Meninges and Dural venous sinuses

okay we're going to talk about meninges and dural venous sinuses and answer the questions what are the meninges what are dural venous sinuses and what is the deal with the cerebral circulation hello everyone my name is dr morton and i'm the noted anatomist so here we're going to take this coronal section at the top of the skull and blow it up and we can see the layers of the scalp and deep to that the skull bones deep to that the meninges and deep to that is the brain tissue and our focus is going to be

right there on the meninges specifically the dura mater and the arachnoid monitor and the pia mater okay and so here are all the things with the dura arachnoid and pm models that we're going to talk about we're going to start with the dura mater and that it consists of really two different layers so the dura mater is the most superficial layer of the meninges right there and it is the the latin for dura is tough or latin of tough is dura and the latin of mater is mother it literally means the tough mother because the

dense the dura mater is consisting of dense irregular collagenous connective tissue it's very tough and there are two layers to the dura mater a periosteal layer that lines the internal surface of the skull and the meningeal layer that's continuous with the brain and spinal cord so there's our dura mater and there's layer one all on the internal surface of the skull it's basically the periosteum on the inside of the skull and it ends at the foramen magnum now the second layer of the dura mater here in orange that's one that's going to be continuous with

the brain and all the way down the spinal cord and now we're going to go to the dural septae and the dural septae they're two so basically the two dural layers are bound together and only separate when they form dural septa or dural venous sinuses so in this coronal section we zoom in there's the skull and inside lining that and then there's the brain and there's our dura mater now watch the dura mater is together there's actually two layers the whole way and now they divide into a periosteal and a meningeal layer and when they

divide that's when you see the dural septa and that's when you see a dural venous sinus so the dural septae restrict displacement of the brain much like a seat belt does for us when we're driving around the car it keeps us the valuable things inside the car stable same with the dura mater with the valuable thing in the brain and the skull the brain the folk cerebri the tentorium cerebelli and the falx cerebelli are the three things we're going to talk about let's start with the falx cerebri where falx is latin for sickle so here

is this posterior superior view of the skull the dural septae are shown and the brain's removed and there's our folks cerebri and it does kind of look like a sickle like that and it courses anteriorly from the crysta galli of the ethmoid bone all the way back and it fuses with the tentorium cerebelli and on the very top of the mohawk is the superior sagittal sinus and the bottom is the inferior sagittal sinus the falx cerebri is vertical and it separates our cerebral hemispheres within the longitudinal cerebral fissure so there's the falx cerebri there are

the two cerebral hemispheres that it is dividing within that longitudinal cerebral fissure and the very bottom is the corpus callosum now the tentorium cerebelli is a bit different in that it is horizontal and oh hi ireland uh it's my daughter ireland okay so the tantorum cerebelli it's horizontal and it separates our occipital lobes and cerebellum and so here we're now going to see the same view and there's our tentorium cerebelli and it is going to be horizontal perpendicular to the falx cerebri so here's a posterior view of the brain and there's our two cerebral hemispheres

and there's our two cerebellar hemispheres and there's the spinal cord so now we're going to take this picture and go shing and put the skull around it and then notice there in yellow is the periosteal layer of the dura mater and in orange there is the meningeal layer and notice that the periosteal layer fuses at the frame and magnum and the meningeal layer goes all the way down the spinal cord so there is our tentorium cerebelli it's separating our cerebellum from occipital lobe and there's our folks cerebri that is vertical tintorium cerebelli horizontal so now

what we're going to do is we're going to take this section and move it back a little bit and this is the view that we're going to see okay we're behind now we're more posterior to the frame and magnum and we're going to see the falx cerebelli which is located between cerebellar lobes so there's the falx cerebelli which is right along the vermis between the two cerebellar hemispheres and then the tentorium cerebelli which is separating the cerebellum from the occipital lobe and there's the falx cerebri now we're going to talk about dural venous sinuses and

drovina sinuses are venous channels located between periosteal and meningia layers of dura mater and they receive blood from the cerebral veins primarily but also diploic diploic and emissary veins so let's talk about the venous channel so there is the dura mater and layer one and layer two and between the two layers is the dural venous sinuses and in this case we're sewing the superior sagittal sinus and the dry venous sinuses receive blood primarily from cerebral veins and so there is a cerebral vein and you see it dumping into the dural venous sinus but you also

have some of these and that is the big one that's what put a star there that's the main thing all these cerebral veins like the great vein of galen all these are going to eventually end up in a dural venous sinus okay the emissary veins go from the scalp through the skull and they drain into one of the dural venous sinuses and the diploic veins go from basically the skull into one of these drovino sinuses now dural venous sinuses are similar to veins in that they contain venous blood deoxygenated blood and they're lined with endothelium

but dural venous sinuses are not similar to veins in that they lack valves which means blood can flow in any direction and they lack a tunica media because it's basically dura mater dense connective tissue lined with endothelium that's what a dural venous sinus is and here are the dural venous sinuses okay this posterior superior view and there's our superior sagittal sinus along the top of the falx cerebri the inferior sagittal sinus along the bottom of the falx cerebri and there's our straight sinus right in the middle of our tentorium cerebelli and then our transverse sinus

that's causing horizontally along the back or posterior surface of the falx uh um cerebelli up the tentorium cerebelli and there's our sigmoid sinus it gets its name because it's s-shaped or sigmoid-shaped and then there's our superior and inferior petrosal sinuses that are draining down to the transverse sinus or sigmoid sinus and then there's our cavernous sinus and that's going to be a big one i'll talk about a second now all these drovenal sinuses ultimately drain into the internal jugular vein now let's go back for a second and talk about this cavernous sinus the cavernous sinus

is located on on this each side of the cela turcica the pituitary gland and cranial nerves three v 1 and 2 course through the lateral wall and cranial nerve 6 and the internal carotid artery course through the middle let's do that again so here's the pituitary gland and on either side of the pituitary gland this is a coronal section through the cavernous sinus on either side of the pituitary gland is the cavernous sinus in blue and in the lateral wall or cranial nerves 3 4 v1 and v2 and in the middle of the cavernous sinus

is cranial nerve 6 and the internal carotid artery now the cavernous sinus communicates with the facial vein and pterygoid plexus of veins in addition to draining into the sigmoid sinus so what we see here in this lateral view is there's our cavernous sinus and most of the time blood drains down through the inferior petrossal sinus into the sigmoid sinus and into the internal jugular vein however these superior and inferior ophthalmic veins that are draining the orbit also drain anteriorly to the facial vein so these ophthalmic veins blood because these drove in the sinuses lack valves

blood can go back to the cavernous sinus or sometimes down the facial vein this is important because if as an infection in the orbit or the nasal region that infection could spread through this facial vein through the ophthalmic veins into the cavernous sinus and now you have an infection inside the skull the pterygoid plexus of veins are these veins are in the uh right along the the pterygoid um muscles and these these plexus this plexus of veins in the oral cavity could also communicate down through the retro mandibular vein but also go up into the

cavernous sinus if you have an infection in the oral cavity okay all dural venous sinuses ultimately drain into the internal jugular veins so here's that picture and all of those draw venous sinuses ultimately are going to drain into this internal jugular vein so that brings us up to the circulatory system in the brain so there's your brain it needs blood and so our heart is what's going to pump blood to the brain so the heart pumps blood through the internal carotid invertebral vertebral basal or arteries and those then divide into cerebral arteries like our anterior

middle and posterior cerebral arteries the pica and so forth those cerebral arteries branch and branch and also become arterials which then drain into capillaries now what makes the brain capillary so unique is that there's the blood brain barrier the endothelial cells make these tight junctions along with support by those astrocytes they make it very there's very controlled environment between the internal surface of the capillary and the parenchyma of the brain now capillaries drain through venules and venules ultimately go to become cerebral veins and cerebral veins all of them drain into dural venous sinuses which then

ultimately drain into the internal jugular vein which then brings blood back to the heart and you do this whole process again circulate so the two things that are very unique at this point is the blood-brain barrier very very controlled capillary beds and also the dural venous sinuses which are the separation in the two layers of the dura and these sinuses are lined with endothelial cells but they lack valves let's now go to the arachnoid mater okay so the arachnoid mater is the middle layer of the meninges and it drapes over the brain and the spinal

cord so there's the arachnoid mater right there okay draping over the brain and arachna means spider-like like arachnophobia and are afraid of spiders and modder means mother so that when we take a look at this that this connective tissue that connects the arachnoid to the pm modder kind of looks like a spider web it's spider web like um and so the space below the arachnoid monitor anatomists are like well what do we call it why don't we call it the space below the arachnoid mater the sub arachnoid space sub means below and the subarachnoid space

is filled with cerebrospinal fluid which surrounds the brain and spinal cord so here's a coronal section there's the arachnoid mater there's the subarachnoid space and it's filled with cerebral spinal fluid that is surrounding the brain and the spinal cord it's also csf inside the spinal cord as well so the arachnoid motor the arachnoid granulations is where the csf drains from the subarachnoid space into the superior sagittal sinus there's a subarachnoid space it's filled with csf and the csf then flows into these arachnoid granulations which then filter blood into the superior sagittal sinus and that's how

we get csf back into the circulatory system now let's talk about pia mater now the pia mater is there okay and pia is latin for soft and mater is mother it's called soft um mother because the pia mater consists of loose connective tissue or areola or connective tissue and it is the deepest layer of the meninges intimately associated with the brain and spinal cord so there we can see it all close right along the brain and you see it following the contours of the gyri and sulci and even the blood vessels it makes it surrounds

the blood vessels and makes a connected tissue sheath as those blood vessels dive into the parenchym of the brain so here's just a little schematic of the brain and there's pia mater oh there's the pia mater hugging the contours of the brain where in contrast to the arachnoid mater more like drapes the contours of the brain and between the arachnoid and pia mater that's the subarachnoid space filled with cerebral spinal fluid and that my friends are the meninges and dural vena sinuses in a nutshell [Music] um [Music] you