CSF in an uncomplicated way

we will be learning about Cerebrospinal Fluid in this article :-

Well apart from Blood , Lymph and Tissue Fluid there is an another fluid system in our body particularly associated with the central nervous system and that is the "cerebrospinal fluid"

Now the Question is why does our CNS needs an seperate fluid system ? although brain and spinal cord has a profused blood supply (about 15% of cardiac output actually goes to CNS)

Well Frankly speaking the answer is pretty much disputed among the researchers but you will get an idea about its need by looking at his functions

Functions of the CSF :-

• Protect brain and spinal cord from trauma.
• Supply nutrients to nervous system tissue.
• Remove waste products from cerebral metabolism.

Those were the 3 most important functions of the CSF.

CSF is "super interesting" as it is a fluid which is present inside the CNS and also on outer side of the CNS

YAH ! IT IS PRESENT INSIDE THE CNS AND ALSO ON OUTER SIDE OF THE CNS

Wanna know how , Let's start by understanding the flow of CSF inside the CNS first than we will be looking at outside flow of CSF

Ventricle system of brain

let's start with the basics you might be knowing that our brain contains fluid filled big spaces called "Ventricles" {Ever heard of them!}

look at the image below to understand what i said in upper paragraph :-

see the blue part they are the ventricles

Those fluid filled spaces are the ventricle of brain and the fluid which is filled over there is nothing but the "CSF"

There are 4 ventricles in the brain - Two lateral Ventricles , third ventricle and fourth ventricle

Look at the image below to get more understanding about the ventricles :- (it is a saggital section and you are looking from anterior side)

Carefully follow the text by relating it with the upper image :-

• Notice Above the midbrain the area coloured red actually shows the lateral ventricles
• Area of ventricle filled with purple colour - "Third Ventricle"

Note - Lateral Ventricles are connected with the third Ventricle though two foramen named as foramen of monro (see the marking "a" in the above image)

• Area of ventricle filled with yellow colour - "Fourth Ventricle"

Note - Third Ventricle is connected with the fourth ventricle through a duct known as Cerebral aqueduct of Sylvius (see the marking "b" in the above image)

Fourth Ventricle is continued in spinal cord as central canal.

so let's get a fast review of what we learnt so far:-

1. ventricle - CSF filled spaces inside the brain.
2. There are 4 ventricles inside our CNS - 2 lateral ventricles, 3rd ventricle, 4th ventricle .
3. Lateral Ventricle is connected with 3rd ventricle of foramen of monro .
4. 3rd ventricle communicate with 4th ventricle via cereberal aqueduct .

IMAGE SHOWING THE VENTRICULAR SYSTEM OF CNS :-

Do you remember i said in starting - "CSF is "super interesting" as it is a fluid which is present inside the CNS and also on outer side of the CNS"

Now as we are done with internal flow path of CSF in the CNS , let's talk about the path of CSF on the outer side the CNS

Our brain is important Vital organ so there are 3 meninges (protective layer) outside of it named as

1. Duramater (present most externally)
2. Arachnoid mater
3. Pia mater (present most internally and in close association to brain)

Look at the Diagram below to have a more clear understanding :-

Look carefully in the above image :-

• Purple colour marks the piamater lining , note carefully that Piamater is very Closely associated with the brain substance and there is no space between the piamater and brain substance
• Green Colour line marks the arachnoid mater , note carefully that Arachnoid is not very closely associated with the piamater and it leaves a very big space in between known as - "Sub Arachnoid space" (sub-below ) Space is coloured grey in the above diagram
• Red colour marks the Duramater lining , note carefully that Duramater is the outermost lining and it also leaves a space - "Sub Dural space"

now why i discussed them ? i did that because Sub Arachnoid Space is that space which is actually filled with the CSF

Yeh ! ;) so as we can understand that the Sub Arachnoid space is present on outer side of CNS and it is filled with the CSF , that's why i said that CSF surround CNS on outer side too.

see the image below for a more clear understanding:-

so long story short - CSF is present in the Ventricles and also in the subarachnoid space

Now we have to learn two things more to finish the topic -

1. Who actually produces the CSF?
2. How the CSF in the Ventricle and CSF in Sub Arachnoid space Communicate and what is the actual flow path of the CSF ?

Production of CSF:-

Spoiler alert !! it is produced by choroid plexuses , this is what every book mentions ... But what are they ? lets understand their concept :-

Before learning about them we must be aware with some terms let me make you aware with some important terms

• Choroidal artery :- these are arteries which are having two divisions - posterior choroidal artery (arising from posterior cerebral artery) and anterior choroidal artery (arising from Internal carotid artery)
• Epindyma :- you know endothelium is inner lining of blood vessel , just like that the inner most lining of the ventricle is "Epindyma" so when ever you imagine the space filled with CSF (Ventricle) within the CNS you must know that the cells which are covering the ventricles on interior part (which is in contact with CSF) are actually a part of epindyma and combined together they form a covering called "Epindyma"

wait !! what are those cells which are actually forming the epindyma ?? can you guess ??

let's talk about them a little bit so i want to ask you which cells are present in the CNS ? Anwer is pretty much straight - Neurons and Glial cells

So it is actually the Glial cells which forms Epindyma (see their name implies the same meaning Glia=helper)

Lets learn now about the production of CSF:-

CAREFULLY OBSERVE THE IMAGE POSTED BELOW :-

The image above is actually a simplified cut structural diagram of lateral ventricle (seen in saggital section you are observing it from front )

Look at the Foldings made by the choroidal artery --- Actually choroidal artery enter in the Ventricles and they form several foldings over there (to increase surface area which is in contact ) but this artery does not pierce the Piamater , as you might be knowing that between ventricle and artery is Piamater , this artery does not pierces the Piamater what actually happen is Piamater also move in the ventricle with the choroidal artery and make his folding in a similar way as of choroidal vessels

See in above Diagram Piamater is present on interior side in close association with the choroid vessel ( Noticed in above diagram !)

Also note in the above diagram a Blue Coloured line actual lines the interior aspect of ventricle as well as the piamater (where it is closely associated with the choroidal vessel) that is actually the "Epindyma"

So Let us have a fast recap of what we have learned so far :-

• Choroidal artery move towards the ventricle ---> do not pierce the Piamater rather takes the piamater with him ---> Forms infoldings over there with piamater ----> on interior side it is actually lined by the Epindyma

See Below Diagram for a more clear understanding :-

Now Let us Clear what actually Choroidal plexus is ?

see :-Infoldings of Choroidal Vessel + Piamater Forms "Tela Choroidea"

Tela Choroidea + Epindyma Forms CHROIDAL PLEXUS

So whenever anyone say

• Choroidal plexus it means = Infolding of Choroid Vessel +Piamater + Epindyma.
• Tela Choroidea means = Infoldings of Choroid Vessel +Piamater.

So They in a combined manner secretes CSF we will learn about its production part later on , at first let's learn about the Location of these Plexuses in the Ventricles we learned above :-

• 

• 

From above image it is clear that :- In lateral Venticles Choroidal plexus is found roughly on medial side , in 3rd ventricle it is present on the roof and also in 4th ventricle they are present at the roof.

Little Bit of its Physiology

Production:-

it is a very elaborative process but the main part that you need to know is :-

Cerebrospinal fluid is produced by the choroid plexus, located in the lining of the ventricles. It consists of capillaries (choroidal vessels) and loose connective tissue. Plasma is filtered from the blood by the epithelial cells to produce CSF. In this way, the exact chemical composition of the fluid can be controlled.

Drainage:-

Drainage of the CSF occurs in the subarachnoid cisterns (or space). Small projections of arachnoid mater (called arachnoid granulations), protrude into the dura mater. They allow the fluid to drain into the dural venous sinuses.

What controls the Composition of CSF :-

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Let me tell you that actually in Epindyma there are several pumps which transport different ions from the blood and to the blood . It is again an super elaborative process what we need to remember at this level is :-

Look in the image above and relate the text below

1. Sodium pump :- these active pump efficiently transport the Sodium from the blood to the cavity of ventricle
2. As sodium increases in the fluid of ventricle so does the positive charge there so to maintain charge balance the Chloride ions (with negative charge ) also enter in CSF from the blood .
3. Potassium pump :- These active pump actually transport the potassium from the CSF to the blood . this explains why CSF has a low potassium level as compared to the serum potassium levels.
4. Due to accumulation of more sodium and chloride ion in the CSF osmotic pressure get increased and it pulls the water from the choroidal vessel into the CSF
5. Glucose transporter :- There are Glucose transporter present in epindyma but they are not very efficient so glucose get transported from the blood but not in an great amount so the amount of glucose in the CSF in actually low than the blood

Communication between the Ventricular system and subarachanoid space of CNS

The fourth ventricle continue with the central canal we have already studied that but let me tell you that there are actually three more foramen through which 4th ventricles drain the CSF into the subarachnoid space

I told you that the CSF is produced by Choroid Plexus in the ventricles but what is the source of CSF in subarachnoid space???

Actually there is no production unit of CSF for subarachnoid space it is actually the CSF which is produced in the ventricular system get recycled to subarachnoid space via these foramen present in the fourth ventricle

There are 2 lateral foramen in the fourth ventricle - Foramen of Luschka . and 1 median foramen - Foramen of Magendie

See the image below :-

Imagine you are in the fourth ventricle with your hand expanded(just like sharukh khan) and leg bent than it will be very interesting to note that

• Your both hand touch the foramen of Luschka
• your straight leg will go into central canal
• your bent leg will be going into foramen of magendie

Look the Diagram below:-

So you must be clear now with the communicating canals that help to connect the ventricular system with the Subarachnoid space

so The exact path of CSF is :-

Lateral ventricles --> 3rd Ventricles --> 4th ventricle -->central canal as well as to subarachnoid space via Foramen of Luschka and Foramen of Magendie.

Finally the CSF is drained in Subdural sinuses via Arachnoid granulation(mentioned above ) and at last drained in the emissiary veins which connect with the subdural sinuses

That's all about the Cerebrospinal Fluid and I arrest my case now.

A big thanks for reading the article

Have a nice day.

------------------Bhavesh saini ;)