hello friends it is dr. Alsup here and we are going to spend the next few minutes discussing
the ventricles of the brain and what they secrete which is cerebrospinal fluid so major
learning objectives for this session include defining cerebrospinal fluid CSF so what does
it do where is it located where is it secreted from so we'll we'll cover all of that as well as
discussing the ventricular system which are really just hollow spaces within the brain alright so
let's talk cerebrospinal fluid CSF is composed of substances from blood plasma it's primarily
water but there are other substances and there as well these are going to it's going to be secreted
by what's referred to as choroid plexuses and these are networks of modified blood capillaries
that are located in the walls of the ventricles so these pink areas on this ventricular model
are supposed to be representing the choroid plexuses CSF will be located in the ventricles as it
is secreted but it will also circulate slowly and continuously in the subarachnoid space that space
that is going to be between the Pia mater and the arachnoid mater so this is a subarachnoid
space here functions of the CSF include shock absorption so think helping the brain not hit
the bone with movement it's going to help kind of reduce that weight of the brain and
it's also going to provide an optimal chemical environment for neuronal signaling okay so let's
talk ventricles I've always a little bit amazed by ventricles because they're literally spaces within
the brain where CSF is produced and through which it flows to get towards the subarachnoid space
it's also where within those walls you'll have those choroid plexuses which is the site of CSF
CSF formation excuse me okay so let's talk about the ventricles there are four ventricles there
will be two lateral ventricles which your first and second ventricles and these occupy a fairly
large area within the cerebral hemispheres and you can see in this corpus callosum region here
this little dark area where you're entering into the hollow lateral ventricle CSF will drain from
the lateral ventricles into the interventricular foramina of which there are two so one for each
lateral ventricle so they will go from the interventricular foramen ah into the third
ventricle the third ventricle will be located in the middle of the diencephalon so this is one side
of the diencephalon the other side would be on the other part of the Hemisected brain you put
those together in that space in between would be the third ventricle the third ventricle is going
to drain via the cerebral aqueduct into the fourth ventricle which lies between the brain
stem so posterior to the brainstem and here is the cerebellum here so this will be your
fourth ventricle you can visualize the flow from the lateral ventricles on with all these really
nice arrows that I've created so you can see lateral ventricles into the interventricular
foramina-- into that third ventricle the third ventricle the CSF will flow through the cerebral
aqueduct into the fourth ventricle and I want to focus on this area right here what happens after
the fourth ventricle so it can do one of four things that the CSF can do one of four things it
can continue into a remnant of the ventricular system of the spinal cord referred to as the
central canal so not a large amount of CSF is going to head actually within the spinal cord
region more CSF really the majority of it will enter the subarachnoid space so that's kind of
key here is the rest is really going into that subarachnoid spaces so it can do this via the
median and lateral apertures which are located in the wall of the fourth ventricle so this allows
that CSF to flow in the subarachnoid spaces now I can go in into the subarachnoid spaces of the
cerebellum and around the cerebellum in the spinal cord and also CSF can exit the apertures to flow
into subarachnoid cisterns which are just larger areas of the subarachnoid space this will I'll
see us have to kind of flow in the subarachnoid spaces of the more superior portions of the brain
this is just a cartoonish illustration of the previous flowchart the shaded area whoops excuse
me whew I'm going too far ahead I'm very excited all right so the this cartoonish illustration
this area right here these kind of shaded in regions are showing where the ventricles are
so you have your lateral ventricle here you can see how large it expands you can see it expanding
all the way into this region here is your third ventricle flowing through the cerebral aqueduct
to get to your fourth ventricle and you can see this central canal that is moving in to
or within the spinal cord or you can see these holes right here which represent the apertures
so how it's getting into the subarachnoid space to either go through around the spinal
cord region around the cerebellum and then up into the subarachnoid space up here all right
now when CSF needs to be recycled it drains into the venous system specifically into those dural
venous sinuses and it will enter the sinuses through arachnoid granulations so this is an
area in the subarachnoid space or this is the area with the subarachnoid space we see yourself into
it and this highly folded complex of arachnoid mater so subarachnoid space here is arachnoid
that is highly folded moving into this region into certain dural venous sinuses in particularly the
superior sagittal sinus and when it does this it allows for CSF to drain into the venous this you
can even see in this illustration how there's often a close relationship here to the bone so
where those arachnoid granulations are getting fairly close to the bone which can cause erosion
or pitting of the bone in those regions referred to as granular foveolae I wanted to bring up this
term lacunae or lacunae if we're talking about plural because these are fairly obvious when
looking at some of these larger venous sinuses particularly the superior sagittal sinus so here's
your superior sagittal sinus which is extending all the way right here all that the lacunae are
our lateral expansions of the venous sinuses so you can see that here here as outlined you
can even receive extending kind of further out in this region so these are important because these
are a common sight for arachnoid granulations to extend into so it's not just directly into
the main part of the superior sagittal sinus it could also move into these lacunae which are the
lateral extensions of the dural venous sinuses all right this wraps up our conversation of the
ventricles and cerebral spinal fluid let's take a minute to review a concept before we finish okay
question a blockage in the cerebral aqueduct would prevent flow of cff CSF excuse me into
which ventricle is it a lateral ventricle B third ventricle C fourth inch ventricle all
right so the correct answer here is going to be C the fourth ventricle the cerebral aqueduct is
between the third and the fourth ventricles if you had some form of blockage within the cerebral
aqueduct that would not allow flow into the fourth ventricle so preventing that flow you could have
a backup of CSF into the ventricles recall that the interventricular foramena is going to be
but you'll have two of those and those will allow for CSF flow between the lateral ventricles and
the third ventricle all right so that should be all for this lecture after you have reviewed if
you have any questions please do feel free to reach out thank you for your time and attention