Blood supply to the brainCircle of Willis

Blood supply to the brain. Circle of WillisArteries and veins of the brain. Circle of Willis
~ 8 min

In this note, we are going to discuss the blood supply to the brain and its venous drainage.

Arterial supply

The arterial blood supply to the brain can be divided into the anterior and posterior circulation.

The anterior (or carotid) circulation is formed by two internal carotid arteries and their branches,

Internal carotid artery
Internal carotid artery
Internal carotid artery
Internal carotid artery

and the posterior (or vertebrobasilar) circulation is formed by two vertebral arteries and their branches.

Vertebral artery
Vertebral artery
Vertebral artery
Vertebral artery

Anterior (carotid) circulation

Let’s start from the anterior circulation. The internal carotid arteries branch off from the common carotid arteries,

Common carotid artery
Common carotid artery

enter the skull, make a series of curves, various bends, pass within the cavernous sinus,

Internal carotid artery passing in the cavernous sinus
Internal carotid artery passing in the cavernous sinus

and then on the basal surface of the brain, each of them is divided into two very important arteries we are interested in.

These are the anterior cerebral artery

Anterior cerebral artery
Anterior cerebral artery
Anterior cerebral artery
Anterior cerebral artery

and a direct continuation of the internal carotid – the middle cerebral artery.

Middle cerebral artery
Middle cerebral artery
Middle cerebral artery
Middle cerebral artery

In addition to this, the left and right anterior cerebral arteries are connected by the anterior communicating artery.

Anterior communicating artery
Anterior communicating artery
Anterior communicating artery
Anterior communicating artery

Distal to the cavernous sinus, each ICA gives rise to a couple of branches: the ophthalmic artery

Ophthalmic artery
Ophthalmic artery

and the anterior choroidal artery.

Anterior choroidal artery
Anterior choroidal artery

Posterior (vertebrobasilar) circulation

For now, let’s leave the anterior circulation for a while and move on to the posterior one. It is formed by two vertebral arteries.

Subclavian artery
Subclavian artery

They arise from the subclavian arteries and ascend along the posterior aspect of the neck, through the transverse foramina of the cervical vertebrae.

Subclavian arteryd
Subclavian arteryd
Vertebral artery - foraminal segment
Vertebral artery - foraminal segment
Vertebral artery - extradural and intradural segments
Vertebral artery - extradural and intradural segments

Then they pass through the foramen magnum

Foramen magnum
Foramen magnum

and merge to form the basilar artery, so the posterior circulation is also called vertebrobasilar.

Basilar artery
Basilar artery
Basilar artery
Basilar artery

Also, the vertebral artery gives rise to a couple of branches: these are the posterior inferior cerebellar artery

Posterior inferior cerebellar artery
Posterior inferior cerebellar artery

and the anterior spinal artery, which supply, respectively, the cerebellum and spinal cord.

Anterior spinal artery
Anterior spinal artery

Let’s get back to the basilar artery. It ascends superiorly in the basilar sulcus of the anterior aspect of the pons and gives rise to several branches: these are the anterior inferior cerebellar artery,

Anterior inferior cerebellar artery
Anterior inferior cerebellar artery

pontine arteries,

Pontine arteries
Pontine arteries

superior cerebellar artery,

Superior cerebellar artery
Superior cerebellar artery
Superior cerebellar artery
Superior cerebellar artery

and, the most important, terminal branch: the posterior cerebral artery.

Posterior cerebral artery
Posterior cerebral artery
Posterior cerebral artery
Posterior cerebral artery

Circle of Willis

The key point is that the posterior cerebral artery and the internal carotid artery are connected by the posterior communicating artery, which means that the anterior and posterior circulation are now also connected.

Posterior communicating artery
Posterior communicating artery
Posterior communicating artery
Posterior communicating artery

As a result, due to the presence of three communicating arteries (one anterior and two posterior), the arterial circle is formed on the basal surface of the brain. It is called the Circle of Willis, and its role is to provide an “emergency” blood supply to the brain if one of the four arteries is narrowed, or “blocked” for some reason.

And here (next page) is some information about the cortical branches of the anterior cerebral artery, middle cerebral artery, and posterior cerebral artery.

Venous drainage

There are two venous systems in the brain: superficial and deep.

The superficial veins collect blood, mostly from the cerebral cortex. You can see the largest of them in the picture (next page).

And the deep veins collect blood from, respectively, deeper regions of the brain. There are two types of these veins. The first is the medullary veins, which are arranged in a wedge-shaped manner.

Medullary vein
Medullary vein

So they originate approximately 1-2 cm below the cortical gray matter and eventually drain into the second type – the subependymal veins.

Subependymal vein
Subependymal vein

The most significant vein of the deep system is the great cerebral vein of Galen,

Great cerebral vein of Galen
Great cerebral vein of Galen
Great cerebral vein of Galen
Great cerebral vein of Galen

which is formed by the union of two internal cerebral veins.

Internal cerebral veins
Internal cerebral veins

We can also mention two basal veins of Rosenthal.

Basal vein
Basal vein
Basal vein
Basal vein

Eventually, veins of both systems drain blood into the dural venous sinuses, which we have already discussed in the video about the brain meninges.

And then venous blood from the sinuses gets into the internal jugular veins.

Internal jugular vein
Internal jugular vein

In addition, let’s take a look at some other functional types of veins:

  • Bridging veins are located in the subdural space and connect the superficial veins of the brain with the dural venous sinuses, mostly with the superior sagittal sinus.
  • Emissary veins connect the dural sinuses and intracranial veins with extracranial veins, meaning, veins that pass not inside the skull, but along its external surface.
Emissary vein
Emissary vein
  • Diploic veins pass within the spongy (or cancellous) tissue, called diploë, and actually drain the venous blood from the cranial bones.
Diploic vein
Diploic vein
Golosary

Blood supply to the brainCircle of Willis

internal carotid arteries
arteriae carotides internae
vertebral arteries
arteriae vertebrales
common carotid arteries
arteriae carotides communes
cavernous sinus
sinus cavernosus
anterior cerebral artery
arteria cerebri anterior
middle cerebral artery
arteria cerebri media
anterior communicating artery
arteria communicans anterior
ophthalmic artery
arteria ophthalmica
anterior choroidal artery
arteria choroidea anterior
subclavian arteries
arteriae subclaviae
foramen magnum
foramen magnum
basilar artery
arteria basilaris
posterior inferior cerebellar artery
arteria cerebelli inferior posterior
anterior spinal artery
arteria spinalis anterior
anterior inferior cerebellar artery
arteria cerebelli inferior anterior
pontine arteries
arteriae pontis
superior cerebellar artery
arteria cerebelli superior
posterior cerebral artery
arteria cerebri posterior
posterior communicating artery
arteria communicans posterior
circle of Willis
circulus arteriosus cerebri
medullary veins
venae medullares
subependymal veins
venae subependymales
great cerebral vein of Galen
vena cerebri magna
internal cerebral veins
venae cerebri internae
basal veins of Rosenthal
venae basales
dural venous sinuses
sinus durae matris
internal jugular veins
venae jugulares internae
emissary veins
venae emissariae
diploic veins
venae diploicae
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