hello all this is dr. Alsup and in this video we will be discussing the meninges and in particular
the cranial meninges as there are some distinct differences particularly in the dura to the
spinal meninges so let's get started so the major learning objectives covered in this video include
a review of the three types of meninges with a focus on the difference between the cranial and
the spinal specifically dura mater and we will spend the last portion of this video discussing
the dura partitions or in foldings so what they are and where they're located all right recall
that the meninges are membranous coverings of the central nervous system so this will include both
the brain as well as the spinal cord so a lot of the images or the illustrations we have are going
to be at the spinal cord because sometimes it's easier to conceptualize there even though the
focus of this particular video will be on the meninges of the brain the major function of the
meninges is to protect and support both the brain and the spinal cord but also it's important to
note that the meninges will form a supporting framework for dural venous sinuses veins and
arteries in addition to enclosing that fluid filled subarachnoid space which is really vital
to normal CNS function there are three meninges there will be the tough or thick external fibrous
layer or the dura mater the thin intermediate layer which is going to be the arachnoid mater and
then the thin but delicate internal vascularized layer which is the Pia mater so kind of going from
superficial to deep the right node in the pm8 are actually continuous and when discussing together
you often hear the term leptomenex when you're talking about the arachnoid and the pia the dura
mater is the first thing one sees when performing a craniotomy if you remove the calvaria before you
even see the brain you'd be looking at the dura mater but it really is going to be all over the
place when we're discussing the internal portions of the cranium as mentioned the dura mater in the
skull as unique as there are two layers associated with the cranial meninges instead of just the one
dura mater layer associated with the spinal cord there is the periosteum sometimes you'll hear it
referred to as the industrial layer you'll hear either way this is the outermost or moer most
superficial layer and this is what's going to line the cranial cavity and you can see a
bit of this has been kind of pulled away from the bone here and so this will be the periosteal dura
the meningioma is the inner dural layer and it's typically closely applied to both the periosteal
dura mater and the arachnoid mater in fact the periosteal and meningeal layers are most often
closely adhered to one another except for in a few specific but important areas and you can see
the meningeal dura kind of reflecting away from the periosteal dura right here and so you can see
that's creating this space right here which will actually be a dural venous sinuses it can continue
to create these areas called dural partitions and that will be these specializations of meningeal dura
as mentioned above the arachnoid and the PIA mater are often discussed together the arachnoid
mater loosely translates to spidery mother this is named so because of these arachnoid excuse-me
trabeculae that will kind of extend through the subarachnoid space these trabeculae are composed
a flattened irregularly shaped fibroblast that are going to bridge the subarachnoid space now
the arachnoid is thin but it can be manipulated with forceps so the forceps in this particular
image are pulling the dura but you can move the arachnoid mater it's certainly more so than the
Pia mater all right noid although closely applied to the meningioma of dura mater is not a directly
attached to the dura instead it's held against the inner surface of the dura by the pressure of the
cerebrospinal fluid or the CSF in the subarachnoid space the Pia mater is even thinner than the
arachnoid mater and it's very difficult to kind of see or define as a layer on a gross level but it's
what gives the brain in the spinal cord that shiny appearance so it's kind of right on top of the
brain in the spinal cord it is highly vascularized by a network of fine blood vessels and where will
adhere to the surface of the brain and follow all of its contours for example when the cerebral
arteries penetrate the cerebral cortex the pia will actually follow along the artery for a short
distance so it's really closely adhered to those dips into the fissures and the sulci now that
space between the arachnoid and the PIA mater that have these are these right nora Bekele spanning
throughout is called the subarachnoid space so the subarachnoid space will house the cerebral spinal
fluid which we will talk about more detail in the ventricles video but it'll also have vasculature
that's going to travel within the space so a very important area note and this is an important note
the subarachnoid space is a real space so it has things in it during life it's an actual
space during life it is not a potential space and we will be discussing some potential spaces and
subsequent videos like the subdural or epidural spaces that that they these do not typically
exist in normal healthy adults but can form as a space of infection or blood enters the area due
to infection or injury so the subarachnoid space is a true space it is not a potential space in
certain areas portions of the arachnoid will kind of fold up and project into dural venous sinuses
which form between the periosteal meningeal dura in certain areas because they project into these
sinuses and their associated lateral projections called lacunae they are able to drain CSF into the
venous sinuses when drainage needs to occur this is particularly evident with the superior sagittal
sinus but can occur in other dural venous sinuses these granulations will cause the bone around it
to erode or pit and you can see some of these in this particular donor right here and these
areas on the bone or bone are called granular foveal a returning to the cranial dura mater in
certain areas that meningeal layer will reflect away from the periosteal dura creating these
specializations of the meningeal dura referred to as dural in foldings i often like to refer
to them as dural partitions these dural partitions often house dural venous sinuses which we'll talk
about a great deal a great bit more detail in the dearl being a sinus lecture these partitions or
dural septa between certain parts of the brain will really help to support certain areas all
right so there are four dura partitions the fox cerebri which you can see here is the largest
it will be located in that longitudinal cerebral fissure between the cerebral hemispheres during
life the brain has obviously been removed in this dissection this fox cerebri has a very
distinct sickle shape and extends from the crista galli anteriorly all the way towards the internal
occipital protuberance on the posterior portion in both the superior sagittal sinus and the inferior
sagittal sinus will be associated with the Falx cerebri the tentorium cerebelli is the second
largest partition and will separate the cerebrum specifically that occipital lobe of the cerebrum
and the cerebellum and you can see that over here this is part the tentorium cerebelli and you can
really see its expanse on this particular image this whole area right here and right here will be
part of the tentorium cerebelli this partition will attach to the client ID processes of the
sphenoid it will extend back towards the petrous part of the temporal bone which would be here
in here and it will also extend to the parts of the internal surface of the occipital bone so a
fairly large expanse it will also create this region right here called the tutorial knotch
and the midbrain will sit right here during life and it will also serve to separate the
tentorium cerebelli from the diaphragmatic cell a which is going to be right around this region
okay the last two Dural partitions and in this particular image the tentorium cerebelli has
been removed to get a slight glimpse of the fox cerebelli which is right in this region right
here this partition is quite small and during life is located between the cerebellar hemispheres this
also has an attachment on the internals occipital protuberance similar to that falx cerebri but it
will extend inferiorly and the occipital sinus will be associated with the Fox cerebelli the
fourth and last dural partition is the diaphragm sellae and this is going to form a roof over the
hypophyseal fossa so you can see a bit of it right here and right here ish but it's gonna have an
aperture for passage of the infundibulum and you can actually see a bit of the infundibulum right
here which is often referred to as a pituitary stalk as well as allow for hypophyseal veins to
kind of move in this region so a fairly small circular horizontal sheet over this area but
you can see it's a little bit more difficult to see than some of the other dural partitions so
that is the cranial meninges inderal part let's take a minute to review all right what do you
think about this question which portion of the meninges will form the dural partitions is it
the arachnoid mater is it the meningeal dura mater is it si periosteal dura mater or D Pia
mater take a moment pause the video if you need to try to answer this without going back through your
notes and once you are ready let's discuss how B or that meningeal dura mater is the correct answer
it is the meningioma da that reflects away from its close adherence to the periosteal dura mater
to form the dural and foldings or partitions the periosteal dura mater is the part that's at at or
is very closely adhered to the bone and so it is the deeper meningioma mater that will reflect away
the arachnoid and the PIA mater are not involved in the dural partitions as its name would suggest
so those two are not the correct answer alright so that wraps us up in regards to the meninges
and the dura partitions we will return to some of these concepts when discussing the dural venous
sinuses as well as the discussion of the cerebral spinal fluid in the ventricles video thank you so
much for your attention as always please do feel free to reach out with any questions