Neuroanatomy
Brain Vasculature
An illustrated guide to the blood supply of human brain
This article is mainly my notes from the course on Neuroscience and Neuroanatomy taught by Dr. Najeeb. I thought it might come in handy for those who are just looking for a starter on vasculature of the brain. The course taught by Dr. Najeeb is more than 100 hours of content and goes into the depths of neuroanatomy and also talks about some pathologies in the brain. This article assumes basic understanding of some anatomical terms and a basic understanding of the brain structurally.
I am a software engineer by profession who is just fascinated by Human Brain. So I try to learn as much as possible about it. The illustrations are just a bad effort to take notes quickly while listening to the lectures. Don’t take this article too seriously, as I said this is just a culmination of my notes from the course and could be error prone purely due to my understanding or translation errors. You can refer to the actual course for the accurate information. If you notice any errors in the following article please point out and I will be happy to learn more.
Blood Supply to the Brain
Our heart pumps about 5 litres of blood per minute at rest. Of this about 15–20% i.e. 750 ml to 1 litre goes to the brain. So lets start with the heart.
The blood supply to the brain can be divided into two distinct systems
- Carotid System
- Vertebral Basilar system
Carotid System is Anterior blood supply system and the Vertebral system is the posterior blood supply system.
The Vertebral Arteries go through the cervical vertebrae going through the Foramen Transversarium. The Vertebral Arteries go up move medially and and enter the cranium through the Formen Magnum. The left and right vertebral arteries meet and fuse together at the Pontomedullary Junction.
All these major arteries and circle of willis is present in the Sub Arachnoid space floating around in Cerebro Spinal Fluid (CSF). That is why when berry aneurysms, which are commonly present in the circle of willis, rupture result into a Sub Arachnoid Haemorrhage
The Posterior System
Lets talk about the posterior system or the Vertebral Basillar system. The Vertebral arteries as we saw move up and enter the cranium through the Foramen Magnum and combine to form Basillar artery after which they branch again into Posterior cerebral Arteries or PCA.
The vertebral arteries also branch out into Posterior Inferior Cerebellar Arteries or PICA which The PICA supplies blood to the medulla oblongata; the choroid plexus and tela choroidea of the fourth ventricle; the tonsils; the inferior vermis, and the inferior parts of the cerebellum. This is not to be confused with the Posterior Cerebral arteries which are superior to the PICA which supply blood to the occipital lobe, as well as the medial and inferior aspects of the temporal lobe.
The Basillar artery gives rise to two branches of Anterior Inferior Cerebellar Artery or AICA. In some people this branch can originate from the vertebral arteries before they get fused into the Basillar. The Basillar artery trunk has multiple branches called Pontine Arteries which supply blood to pons and adjacent parts of the brain.
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From the AICA also originates Labyrinthine Artery which supplies blood to the inner ear of our auditory system.
This is mostly the major arteries in the Vertebral Basillar system or the Posterior system. We will now talk about the Anterior system or the Carotid system
The Carotid System
The carotid system or the Anterior system as the name suggests supplies blood to the Anterior part of the brain, duh! These two systems fuse together in something called as a Circle of Willis which we had mentioned before.
Lets start with the Internal Carotid Artery or ICA. ICA starts from the Common Carotid artery which is branched from Aorta. The internal Carotid artery moves upwards and enters the Carotid Canal in the base of the cranium. Since the Carotid canal does not have an opening into the middle cranial fossa. The artery then bends and moves out of the canal through the Foramen lacerum into the middle cranial fossa into Cavernous Sinus, one of the dural venous sinuses. It pierces the Dura Mater and finally enters the Sub Arachnoid Space.
From the ICA the Opthalmic artery branches out which gives rise to the Retinal Artery which supplies blood to the retina. This is particularly important since we know that the ICA supplies blood to the retina so if a thrombi which may have come from left atrium or the mitral valve or from the aortic valve or some atherosclerotic plaque can travel into the carotid circulation and block the retinal supply causing blindness.
The ICA branches out to the Posterior Communicating Artery and the Anterior Choroidal Artery before branching into the terminal branches called Middle Cerebral Artery or MCA and Anterior Cerebral Artery or ACA. The ACA moves over the corpus collosum and supplies blood to midline portions of the frontal lobes and superior medial parietal lobes of the brain. The MCA supplies blood to many parts of the lateral cerebral cortex . It also supplies blood to the anterior temporal lobes and the insular cortices.
Circle Of Willis
The posterior communicating artery originating from the carotid is actually “communicating” to the posterior system. It connects the carotid to the Posterior Cerebral Arteries we saw earlier. Also the Right Carotid and Left Carotid also communicate with each other through the Anterior Communicating Artery not to be confused with the other ACA which is the terminal branch of Internal Carotid called Anterior Cerebral Artery. These arteries, posterior communicating artery, ICA, Anterior cerebral artery, anterior communicating artery and the Posterior cerebral artery form a circle like structure which is called the Circle of Willis
These are the major arteries of the brain which supply blood to the most important organ in our body. As I said this is just the basic structure of the major arteries in the brain vasculature. There are lot of small branches which come out of all the arteries which we have discussed in this article. We will discuss those in some other article.
Dr. Najeeb’s lectures are really useful and detailed if you want to learn about Neuroanatomy. He discusses the anatomy of the brain in great details in over 100 hours of content. This article is just a compression of 2 hours of his lectures. The course is highly recommended if you are looking to learn about neuroanatomy.
I found a lot of sites which were really helpful in helping me visualise the vasculature of the brain. Linking some of those below. Of course wikipedia is always helpful.
