Study topic · about 4 minutes
Blood supply of the brain
Four arteries carry blood up the neck to the brain: two internal carotid arteries in front and two vertebral arteries at the back. At the base of the brain they join in a ring, the circle of Willis, which gives off three pairs of cerebral arteries: the anterior, middle and posterior cerebral arteries. Each one feeds its own territory, so a stroke in each causes its own signs.
Key points
- The brain is about 2 percent of the body's weight, but uses about a fifth of its oxygen.
- The middle cerebral artery feeds most of the outer surface: the face and arm areas and, on the left, language.
- The anterior cerebral artery feeds the inner surface of the frontal and parietal lobes, including the leg area.
- The posterior cerebral artery feeds the occipital lobe (vision), the underside of the temporal lobe and the thalamus.
- The vertebral and basilar arteries feed the brainstem and cerebellum.
The arteries that feed the brain
The two internal carotid arteries run up the front of the neck and enter the skull; they supply most of the cerebrum. The two vertebral arteries climb through the bones of the neck, enter at the back of the skull and join into a single basilar artery along the front of the brainstem. These are called the anterior (carotid) and posterior (vertebrobasilar) circulations.
The circle of Willis
At the base of the brain, the arteries link into a ring called the circle of Willis. Small communicating arteries join the front and back circulations, so if one artery narrows slowly, blood can sometimes arrive another way. In many people the ring is incomplete, and it cannot protect against a sudden blockage.
From the ring come three pairs of cerebral arteries: the anterior cerebral arteries (ACA) and middle cerebral arteries (MCA), branches of the carotids, and the posterior cerebral arteries (PCA), branches of the basilar artery.
What each artery supplies
| Artery | Supplies | A stroke here can cause |
|---|---|---|
| Anterior cerebral (ACA) | The inner surface of the frontal and parietal lobes, including the leg area of the motor and sensory strips. | Weakness and numbness of the opposite leg, more than the arm; loss of drive and trouble starting actions. |
| Middle cerebral (MCA) | Most of the outer surface, including the face and arm areas of the motor strip and, on the left, the language areas (Broca's and Wernicke's). Its deep branches feed the putamen and nearby pathways. | Weakness and numbness of the opposite face and arm; on the left, aphasia (trouble speaking or understanding); on the right, neglect of the left side of space. |
| Posterior cerebral (PCA) | The occipital lobe, the underside of the temporal lobe, and the thalamus. | Loss of the opposite half of the visual field; sometimes memory problems or pain from the thalamus. |
| Vertebral and basilar | The brainstem and the cerebellum. | Dizziness, double vision, trouble swallowing or speaking, clumsiness, and weakness or numbness that can affect both sides. A blocked basilar artery can be fatal or cause locked-in syndrome. |
Territories differ from person to person, and the borders on the 3D map are approximate.
Turn on the blood supply map in 3D
What is a stroke?
A stroke happens when blood stops reaching part of the brain. Most strokes are ischemic: a clot blocks an artery. A hemorrhagic stroke is a bleed from a burst blood vessel. Without blood, brain cells start to die within minutes, which is why fast treatment matters: medicines that dissolve the clot, and procedures that pull it out, work best in the first hours.
A transient ischemic attack (TIA), sometimes called a mini-stroke, causes the same signs but they go away within minutes to hours. It is a warning that a bigger stroke may follow.
Spot a stroke: BE FAST
- Balance: sudden loss of balance or dizziness.
- Eyes: sudden trouble seeing.
- Face: one side of the face droops when the person smiles.
- Arms: one arm drifts down when both are raised.
- Speech: slurred or strange speech.
- Time: call emergency services right away (911 in the US).
This page is for learning only. If you think someone is having a stroke, call emergency services immediately.
Why does a stroke affect the opposite side?
The main movement and touch pathways cross the midline, mostly in the lower medulla oblongata and the spinal cord, so each side of the brain controls the opposite side of the body. A stroke in the left motor cortex weakens the right side. And because language sits in the left hemisphere in most people, trouble speaking usually points to a left-sided stroke.
Quick quiz
5 questions. Your answers are saved and come back in your daily review.
A stroke weakens a patient's right face and arm and makes it hard to speak. Which artery is most likely blocked?
Show the answer
Left middle cerebral artery. The left MCA feeds the face and arm areas of the left motor strip, which control the right side, and the language areas.
Left middle cerebral artery. The left MCA feeds the face and arm areas of the left motor strip, which control the right side, and the language areas.
Which artery supplies the leg area of the motor strip?
Show the answer
Anterior cerebral artery. The leg area is on the inner surface, in the paracentral lobule, fed by the ACA.
Anterior cerebral artery. The leg area is on the inner surface, in the paracentral lobule, fed by the ACA.
A blocked posterior cerebral artery most often causes...
Show the answer
Loss of half of the visual field. The PCA feeds the primary visual cortex in the occipital lobe.
Loss of half of the visual field. The PCA feeds the primary visual cortex in the occipital lobe.
What does the "T" in BE FAST stand for?
Show the answer
Time to call emergency services. Every minute counts: treatment works best in the first hours.
Time to call emergency services. Every minute counts: treatment works best in the first hours.
Which arteries supply the brainstem and cerebellum?
Show the answer
Vertebral and basilar arteries. The posterior (vertebrobasilar) circulation feeds the brainstem and cerebellum.
Vertebral and basilar arteries. The posterior (vertebrobasilar) circulation feeds the brainstem and cerebellum.
These parts now come back in your daily review, just before you would forget them.
Practice these parts in 3DIn these study guides
- Anatomy and physiologyVentricles, fluid and blood supply (section 13.3)
- NursingStroke
- Medical schoolVascular territories and stroke syndromes
Sources
- Anatomy and Physiology 2e, 13.3 Circulation and the Central Nervous System, OpenStax
- Signs and Symptoms of Stroke, Centers for Disease Control and Prevention (CDC)
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