the third ventricle is on the midline and it is pictured here right in here on the cast and
here this area on the cadaveric brain it's very hard to see the third ventricle when you cut the
brain in half because it's very very thin its walls are formed by the diencephalon which is
this area of the brain and here the hypothalamus and the thalamus we'll talk a lot more about these
structures when we talk about gray matter and cortex and some other deeper structures but for
now they form kind of a narrow cave a narrow cavity for that that is your third ventricle
the lateral ventricles as we've already talked about empty into the third ventricle via the
interventricular foramen cerebral spinal fluid then flows out of the third ventricle via the
cerebral aqueduct into the fourth ventricle I want to bring your attention to this little
midline structure here which corresponds to this little circle or this kind of a negative space in
the cast this is called the masa intermedia and the masa intermedia is simply a lump of
neurons that holds your - the two hemispheres of your thalamus together so your thalamus sits
in the middle of your brain deep deep deep in the middle of your brain and it's two kind of potato
we like or fist like structures and there's one on each side but just in the middle there's this
little bridge of cells and it's called the Masa intermedia we can assign no specific function to
it but it makes this area here that you can see when you cut it and it makes this kind
of negative impression in a ventricular cast the fourth ventricle lies here and it's underneath the
cerebellum so here's our cerebellum squirrly here and here's our fourth ventricle again a cerebral
spinal fluid flows into it from the third through the cerebral aqueduct into this fourth ventricle
it's also on the midline now cerebral spinal fluid this is the last stop for cerebrospinal
fluid on the midline in the ventricular system it exits through three phenomena there are what
there is one foramen of Magendie on the midline note the alliteration Magendie and midline and
there are two lateral foramen the foramen of Luschka and these are the areas these little
tiny foramen are how the cerebrospinal fluid gets out of the ventricular system and into
the subarachnoid space first I'm going to talk about the choroid plexus the choroid plexus we
can see here it's this lumpy stuff it kind of looks if you put it on a histology slide
it kind of looks like a bunch of grapes it's a cuboidal simple cuboidal epithelium there's
a blood supply to it and that eats how it makes cerebrospinal fluid it's kind of like a little
filter cerebrospinal fluid is actually very like plasma it contains a lot less protein it contains
no cells really to speak of if there are cells in your cerebrospinal fluid you are one sick puppy
it usually means that you've got some sort of infection and you've got white blood cells that
have infiltrated and that is definitely not a good thing so the choroid plexus is in all of
the all of the ventricles it's indicated kind of by this pink here in the cast we painted it pink
to indicate that there's choroid plexus there but it's in all of the ventricles again on this
image you can see here's that anterior horn of the lateral ventricle here's the posterior horn of the
lateral ventricle and here's the body so you can see the full range of the extent of that lateral
ventricle and you can almost I wish if I was a bug and I could just travel down through this
little gap then you'd be traveling down toward the midline and into the third ventricle so
the flow of CSF we're going to review in the next slide so again we have our two lateral ventricles
lateral ventricles we've got the ant your horn the inferior horn posterior horn Trigone and
body you've got third ventricle and the fourth ventricle so cerebral spinal fluid is made all
through here okay all through these ventricles and then it exits through the interventricular foramen
into the third from the third to the cerebral at through the cerebral aqueduct into the fourth and
then oh I already wrote that and then out through a to foramen of Luschka and one midline foramen of
Magendie and then it goes into the sub arachnoid space once it's in the subarachnoid space that's
where it's doing its main work where it's floating your brain so that your brain doesn't squish your
brainstem it doesn't squish the blood vessels that are coming up through the neck and into
the base of the skull and it doesn't squish your cranial nerves which are leaving your brainstem
to go out and innervate things in your face and your head and neck so it's very important that
you have CSF if you have too much we call it hydrocephaly and it can happen hydrocephaly can
actually occur during fetal life or in a neonate sometimes the cerebral aqueduct is too narrow and
it cannot escape and so it keeps being formed and then presses up against the outside of the skull
and if it's before the fontanelles have closed you end up with the the typical appearance of
that very large cranium these days were very good at diagnosing and very good at catching anything
like hydrocephalus when it's very very early and they put in what's called a shunt and so that the
extra CSF can exit the system and go harmlessly into the abdomen they'll run the shunt all the
way down into the abdomen and that way you have just enough CSF but not too much and you don't
squish the brain again how this is the way that one sits in this subarachnoid space how we get
it resorbed the arachnoid granulations pushing into that dural sinuses side of circulation but
I want to bring up at this point is the fact that the choroid plexus and the arachnoid granulations
for some odd reason I don't know why don't talk to one another so you get a constant
creation of cerebrospinal fluid by the choroid plexus and a constant absorption of CSF by the
arachnoid granulations and so usually that's imbalance usually that's just fine and your
your brain is floating and everybody's happy but every now and then like I said if there's
a blockage somewhere something has gone wrong in like the cerebral aqueduct or maybe one of the the
Foramina of Luschka or Magendie and it can't exit you get a buildup within the brain and then and
then the brain will be squished there are also other things like inflammation if there's been
something like meningitis and the arachnoid granulations become inflamed they may become
slightly scarred and Cerebal spinal fluid can't get out of the arachnoid granulations back into
the venous blood flow so those are bad things and we always try to keep a very close eye on
those kinds of thing we I'm not a clinician the neurology people keep an eye on that kind
of stuff to make sure that that doesn't happen so in summary what I want you to know is how
many ventricles there are what are their names and specifically with that lateral ventricle
no which part which horn is in what part of the cortex where is cerebral spinal fluid made and who
makes it how does cerebrospinal fluid circulate through the ventricles so be able to trace that
entire path and then once cerebral spinal fluid is out out of the ventricular system where does
it go at subarachnoid space and then how is it absorbed out of the subarachnoid space into the
venous circulation if you know all of these kinds of things then you're ready to take assessment