningeal dura, which is reflecting away from the periosteal dura in order to compartmentalize the
area and offer additional protection to certain neural structures so it's really that meningeal
dura that's reflecting away and creating these partitions. There are four dural partitions but
we're going to focus on the two that are the most easily observable. Here I'm going to outline the
first one we're going to discuss which is the falx cerebri we'll extend back into this region here.
And the falx cerebri is the largest of the dural partitions. It also has a very distinct
sickle shape. When the brain is present the falx cerebri is going to run down the middle
of the longitudinal cerebral fissure so between those two cerebral hemispheres
the falx cerebri will also house the superior sagittal sinus which you can see here
and the inferior sagittal sinus which is a little bit more difficult to view but would
be on this inferior border of the falx cerebri. You can also see a portion of the tentorium
cerebelli which is the second largest dural partition and it sits more transversely.
Whereas this was more longitudinal here with the falx cerebri the tentorium cerebellum will be more
transversely located. It will actually separate the cerebrum from the cerebellum. So in essence
separating the forebrain which sits above the tentorium and the hindbrain which sits inferiorly.
Now we are looking at a straight superior view here and the falx cerebri has actually been removed.
And this really allows for a really nice view of the tentorium cerebelli so you can really see how
it kind of just drapes over transversely this region. And you can see here as well this very
distinct curved notch right here and this is the tentorial notch. And it is here that the midbrain
sits during life so this cerebrum or the cerebral hemispheres will be above the
tentorium cerebelli. The cerebellum will be deep and the midbrain would sit right in this region.
Excellent, well thank you for joining me in this discussion of the meninges and some of
the dural partitions. As always take your time to review and reach out if you have any questions.