hello anatomy friends this is dr alsup and in this video we will be discussing the ventricular
system as well as the cerebrospinal fluid or csf developed within the ventricular system and
we've discussed the cerebrospinal fluid before when we were discussing the subarachnoid space
associated with the spinal cord but now we get to explore where it actually develops and how
it will flow in order to reach that subarachnoid space and this is through that ventricular system
so i always think the ventricles are hard for students to conceptualize because they often
try to make them solid structures and i think for good reason because they're looking at models like
this one but this model is actually showing the general shape of the space and that is the key
word here is the ventricular system consists of spaces and connecting channels that are lined with
epidermal cell or those supporting cells so these ventricles and connecting channels are going to be
derived from the central lumen of the embryonic neural tube and the key is these are spaces
and it is in the walls of the ventricles that cerebral spinal cerebrospinal fluid hard to
say is produced and you can kind of see this represented here in this image in pink it's these
are representing the choroid plexuses that are on the walls of the ventricles and that is where
um cerebral spinal fluid will be produced and it will make its way to the subarachnoid space in a
set direction and that's where all these arrows kind of come into play we'll get into that a bit
so let's talk a little more about these ventricles there are four ventricles that are all connected
or they're going to be connected in a set direction and we will start with the most
superiorly located which are the paired lateral ventricles so these could be called the first
and second ventricles but they never really are you'll always almost always hear lateral
ventricles and these are going to be located or these are spaces within the cerebral hemispheres
and it's going to have this very distinct c shape with some horns associated with it so i'm
outlining this so you're going to have the body which is the main portion then you'll also have an
anterior a posterior and an inferior horn of the lateral ventricle so in each lateral ventricle
both lateral ventricles will drain csf via the interventricular foramina so there'll be one
for each lateral ventricle which this is very often hard to distinguish but it's going to be
this connection between the lateral ventricle and the third ventricle the third ventricle is going
to be located in the midline of the diencephalon so a space and portions of the thalamus and the
hypothalamus it's going to be this kind of oddly shaped region right here and the third ventricle
will um be connected to the fourth ventricle by the cerebral aqueduct
which generally is a little bit longer certainly in comparison to the interventricular foramina
it will run through the midbrain region and will connect to the fourth ventricle
it is the fourth ventricle that is going to be located between the brain stem specifically the
pons and the medulla and the cerebellum so it's this general area right here
and the fourth ventricle can also be considered the last ventricle or the more distal ventricle
and from here the majority of csf moves into the subarachnoid space so that subarachnoid space is
key here it will do so v via small holes or openings or apertures in that ventricular wall
although a small amount will also continue into the central canal of the spinal cord so within
the actual spinal cord the central canal is a vestigial remnant of the ventricular system
of the spinal cord and it kind of just peters out the more distal you get on the spinal cord
but as the majority of csf moves into the subarachnoid space from the ventricular
system let's focus a bit more on those there are three main apertures that allow csf to move from
the ventricular system to the subarachnoid space this this will include the single
or unpaired median aperture and you can see that kind of in this general region right here and then
you will also have the paired lateral apertures so two and three to get to the three apertures
so you can only see one on this hemisection here there would be a matching one on the other side
and all three of these apertures are going to lead into what are referred to as subarachnoid cisterns
which really are just more expansive or larger subarachnoid spaces so that pia mater is always
going to be really closely adhered to the um to the brain so that will always be the case
but in certain regions the arachnoid mater is more tinted over and more
widely separated from the pia mater making a naturally occurring larger subarachnoid space
referred to as a subarachnoid cistern and you'll have them kind of throughout
the areas surrounding the brain so that's just a few right there for our purposes you don't have
to know the specific names of the subarachnoid cisterns you may in other parts of the curriculum
again these um subarachnoid cisterns are subritenoid space they are continuous with the
more generalized subarachnoid space that surrounds the entirety of the central nervous system
including around the spinal cord now don't forget that while i think we likely have it down at this
point that csf is flowing within the subretinoid space neurovasculature is also located in this
area so the blood supply for the brain as well as cranial nerves will be within this region
now let's talk a little more about how csf is formed these are going to be formed by
what's referred to as choroid plexuses so anytime you're looking at any of these images
it's often shown as kind of a reddish color these are found in the walls of all the ventricles
and they are going to kind of show up as these pinkish or reddish structures because they're very
highly vascularized and it is from the choroid plexuses that the csf is secreted the flow of csf
is a proximal to distal or superior to inferior to make its way to the subarachnoid space and it
is continually being produced and being replaced meaning that older csf needs to be removed from
the subarachnoid space and it will do so by being reabsorbed into the venous system and this is
possible from by what's referred to as arachnoid granulations so you see kind of right here a few
illustrations of what that is and basically these um arachnoid granulations or villi when
you're talking about younger individuals these are extensions of subarachnoid and subarachnoid space
that project into the dural venous sinus and allow for the csf to drain into or be
reabsorbed into the venous sinuses artenoid granulations are associated with quite a few
dural venous sinuses but are most frequent and most easily observable with associated with the
superior sagittal sinus that sinus that's running along the superior portion of the falx cerebri
now in certain pathological conditions there can be an abnormal accumulation
of csf within the ventricular system leading to enlargement of portions of the ventricular system
so blockages or obstructions that can occur are most common
uh commonly associated with those narrow channels or foramina so between the different ventricles
or to allow movement into the subarachnoid space and a blockage would most greatly affect the size
of the ventricles or the ventricular spaces more proximally so say there's a blockage
in the inter intervertebral foramina kind of in this region here that would most greatly affect
the lateral ventricles and less so in terms of the more distal ventricles if you had a
blockage of the cerebral aqueduct that would most greatly affect both the lateral ventricles and the
third ventricle because those are going to be more proximally associated and if you had a um
a blockage in any of the apertures or those foramina associated with the fourth ventricle
that could affect the whole ventricular system hydrocephalus doesn't have to be caused by a
blockage of one of those channels it could be associated with ineffective absorption of csf
excellent we have made it to the summary slide please use this slide as a study guide and means
of consolidating your knowledge on this topic as always please feel free to reach out with any
questions to me or any of my anatomy colleagues and i thank you for your time and attention