Blood Vessels

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How does blood reach the brain?

The brain receives blood via four major arteries:

• two carotid arteries (arteriae carotides) at the front of the neck
• two vertebral arteries (arteriae vertebrales) at the back

The carotid arteries primarily supply blood to the anterior and middle parts of the brain.

The vertebral arteries converge into the basilar artery. Together with their branches they supply blood to the brainstem, the cerebellum, and the posterior part of the brain, among other areas.

The arteries are colored red in the image below.

Blood supply to:

The two carotid arteries (arteriae carotis) and their branches

The common carotid artery (Arteria carotis communis arises from the aortic arch or a major branch of this arch (truncus brachiocephalis).

This carotid artery branches at the level of the angle of the jaw into:

• Inner carotid artery / Arteria carotis interna,
• Outer carotid artery / Arteria carotis externa

By BruceBlaus. When using this image in external sources it can be cited as:Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010.
ISSN 2002-4436. - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=30634275

External carotid artery

The external carotid artery supplies blood to, among others:

• the thyroid gland
  
• the larynx
  
• the tongue
  
• the face and facial muscles

Internal carotid artery

The internal carotid artery (arteria carotis interna) runs through the neck to the skull. Inside the skull, it gives off an artery to the eye, among others, and then branches further to the brain.

Anterior cerebral artery (ACA)

The anterior cerebral artery (arteria cerebri anterior) primarily supplies blood to parts on the inside of the frontal lobe
and the parietal lobe.

Middle cerebral artery (MCA)

The middle cerebral artery (arteria cerebri media) supplies blood to a large part of the outer surface of the brain, including parts of:

• frontal lobe
  
• temporal lobe
  
• parietal lobe
  
• insula (isle of Reil)

Smaller branches run deeper into the brain and supply blood to various brain regions there.

Anterior choroidal artery

The anterior choroidal artery (arteria choroidea anterior) is a small artery that supplies blood to various deeper brain regions, including parts of:

• capsula interna
  
• globus pallidus
  
• hippocampus
  
• amygdala
  
• lateral geniculate body
  
• choroid plexus

Posterior communication artery (PCom)

The posterior communication artery (arteria communicans posterior) forms a connection between the blood vessels at the front and back of the brain. This artery is part of the Circle of Willis.

Small branches supply blood to parts of the hypothalamus, the thalamus, and the area around the third ventricle, among others.

The connection may sometimes help to divert blood to a part of the brain via an alternative route.

The two vertebral arteries (arteriae vertebralis) and their branches: the vertebrobassilar system

The two vertebral arteries (arteriae vertebrales) originate from the left and right subclavian arteries (arteria subclavia).

The left and right vertebral arteries run upwards to the brain. At the transition from the medulla oblongata to the pons, they merge and form the basilar artery (arteria basilaris).
The basilar artery and its branches primarily supply the blood to the pons and contribute to the blood supply to the cerebellum and other parts of the posterior cerebral circulation.

BruceBlaus. Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. - Own work

The main arteries of the posterior cerebral circulation (the vertebrobasilar system)

The main arteries of the vertebrobasilar system are

• Arteria spinalis anterior (ASA) anterior spinal artery 
• Arteriae spinalis posterior (ASP) posterior spinal arteries
• Arteria cerebelli posterior inferior (PICA) posterior inferior cerebellar artery
• Arteria cerebelli anterior inferior (AICA) anterior inferior cerebellar artery
• Arteria cerebelli superior (SCA) superior cerebral artery

The PICA usually originates from the vertebral artery.

Occlusion of the PICA or a nearby part of the vertebral artery may lead to lateral medullary syndrome, also known as Wallenberg syndrome.

The AICA and SCA are branches of the basilar artery.

Posterior cerebral artery (PCA)

At the upper end, the basilar artery splits into the left and right posterior cerebral arteries (arteria cerebri posterior, PCA).

The PCA and its branches supply blood to parts of the following areas, among others:

• the occipital lobe
• the bottom and inside of the temporal lobe
• the thalamus
• other deeper brain regions

The occipital lobe plays an important role in processing what we see. An infarct in the territory of the PCA can therefore cause vision problems, for example, loss of part of the visual field.

The posterior communicating artery (arteria communicans posterior, PCom) connects the posterior cerebral artery to the internal carotid artery and forms part of the Circle of Willis (see below).

Circle of Willis

The Circle of Willis (ring of Willis) is a network of arteries at the base of the brain. This vascular ring connects the blood supply to the left and right sides and to the front and back of the brain.
Due to these connections, blood can flow to a part of the brain via an alternative route in certain situations when blood flow via an artery is reduced. How well this is possible varies from person to person. The structure of the Circle of Willis exhibits many normal anatomical variations.

The main arteries that form the Circle of Willis are:

• anterior cerebral arteries (arteriae cerebri anteriores, ACA)
  
• anterior communicating artery (arteria communicans anterior, ACom)
  
• internal carotid arteries (arteriae carotides internae, ICA)
  
• posterior communicating arteries (arteriae communicantes posteriores, PCom)
  
• posterior cerebral arteries (arteriae cerebri posteriores, PCA)

More information about the circle of Willis is on this wikipedia page.

                    Forehead

            Back of the head

Image credits: Rhcastilhos - File:Gray519.png, Public domain, https://commons.wikimedia.org/w/index.php?curid=6187585

The brain seen from below

The cerebral blood vessels we are looking at in the images below lie in the confined space between the floor of the cranial cavity and the bottom of the brain.

In the image below you can see Willis' circle at the top. The names of the arteries are either on the left or on the right, but the arteries can be seen on both sides. Arteria is abbreviated to Art. The top images show the same view, but with the brain drawn from below.

It looks like a "doll" pattern with "legs". The circle of Willis is actually a hexagon of blood vessels in the base of the head.

The image on the right shows the same representation, but with the brain drawn in, viewed from below. You can recognize the pattern of a "little figure" with "legs," as it were.

The Circle of Willis is a hexagon of blood vessels at the base of the head.
Left image Dr. Johannes Sobotta [Public domain]

Brain viewed from below

Blood supply to the cerebrum

The cerebrum receives blood via three major cerebral arteries:

• anterior cerebral artery (ACA)
  
• middle cerebral artery (MCA)
  
• posterior cerebral artery (PCA)

Blood supply to the brainstem

The blood supply to the brainstem comes mainly from the vertebrobasilar vascular system, with branches from the vertebral arteries and basilar artery, among others.

Blood supply to the cerebellum

The cerebellum receives blood via three major arteries:

• SCA
  
• AICA
  
• PICA

Blood supply to the spinal cord

The spinal cord receives blood via the anterior and posterior spinal arteries (ASA and PSA), among others.

Blood supply areas of the three major cerebral arteries

The colors in the image show which parts of the cerebral cortex are primarily supplied with blood by the three major cerebral arteries.

Yellow: anterior cerebral artery (arteria cerebri anterior, ACA)

Red: middle cerebral artery (arteria cerebri media, MCA)

Blue: posterior cerebral artery (arteria cerebri posterior, PCA)

The brain regions that supply these blood vessels with blood:

Author unknown. According to Google pictures there is no specific author of this diagram/ could not be definitively identified based on the available information. The image appears to be widely
shared, potentially originating from a source like "The Radiologist - CVS vascular territories" on Facebook.

The veins of the brain: the venous system

The veins of the brain drain oxygen-poor blood and metabolic products from the brain tissue.

A distinction is made between a superficial and a deep venous system.

Superficial and deep cerebral veins

The superficial cerebral veins drain blood primarily from the cerebral cortex and the more superficially located parts of the brain. The deep cerebral veins drain blood from deeper brain regions.

These cerebral veins ultimately drain the blood into the dural venous sinuses.

These are blood channels located between the layers of the dura mater.

Drainage via the venous sinuses

Part of the venous blood converges at the confluens sinuum. Here, among others, the superior sagittal sinus, the straight sinus, and the occipital sinus meet. From the confluens sinuum, the blood flows further via the transverse sinuses and subsequently the sigmoid sinuses.

Finally, the blood leaves the skull via the internal jugular vein.

The superficial venous system is depicted below.

A video about blood supply to the brain:

In case you are aware of your complaints or your failure, you may be able to find out which blood vessel is involved and vice versa.
Download the diagram here with possible complaints in case of failure of the specific cerebral artery:

Blood circulation in the skull

The bony skull receives blood via multiple arteries, including the middle meningeal artery.

Blood flow to the scalp

The scalp receives blood from the posterior auricular artery (near the ear), occipital artery (near the back of the head) and from the superficial temporal arteries (near the temples). In addition, the scalp receives blood from the two branches of the internal carotid artery, supra-orbital and supratrochlear.

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