Anatomy of the Meningeal Region (Nursing)

00:01 Now, let's look at the coverings of the brain. If we start most superficially, we would have the skin.

00:09 And before we get to the underlying skull bones, we would hit a connective tissue wrapping that covers all bones called the periosteum, meaning, around the bone.

00:22 And the bones of the skull as we already mentioned, generally match up with the underlying lobes of the cerebrum.

00:28 For example, frontal and occipital. Deep to the bone, there is also periosteum but in the skull, we actually have something called the dura mater that serves a dual purpose of being periosteum as well as one of the first coverings of the underlying brain.

00:49 Deep to the dura mater is a much thinner layer called the arachnoid.

00:56 An arachnoid means spider-like and it has a very loose sort of web-like appearance compared to the dura mater which is very thick and hard.

01:07 Dura actually means hard, like something that's durable is very hard.

01:13 And then, deep to the arachnoid is something called the pia mater.

01:18 Now, this layer of brain coverings is directly attached to the surface of the brain and unlike the others, cannot be peeled apart from it. It's intrinsically attached to the underlying brain.

01:31 So, collectively, those three things, the dura, arachnoid, and pia make up the meninges.

01:39 And again, the dura is sitting just underneath that skull bone.

01:44 So, the outer portion of the dura is actually called the periosteal layer because it's essentially serving as the periosteum on this side of the skull bone.

01:54 The inner portion is called the meningeal layer of the dura mater and for large portions of the meninges, the two are directly attached to each other and look like a single sheet.

02:06 But at various portions throughout the brain, they'll separate to create a space where venous blood can flow and we call these dural venous sinuses and they're very important for venous drainage of the brain.

02:23 Deep to the dura mater, we again have the arachnoid which is much thinner.

02:28 It's not as tough and strong as the dura mater. And then, again, the pia mater is the layer that's directly on the surface of the brain itself and can't really be separated from the underlying brain.

02:42 We do have a bit of a gap between the arachnoid layer and the pia mater though and we call that the subarachnoid space and it's a small space but within that space, we have a fluid called cerebrospinal fluid that cushions the brain.

03:01 And at certain portions, in contact with the dural venous sinus, there's projections of this subarachnoid space that go into the dural venous sinus called arachnoid granulations and this provides a pathway for cerebrospinal fluid to exit the subarachnoid space and enter into the dural venous sinus.

03:26 So, cerebrospinal fluid or CSF is produced deep in the brain by structures called the choroid plexus.

03:38 And then, it fills and flows through spaces inside the brain called ventricles and these ventricles have communications that allows the CSF to pass into the subarachnoid space that covers the brain.

03:56 And there are other passageways for this CSF fluid to exit the subarachnoid space but one of them is the arachnoid granulation. Again, this is a way for that cerebrospinal fluid to exit into venous circulation and essentially exit out of this relatively confined space.

04:19 And that way, the pressure of this fluid doesn't get too great and compress the brain.

04:27 This way, excess CSF can get into a dural sinus which is again, full of venous blood that's going to exit the skull altogether and head down towards the heart.

04:41 Here is an example of what the ventricles would look like.

04:45 Again, there's spaces deep inside the brain that form from the very earliest stages of brain development when the brain started out as a tube.

04:55 This was essentially what's left over of that tube portion, that hollowed portion that now houses the choroid plexus and the cerebrospinal fluid.

05:06 The dural venous sinuses are scattered throughout various portions of the meninges but there are some major ones found particularly near the midline called the superior sagittal sinus which is a very descriptive term.

05:24 This one sits superiorly and it's in the midsagittal plane.

05:30 And then, there's another one that parallels it but is a bit further down and a bit shorter called the straight sinus and this one is also draining some deeper venous structures that are very far down into the brain.

05:44 But where these two midline-type structures meet is something called a confluence of sinuses that drain into the transverse sinus.

05:56 Now, the transverse sinuses on either side as you might guess run transversely and they're eventually going to drain out of the skull altogether into the internal jugular vein on its way down to the right side of the heart.