Blood Supply of the Brain Anatomy Arteries Circle of Willis and Clinical Correlation
ANATOMY

Blood Supply of the Brain Anatomy Arteries Circle of Willis and Clinical Correlation

Jan 4, 2026 3 min read

Blood Supply of the Brain

Introduction

The brain, despite forming only about 2% of total body weight, receives nearly 20–25% of cardiac output. Continuous cerebral perfusion is essential because neurons have high metabolic demand and minimal energy storage. The blood supply of the brain is designed with dual arterial systems and collateral circulation to protect against ischemia.

Arterial Supply of the Brain

The arterial supply is divided into two major systems:

1. Internal Carotid Arterial System (Anterior Circulation)

Supplies approximately two-thirds of the cerebral hemispheres.

Origin

  • Common carotid artery → Internal carotid artery (ICA)

Major Branches of ICA

  • Anterior cerebral artery (ACA)
  • Middle cerebral artery (MCA)
  • Posterior communicating artery
  • Anterior choroidal artery

Areas Supplied

  • Frontal lobe (motor, behavior)
  • Parietal lobe (sensory)
  • Lateral temporal lobe (language)
  • Basal ganglia and internal capsule (via lenticulostriate branches)

2. Vertebrobasilar System (Posterior Circulation)

Supplies the brainstem, cerebellum, occipital lobes, and part of temporal lobes.

Origin

  • Subclavian artery → Vertebral arteries → Basilar artery

Branches

  • Posterior inferior cerebellar artery (PICA)
  • Anterior inferior cerebellar artery (AICA)
  • Superior cerebellar artery (SCA)
  • Posterior cerebral artery (PCA)

Areas Supplied

  • Brainstem (midbrain, pons, medulla)
  • Cerebellum
  • Occipital lobe (visual cortex)
  • Inferior temporal lobe

Circle of Willis

A hexagonal arterial anastomotic ring located at the base of the brain.

Components

  • Anterior cerebral arteries (right and left)
  • Anterior communicating artery
  • Internal carotid arteries
  • Posterior communicating arteries
  • Posterior cerebral arteries

Functions

  • Provides collateral circulation
  • Maintains cerebral perfusion during arterial blockage
  • Equalizes pressure between anterior and posterior circulation

Cortical Arterial Territories

Anterior Cerebral Artery (ACA)

  • Medial frontal and parietal lobes
  • Motor and sensory areas for contralateral lower limb

Middle Cerebral Artery (MCA)

  • Lateral surface of cerebral hemispheres
  • Motor and sensory cortex for face and upper limb
  • Dominant hemisphere → speech areas

Posterior Cerebral Artery (PCA)

  • Occipital lobe
  • Visual cortex
  • Inferior temporal lobe

Deep Cerebral Blood Supply

Supplied by perforating arteries:

  • Lenticulostriate arteries (from MCA)
  • Thalamoperforators (from PCA)

Structures Supplied

  • Basal ganglia
  • Internal capsule
  • Thalamus

These vessels are end arteries, highly prone to lacunar infarcts.

Venous Drainage of the Brain

Superficial Cerebral Veins

  • Drain cerebral cortex
  • Empty into dural venous sinuses

Deep Cerebral Veins

  • Internal cerebral veins
  • Great cerebral vein (vein of Galen)

Dural Venous Sinuses

  • Superior sagittal sinus
  • Inferior sagittal sinus
  • Straight sinus
  • Transverse sinus
  • Sigmoid sinus → Internal jugular vein

Regulation of Cerebral Blood Flow

  • Autoregulation maintains constant flow (MAP 60–160 mmHg)
  • Increased CO₂ → Vasodilation
  • Decreased O₂ → Vasodilation
  • Sympathetic tone has minimal effect

Clinical Correlation

Common Stroke Territories

  • MCA stroke: Contralateral hemiplegia (face > leg), aphasia
  • ACA stroke: Contralateral leg weakness, behavioral changes
  • PCA stroke: Visual field defects

Other Conditions

  • Berry aneurysm (Circle of Willis)
  • Hypertensive hemorrhage (lenticulostriate arteries)
  • Vertebrobasilar insufficiency

Key Points for Exams

  • Brain receives 750 mL/min blood flow
  • MCA is most commonly occluded artery
  • Lenticulostriate arteries are end arteries
  • Circle of Willis provides collateral circulation

⚡ Interactive MCQ Quiz

Frequently Asked Questions

The brain is supplied by two main arterial systems: the internal carotid arteries forming the anterior circulation and the vertebrobasilar system forming the posterior circulation.
The middle cerebral artery is the most commonly involved artery in ischemic stroke due to its large size and direct continuation from the internal carotid artery.
The Circle of Willis is an arterial anastomotic ring at the base of the brain that connects the internal carotid and vertebrobasilar systems and provides collateral circulation.
The anterior cerebral artery supplies the medial surfaces of the frontal and parietal lobes including the motor and sensory areas for the contralateral lower limb.
The posterior cerebral artery supplies the occipital lobe and primary visual cortex.
Lenticulostriate arteries are small penetrating branches of the middle cerebral artery that supply the basal ganglia and internal capsule and are prone to hypertensive hemorrhage and lacunar infarcts.
The vertebrobasilar system including the vertebral arteries and their branches such as PICA AICA SCA and basilar artery supplies the brainstem and cerebellum.
Cerebral autoregulation is the ability of cerebral blood vessels to maintain constant blood flow despite changes in systemic blood pressure typically between mean arterial pressures of 60 to 160 mmHg.
Berry aneurysms are caused by congenital weakness in arterial walls and most commonly occur at bifurcation points of arteries in the Circle of Willis.
Venous blood from the brain drains through superficial and deep cerebral veins into dural venous sinuses and finally into the internal jugular veins.
Related Topics
blood supply of brain cerebral circulation internal carotid artery vertebrobasilar system circle of Willis arterial supply of brain venous drainage of brain cerebral arteries brain blood flow
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