in this demonstration I'd like to talk about the ventricular system and before we talk about the
ventricular system in the adult brain I want to talk a little bit about how it gets how it gets
to where it is so your brain and your spinal cord your whole CNS start out as a flat plate
that flat plate rolls up into a tube the hole in the middle of that tube remains throughout
development and into the adult brain and spinal cord and we call it the ventricular system in the
spinal cord it's simple because the spinal cord is kind of like just a long band of cells along
column and then the tube is in the middle and we call it the central canal and then in the brain it
gets more complicated because the brain as you can see is you know pretty busy place and it's
curved you can see from the corpus callosum from the corpus callosum that it is curved and that
the cortex is curved this results in the curvature of the ventricles okay you'll also note that you
have two one on each side this is the result of your brain when it develops let me grab this it
develops into two hemispheres because it starts kind of as a tube and then the middle of the
tube gets pinched and gets anchored and then the resulting pieces grow like two giant bubbles and
those two giant bubbles turn into well these don't match but this one's closer they turn into your
two hemispheres so you have two cortical bubbles which make your two cerebral hemispheres and since
you have two bubbles you have two ventricles one on each side so the lateral ventricle is the main
ventricle that you're seeing here in this cast so this is kind of a negative this is when we pump
some plastic into the brain and there and then peel the brain away we're left with this cast of
the hole in the middle and so let me go through this slowly and then I'll point out in some of
the brain specimens where these things are in an actual brain so this is the lateral ventricle it
has an anterior horn which is in your frontal lobe it has a posterior horn and when this is inside
your occipital lobe it has an inferior horn and this is in your temporal lobe they all three kind
of come together here in an area called the Trigone looking from the front you can see it curved down
in front into the frontal lobe and because this is from a real brain it's not exactly a mirror image
because nothing is completely symmetrical if we look from the side you can see that both of the
lateral ventricles drain into a midline structure called the third ventricle and so everybody says
well why do you have why does it start with the number three well nobody could decide which one
was one and which one was too left or right it's kind of like left and right Twix you've got left
you've got a left lateral and a right lateral and nobody cares which ones one or two but it still
leads to the one in the middle being three so the third ventricle is on the midline the lateral
ventricles both drain into the third ventricle you know in a brain it's it's a hollow structure but
here it's obviously it's the solid the solid canal here is called the interventricular foramen you
may hear it called the interventricular foramen of Monroe but we're trying to move beyond eponyms and
simply call things what they really are because then they make more sense so the interventricular
foramen drains from the lateral ventricles into the third the third ventricle then drains into the
fourth ventricle via the cerebral aqueduct which you can kind of see here and I'll show you these
things on real brains the fourth ventricle then opens up into the subarachnoid space now why are
the ventricles so important the ventricles contain cerebrospinal fluid and that probably didn't when
I was talking about draining that probably didn't make any sense until I said cerebrospinal fluid
because that is what is in the ventricles and that's what's draining from lateral to third and
from third to fourth so cerebral spinal fluid is generated by a structure called the choroid plexus
and i have some examples of that that i'll show you and then cerebrospinal fluid gets out of the
ventricular system into the subarachnoid space via three little foramina which exit from the
fourth ventricle and you can't really see them but you have a one on the midline which is the
foramen of Magendie and two laterally which are the foramen of Luschka and I wish we had better
names and not eponyms but that's still what they're called okay so I'm gonna set aside the
model and I'm gonna show you what the ventricles look like and excuse me unreal brains so yes one
thing I need to also point out on the midline the two lateral ventricles are separated by the
septum pellucidum in this specimen you can see part of that septum pellucidum here and I'll
show you on some of the other brains where it is in a horizontal and in a coronal section so
if you remove this septum pellucidum then you can see deeper into the lateral ventricle and you can
just kind of see a window here and deep in here is the lateral ventricle okay yes on this brain
we've detected away some of the other structures we've detected away the dissector away the brain
stem and the cerebellum and you can see a lot more of the extent of the lateral ventricle going deep
and the third ventricle is really interesting because it's a midline structure and its walls
are formed by this area called the diencephalon once you cut the brain you kind of lose the third
ventricle but I can show it to you on a horse are a coronal section in a coronal section sorry just
an aside these brains all you'll notice I'll have tags and little strings it's because we're
very serious about keeping track of all of our anatomical specimens because they are real brains
from real people and we really need to keep track of them so we give them all the label here is the
third ventricle so when you cut it you can see when you cut down the midline you can see that
the lateral ventricles are off to the side here's that septum pellucidum I was talking about in the
middle that separates the two and then here's the third ventricle and it's smack on the midline so
when you cut through it you kind of lose it so we talked about the fact that you have an anterior
horn a posterior horn and an inferior horn and I want to show you how those look in other pieces
of the brain okay this is an anterior section of the brain so this is your frontal lobes right here
and the reason I know that is because I've got the leftovers of my olfactory and I have this little
gyrus under here called the gyrus rectus so it's really straight so if I flip it over so you can
see on inside here's that anterior horn of the lateral ventricle you can see a dead ending here
in the frontal lobe and again septum pellucidum and this is what the corpus callosum looks like
in cross-section you've seen it going this way and a lot in the sagittal brain and this is it
in a cross-section okay towards the middle of the brain this is more anterior so it's a little bit
more this is an anterior sections of the brain if you were looking at the sagittal this is taken
this section is taken at about here because I can just see the frontal pull here and here so this is
the front and here's our lateral ventricle again septum pellucidum going just a little bit farther
back because this is a thick section we can see still we can still see the lateral the septum
pellucidum and the third ventricle and we can see that inferior horn which is just here so that
inferior horn that goes down into the temporal lobes this one so we've got the lateral and now
we've got just a little bit of this inferior horn down here in the temporal lobe so that's
right there so lateral third and then in for your horn of the lateral this is kind of still anterior
hornish late area once we get all the way to the back of the brain into the occipital lobe we can
see the posterior horn and that's this part here in the posterior lobe now the brain because it's
curved you have to get you have to kind of close your eyes and use your 3d thinking cap and think
about how things are curving and what you might see if you cut in different planes so if we cut
the brain straight straight through the middle then we can see a sagittal part of the brain it's
called a sagittal mid sagittal cut and we can see the corpus callosum and a window into the lateral
ventricles when we cut the brain from front to back it's called a coronal section like a crown
over your head that is when we get this view of the two lateral ventricles and we see other other
structures that we'll talk about in a later demo if we cut the brain horizontally we're cutting
this way through the ventricle system and because it's a curve will see the different ventricles in
two different places and that's what we see in this section this is a horizontal section of
the brain this is the front this is the back and here again is that anterior horn of the lateral
ventricle this area is the third ventricle and here is the posterior horn of the lateral
ventricle now we talked about the fact that the lateral ventricles are where your cerebrospinal
fluid is made it's made by this funny-looking little epithelial material called the choroid
plexus you can see it here I think you can see it nope you can see a little bit of it
here going back this way and I think those are my best examples so here and here this choroid plexus
actually does exist in all of the ventricles and it is it creates cerebrospinal fluid and
cerebrospinal fluid is an ultra filtrate of plasma so it's kind of like plasma but it has different
ion concentrations and it's what we measure when we suspect a brain infection they will measure the
cerebral spinal fluid and look at it to see that there's any kind of inflammatory response like
um white blood cells if there's white blood cells in your CSF you are one sick puppy so anyway this
is the choroid plexus and it exists in all of the ventricles and it makes cerebrospinal fluid
cerebral spinal fluid gets out again through those three phenomena in the in the fourth ventricle the
two laterals of Luschka and the medial Imogen and then it floats out in the subarachnoid space
and I can't really demonstrate the subarachnoid space I'll have another demonstration that'll
show you a little bit more of them in in Gees but the bottom line is this is the arachnoid
and in life it's suspended it more it looks more like a sponge than a flat layer and it's full of
cerebrospinal fluid cerebrospinal fluid is made at a constant rate by the quarry plexus and absorbed
by these little kind of cauliflower looking things on the top called arachnoid granulations
and i'll have some better pictures of these and some diagrams in the lecture that you'll
that you'll see but the arachnoid granulations then absorb the cerebrospinal fluid so there's
constant production constant absorption and the CSF quite literally floats your brain in your
skull if it didn't then your brainstem and the base of your brain would collapse onto the base
of your skull and squish the blood vessels that are coming in squish your cranial nerves and it
wouldn't it would be bad it would be very bad so cerebral spinal fluid is created by the quarry
plexus absorbed by the arachnoid granulations and floats your brain and keeps everything from being
squished lateral ventricles third venture I'm sorry excuse me let me make this so again lateral
ventricles you have to a left and a right third ventricle cerebral aqueduct fourth ventricle oh
yes that reminds me one of these specimens has a very good yes this way there's a very good
cerebral aqueduct in fourth ventricle on the sagittal brain you can see again the lateral
ventricle and the interventricular ventricular for riemann right here and the third ventricle
which is kind of lost because again where it's a midline structure and it's very thin and when we
cut it we lose it this tiny little gap here this kind of little canal is the cerebral aqueduct it
leads then into the fourth ventricle which is right underneath your cerebellum okay so
lateral ventricles off to the you know deep to the to this third ventricle interventricular
foramen cerebral aqueduct fourth ventricle and then it goes out from little fir Aminah in here
to the subarachnoid space and that concludes our demonstration of the ventricular system