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Student and Therapist Newsletter Archive
- Ventricular System
+ Why is the ventricular system so important? - January
07
Hi John,
I am being repeatedly told that the ventricles are very important but
I am not sure why. I have asked this question of my tutors repeatedly
but never got a satisfactory answer. I would be grateful to hear your
explanation.
Thanking you in anticipation.
PB
South Africa
>>>MY COMMENTS:
It may be easier for you to think of
the whole system in terms of plumbing, which it is in a way.
It's a very important and significant plumbing system.
The ventricular system, is a collection of cavities and canals
deep within the brain and spinal cord. It consists of 4 ventricles connected
by various channels. It always looks to me like a model of a space
ship.
Think Star Trek.
The four ventricles are made up of the 2 lateral Ventricles
located within the two cerebral hemispheres, each of which connect via
an inter-ventricular foramen to the 3rd ventricle which is located between
the two thalami of the brain.
The 3rd ventricle connects inferiorly through the cerebral
aqueduct (or aqueduct of Sylvius as you will see it in some books) to
the 4th ventricle which is located between the cerebellum, posteriorly
and the pons and medulla, anteriorly.
The 4th ventricle continues inferiorly as the central canal
passing down the centre of the spinal cord.
The whole ventricular System is filled with Cerebrospinal
Fluid.
So that's the plumbing. Now let's look at inlet
and outlet valves.
The INLET valves are located in the roof of each of the four
ventricles and are called Choroid Plexi. These are filter like structures
through which cerebrospinal fluid is formed as a filtrate from arterial
blood. Arterial blood enters the choroid plexi from the cerebral
arteries; then blood cells, proteins and other large particles are filtered
out. The pure colourless fluid that filters through this choroid
plexi into the ventricular system is cerebrospinal fluid.
I will get to the outlet valves in a minute.
First I want to focus on something that is very easy to get confused about.
We know that the membrane system contains cerebrospinal fluid,
right?
Just nod.
And now we have a good idea of how cerebrospinal fluid enters
the ventricular system.
And we also know the ventricular system is contained within the membrane
system. The thing is the ventricular system is, for the most part,
closed.
So how does cerebrospinal fluid get out of the ventricular
system into the membrane system?
Very good question. It all happens in the 4th ventricle.
In the posterior and lateral walls of the 4th ventricle there are three
foramina, - the foramen of Magendie which is in the middle posteriorly
and the 2 foramina of Luschka, bilaterally.
It is through these 3 foramina that cerebrospinal fluid passes
out into the sub-arachnoid space where it circulates around the brain
and spinal Cord.
Now back to the OUTLET valves.
Cerebrospinal fluid is eventually returned to the blood via
the Arachnoid Villi which protrude from the sub-arachnoid space through
to the superior sagittal sinus of the Brain. It re-joins the venous
blood which then drains from the venous sinuses via the internal jugular
Vein to be returned to the heart.
So that's the plumbing, the general flow and the
inlet and outlet valves. The significance is that this system
is in continuous use which means
it has to be in working order all the time. If any one of the valves
or canals of foramina are not working properly the effects are serious.
Just think of the person having a spinal tap.
Only a tiny amount of cerebrospinal fluid is removed yet the person will
have to lie horizontal for 24 hours to avoid severe headaches.
Also if there is a problem in this system it's not like you
can just shut it down while repairs are made.
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