Decrypting the "Arterial blood supply to CNS"

In this one we are going to talk about the arterial blood supply to the CNS

Let's start with most basic things , let's start with a Question how much of Cardiac Output is actually contributed to CNS?

It is actually 15% and that is a big no. this makes CNS one of the highly perfuesd organ system

So Before starting let me tell you that our brain is actually perfused by two system :- vertebrobasilar system and internal carotid system , we will be talking about them in complete detail but at this moment i want you to remember them as names.

so Basically we divided brain blood supply into two parts :- Anterior part blood supply and posterior part blood supply , let me tell you that the posterior part is actually sypplied by the vertebrobasilar system and anterior part is supplied by internal carotid system.

Before getting into details of blood supply let's understand the basic origin of vessels from the heart so that you can understand which vessel from aorta actually supplies the brain and spinal cord.

See the Image below and Follow the text :-

From arch of aorta there arise major 3 big vessels :-

1. Brachiocephalic trunk
2. left Common carotid artery
3. left Subclavian artery

To make things simple let me tell you that from arch of aorta mainly two vessel system arises :-

• Subclavian system
• Carotid system

so long story short :- the brachiocephalic trunk actually divides into common carotid and subclavian arteries , (YEH! that's strange) so Brachiocephalic trunk itself divides into right subclavian artery and right common carotid artery and left common carotid and left subclavian arteries take a different origin from arch of aorta

So in short we have now 4 major vessel from arch of aorta

• Right subclavian
• Right common carotid
• left subclavian
• left common caortid

I had already talked about the two system which supplies the CNS do you remember them ? :- Vertebrobasilar system and internal carotid system now let us understand how does these system actually start from these 4 major vessel

Now you need to learn that Subclavian system give a very important branch of artery named "Vertebral artery" which forms the vertebrobasilar system (do you remember that these were the vessel that actually passes from the foramen transversorium of cervical vertebrae) and you might be knowing that the common carotid artery divides into internal carotid artery and an external carotid artery it is actually the "Internal carotid artery" which contribute to the blood supply of CNS (Forgot the external carotid it has nothing to do with the blood supply of CNS)

NOTE:- One important thing that i want you to notice is that there are 2 vertebral artery , one is left vertebral artery that takes origin from the left subclavian artery ; Another is right vertebral artery which takes origin from the right subclavian artery

Similar to vertebral artery there are two internal carotid arteries , one is right internal carotid artery which takes origin from the right common carotid artey which take origin from the Brachiocephalic trunk and another one is left internal carotid artery which takes origin from the left common carotid artery.

See the diagram below:-

Let's do a Quick fast recap :-

Two system supplies the CNS - Vertebrobasilar system and Internal carotid system

• Vertebrobasilar system origin :- Arch of aorta --> Brachiocephalic trunk --> Right Subclavian --> Right Vertebral artery ..... ;
• For Left vertebral artery - Arch of aorta --> Left subclavian --> left vertebral artery
• Internal carotid system Origin :- Arch of aorta --> Brachiocephalic trunk --> Right Common Carotid --> Right internal carotid .....;
• For Left internal carotid - Arch of aorta --> Left common Carotid --> left internal carotid

Now as we had learnt about the origin of these two system from the heart , Now let's track their path toward the brain , At first we will talk about the Vertebrobasilar system

Now as vertebral has taken its origin from the subclavian artery it moves through the foramen transversorium of cervical vertebrae and at the 1st cervical vertebrae these artery moves forward and medially towards the Foramen Magnum (I HOPE YOU KNOW THAT !) and enter into that .

Now before going further let's revise what actually comes out of the foramen magnum and what lies on the clivus (if you are not aware of clivus please visit here )? do you remember?

let me revise you that pons and medulla actually sits on the clivus and spinal cord continued from brain stem come out of the foramen magnunm and Vertebral artery make entry in the foramen magnum after turning fronto-medially after coming out from foramen transversorium of 1st cervical vertebrae BUT WAIT!! we are missing something ...... we actually missed the meninges Vertebral artery cannot enter in cranial cavity until it pierces the meninges . RIGHT!

So now the Question is does the Vertebral Artery pierce all the meninges and then enter into cranial cavity Let me tell you

Actually vertebral artery pierces the duramater and arachnoid mater but it does not pierce the Piamater and it lies in the "Sub-Arachnoid space " Yes!! and you know what else is present in the Sub-Arachnoid space - It is CSF ! so it means that Vertebral artery is actually floating in the CSF (Remember the Choroid plexus , the choroid vessel also do not pierce the Piamater and it itself lies with in the CSF )

so i hope that you are clear now where actually the vessel which supply the brain is present .

Lets Quickly recap what we learnt so far:-

Brain is actually supplied by Two System :-

• Posterior Section is actually supplied by the vertebrobasilar system.
• Anterior part is actually supplied by the Carotid system.

• Vertebrobasilar system origin :- Arch of aorta --> Brachiocephalic trunk --> Right Subclavian --> Right Vertebral artery ..... ;
• For Left vertebral artery - Arch of aorta --> Left subclavian --> left vertebral artery
• Internal carotid system Origin :- Arch of aorta --> Brachiocephalic trunk --> Right Common Carotid --> Right internal carotid .....;
• For Left internal carotid - Arch of aorta --> Left common Carotid --> left internal carotid

Vertebral arteries after taking origin run via foramen transversorium to reach the top.

Vertebral artery make entry in the foramen magnum after turning fronto-medially after coming out from foramen transversorium of 1st cervical vertebrae

vertebral artery pierces the duramater and arachnoid mater but it does not pierce the Piamater and it lies in the "Sub-Arachnoid space with CSF

Vertebral artery in subarachnoid space ascends up to the level of ponto-medullary junction and then right and left vertebral artery fuse together to give rise to "BASILAR ARTERY"

I am sure that you have learnt that the basilar artery runs on the anterior side of pons , it is lodged in the median groove so that is how fusion of two vertebral artery forms the basilar artery -- now you can think about the name of this system "Vertebrobasilar System" (it comes from vertebral artery and basilar artery)

Now wait for a second---

Vertebral artery before fusing and forming basilar artery give some important branches let's first learn about them

Two small spinal artery arises from vertebral artery one from right and other from left Vertebral artery and these small spinal artery fuse to form "Anterior spinal artery" which descends down and lie on the anterior side of spinal cord and supply to anterior 2/3rd of spinal cord

OK! so anterior 2/3rd of spinal cord is supplied by anterior spinal artery so what actually supplies the posterior 1/3rd of spinal cord ?

It is posterior spinal artery , let me tell you that there are 2 posterior spinal artery and one anterior spinal artery and 2 posterior spinal artery arise directly from vertebral artery , Right posterior spinal artery arise from right vertebral artery, left posterior spinal artery arise from left vertebral artery

Long story short :- Vertebral artery before getting fused and forming basilar artery and entering in subarachnoid space give small spinal arteries , 2 anteriorly located spinal arteries fuse together to form a large Anterior Spinal artery and the the 2 posteriorly located spinal artery continue as such to form posterior spinal artery

so whole picture now look like this:-

NOTE:- Posterior spinal artery may arise directly from vertebral artery or they may arise from Posterior inferior cerebellar artery (we will talk about this later remember it as name as of now)

Now let's try to focus on the blood supply of spinal cord :-

so we had already got an idea abut blood supply of spinal cord - Anterior 2/3rd of spinal cord is actually perfused mainly by anterior spinal artery and posterior 1/3 rd of spinal cord is perfused by posterior spinal artery but the spinal cord is quite big as compared to these arteries and they are not enough to meet the need of spinal cord

So to get desired blood flow Spinal Cord recieve several reinforcement arteries which support and provide extra required blood flow to spinal cord along with the anterior and posterior spinal arteries

These reinforcement arteries are what we call as "Segmental arteries" what are they ?

Segmental arteries are arteries which arise from surrounding artery like deep cervical artery , intercoastal artery , lumbar arteries and come toward spinal cord and lie close to spinal nerve and divied into radicular branches

There arise two radicular artery one anterior radicular artery and one posterior radicular artery and go to their respective position

• Posterior radicular artery reinforce the blood supply on posterior side along with posterior spinal artery
• Anterior radicular artery reinforce the blood supply on anterior side along with anterior spinal artery

NOTE:- Now Anterior spinal artery is actually supplying anterior 2/3rd part of spinal cord and posterior spinal artery only supplies 1/3rd part of spinal cord , that is not fair , Anterior spinal artery is facing a lot of load , so to relieve that one more important artery specially supply the anterior 2/3rd of spinal cord and the artery is "ARTERY OF ADAMKIEWICZ" and this artery directly arises from the aorta (YEAH ! DIRECTLY FROM AORTA!!)

A quick fast recap :-

• Anterior 2/3rd of spinal cord is actually perfused by - 1 Anterior spinal artery , Segmental arteries and artery of Adamkiewicz
• Posterior 1/3rd of spinal cord is actually perfused by - 2 posterior spinal artery and segmental arteries

Now let's talk about an another artery which also takes origin from the Vertebral artery and it's name is Posterior inferior cerebellar artery in short called "PICA"

So basically upto now the 2 vertebral artery before merging together and forming Basilar artery gives 2 anterior spinal branches which merge to form "Anterior spinal artery " and 2 posterior spinal branches which continue as 2 posterior spinal artery and also gives 2 PICA .

Now which areas are supplied by these PICA? let's find out

PICA=posterior inferior cerebellar artery as it name shows it supplies posterior part of inferior cerebellum "note again" - Posterior part of Inferior cerebellum not superior portion of cerebellum and even not the anterior part of inferior cerebellum.

see this image to understand it more clearly:-

as you can see from above image PICA is supplying posterior part of inferior cerebellum but what you can not observe is that it also supplies the "Medulla"

YEH! so called Vomit centre is actually supplied by PICA .

Forgot not that Posterior spinal artery may arise from the PICA

Now let stick to cerebellum PICA is supplying posterior part of inferior cerebellum but what about its anterior part ?? i mean anterior part of inferior cerebellum and what's about superior cerebellum ??

So long story short anterior part of inferior cerebellum is actually supplied by another artery called "AICA" (anterior inferior cerebellar artery) which itself arises form the basilar artery. let me remind you that the basilar artery is actually present in basilar groove seen in anterior aspect of pons

see the below diagram for clear understanding:-

Now in the given image relevant things that you need to notice is that AICA arises from the basilar artery and it supplies to anterior portion of inferior cerebellum

Now about the superior cerebellum , the superior cerebellum is actually supplied by the superior cerebellar artery which also arises from "Basilar artery " and supplies the superior cerebellum

see the image below for clear understanding :-

Quick recap

• Vertebral artery gives PICA - which supplies posterior part of inferior cerebellum
• Basilar artery gives AICA- which supplies anterior part of inferior cerebellum
• Basilar artery also gives superior cerebellar artery which supplies superior aspect of cerebellum

so now whole picture look like this :-

now there is an another important artery which takes origin from the basilar artery that is Labyrinthine artery which are 2 in no. , these arteries takes origin from the basilar artery and extend and goes upto the labyrinth (internal ear) and supplies there so basically it enters in internal ear via Internal acoustic meatus

Have your ever heared or read that the 8th cranial nerve is accompained with labyrinthine vessels , now you know why ;)

WAIT A SECOND - In some people Labyrinthine artery arises from Basilar artery while in some it arises from the "AICA" , in majority it arises from AICA.

now there are also present small pontine arteries which arises from the basilar artery and perfuse the pons see the image below to have a clear idea:-

and last but not the least the basilar artery get terminated by forming two major branches :- posterior cerebral artery and these 2 posterior cerebral artery supplies the posterior part of the cerebral hemisphere

Actually these 2 posterior cerebral artery also supplies the midbrain because they go to posterior cereberum by following the sides of midbrain

see the below diagram for a more clear understanding :-

here ends the posterior supply system of brain .

let's do a quick fast recap :-

2 Vertebral artery arises from subclavian arteries and passes via Forman Transversarium to reach at the top and they converge medially and forward to reach to foamen magnum they pierce the duramater , arachnoidmater and lie in CSF

they converge to form basilar artery at the lower level of pons and this basilar artery terminates as two posterior cerebral artery.

Blood supply of components of CNS:-

Spinal Cord by -ANTERIOR 2/3rd by - Anterior spinal artery which takes origin from the vertebral artery , Artery of Adamkiewicz , anterior radicular artery

Posterior 1/3rd by - 2 posterior spinal artery which takes origin from the vertebral artery or by PICA and by Posterior radicular artery

Cerebellum by - PICA - supplies posterior part of inferior cerebellum which arises form vertebral artery

AICA - supplies anterior part of inferior cerebellum which arises from basilar artery

Superior cerebellar artery - supplies superior part of cerebellum which arises from the basilar artery .

Medulla- Supplied by PICA

Pons- Supplied by Pontine artery which arises from basilar artery

Mid Brain supplied by posterior cerebral artery

We know that testing what you have learned is always a good idea to train your brain so let me take your test Find out the answer of the given question bank below :-

Answers:-

mde

Now we are left with the anterior supply system of brain , I assure that i will be uploading it very soon . i am working very hard to provide a rich content to you (it takes a lot of effort from my side reading the topic from big elaborative books and then framing it to present in a simpler way) , if you liked the article hit like button that boost my confidence and do follow the blog and at last keep learning

Signing off

------Bhavesh saini