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Circle of Willis Quiz

Twenty questions on the arteries at the base of the brain, from naming them to matching strokes and aneurysms. The diagram shows the brain from below, front at the top. Tap an answer to see if you’re right.

  1. Question 1 of 20

    Name the highlighted single artery in the middle, formed where two others join.

    Arteries at the base of the brain, seen from below (front at the top)
    1. Anterior spinal artery
    2. Middle cerebral artery
    3. Basilar artery
    4. Internal carotid artery
    Show answer

    Answer: Basilar artery. The two vertebral arteries join to make the basilar artery, which runs up the front of the brainstem.

  2. Question 2 of 20

    Name the highlighted big arteries entering at the sides of the circle.

    Arteries at the base of the brain, seen from below (front at the top)
    1. External carotid arteries
    2. Middle cerebral arteries
    3. Vertebral arteries
    4. Internal carotid arteries
    Show answer

    Answer: Internal carotid arteries. The carotids bring most of the brain’s blood, about 80%. The vertebrals bring the rest.

  3. Question 3 of 20

    Name the highlighted arteries running out to the sides of the brain.

    Arteries at the base of the brain, seen from below (front at the top)
    1. Posterior cerebral arteries
    2. Middle cerebral arteries
    3. Anterior cerebral arteries
    4. Superior cerebellar arteries
    Show answer

    Answer: Middle cerebral arteries. The biggest branches of the carotids, running in the groove between the frontal and temporal lobes.

  4. Question 4 of 20

    Name the highlighted arteries running forwards between the hemispheres.

    Arteries at the base of the brain, seen from below (front at the top)
    1. Anterior cerebral arteries
    2. Middle cerebral arteries
    3. Ophthalmic arteries
    4. Anterior communicating artery
    Show answer

    Answer: Anterior cerebral arteries. They curve up and back along the inner surface of each hemisphere.

  5. Question 5 of 20

    Name the highlighted arteries at the back end of the circle.

    Arteries at the base of the brain, seen from below (front at the top)
    1. Posterior communicating arteries
    2. Superior cerebellar arteries
    3. Vertebral arteries
    4. Posterior cerebral arteries
    Show answer

    Answer: Posterior cerebral arteries. The basilar artery ends by splitting into the two posterior cerebral arteries, which feed the occipital lobes.

  6. Question 6 of 20

    Name the highlighted pair of arteries that join to make the basilar.

    Arteries at the base of the brain, seen from below (front at the top)
    1. Anterior spinal arteries
    2. Posterior cerebral arteries
    3. Vertebral arteries
    4. Internal carotid arteries
    Show answer

    Answer: Vertebral arteries. They run up through holes in the neck vertebrae, which is why neck injuries can tear them.

  7. Question 7 of 20

    Name the short highlighted artery joining the two front arteries.

    Arteries at the base of the brain, seen from below (front at the top)
    1. Anterior communicating artery
    2. Basilar artery
    3. Ophthalmic artery
    4. Posterior communicating artery
    Show answer

    Answer: Anterior communicating artery. It links left and right anterior cerebral arteries, completing the front of the circle.

  8. Question 8 of 20

    Name the highlighted arteries linking front and back circulations.

    Arteries at the base of the brain, seen from below (front at the top)
    1. Middle cerebral arteries
    2. Posterior communicating arteries
    3. Superior cerebellar arteries
    4. Anterior communicating artery
    Show answer

    Answer: Posterior communicating arteries. They join each internal carotid to the posterior cerebral artery on the same side.

  9. Question 9 of 20

    Name the highlighted arteries leaving the top of the basilar, just below the posterior cerebrals.

    Arteries at the base of the brain, seen from below (front at the top)
    1. Anterior inferior cerebellar arteries
    2. Superior cerebellar arteries
    3. Posterior cerebral arteries
    4. Posterior inferior cerebellar arteries
    Show answer

    Answer: Superior cerebellar arteries. They wrap round the brainstem to the top of the cerebellum. Cranial nerve III runs between them and the posterior cerebrals.

  10. Question 10 of 20

    Name the highlighted arteries leaving the vertebral arteries.

    Arteries at the base of the brain, seen from below (front at the top)
    1. Anterior inferior cerebellar arteries
    2. Superior cerebellar arteries
    3. Posterior inferior cerebellar arteries (PICA)
    4. Anterior spinal arteries
    Show answer

    Answer: Posterior inferior cerebellar arteries (PICA). PICA is the largest branch of each vertebral artery, feeding the lower cerebellum and side of the medulla.

  11. Question 11 of 20

    Name the highlighted arteries leaving the lower basilar.

    Arteries at the base of the brain, seen from below (front at the top)
    1. Pontine arteries
    2. Superior cerebellar arteries
    3. Posterior inferior cerebellar arteries
    4. Anterior inferior cerebellar arteries (AICA)
    Show answer

    Answer: Anterior inferior cerebellar arteries (AICA). AICA feeds the front of the lower cerebellum and part of the pons, and usually gives the artery to the inner ear.

  12. Question 12 of 20

    What is the main benefit of having a circle?

    1. Backup flow if one artery narrows
    2. It filters clots
    3. It cools the brain
    4. It makes cerebrospinal fluid
    Show answer

    Answer: Backup flow if one artery narrows. If one carotid slowly narrows, blood can detour round the circle. Only about half of people have a complete circle, though.

  13. Question 13 of 20

    Weakness of the face and arm (leg mostly spared) and trouble finding words suggest a stroke in which highlighted artery?

    Arteries at the base of the brain, seen from below (front at the top)
    1. Left middle cerebral artery
    2. Right posterior cerebral artery
    3. Basilar artery
    4. Left anterior cerebral artery
    Show answer

    Answer: Left middle cerebral artery. The MCA feeds the side of the brain, where face and arm are mapped, plus the language areas in the dominant (usually left) hemisphere.

  14. Question 14 of 20

    Leg weakness much worse than arm weakness suggests a stroke in which highlighted artery?

    Arteries at the base of the brain, seen from below (front at the top)
    1. Middle cerebral artery
    2. Anterior cerebral artery
    3. Posterior cerebral artery
    4. Vertebral artery
    Show answer

    Answer: Anterior cerebral artery. The leg is mapped on the inner surface of the hemisphere, which the ACA supplies.

  15. Question 15 of 20

    Losing the same half of the visual field in both eyes, with no weakness, suggests a stroke in which highlighted artery?

    Arteries at the base of the brain, seen from below (front at the top)
    1. Anterior cerebral artery
    2. Middle cerebral artery
    3. Ophthalmic artery
    4. Posterior cerebral artery
    Show answer

    Answer: Posterior cerebral artery. The PCA feeds the occipital (visual) cortex. Central vision is often spared because the MCA helps supply that spot.

  16. Question 16 of 20

    Vertigo, hoarseness, a droopy eyelid, and numbness of one side of the face and the other side of the body suggest blockage of which highlighted artery?

    Arteries at the base of the brain, seen from below (front at the top)
    1. AICA
    2. Middle cerebral artery
    3. PICA
    4. Anterior cerebral artery
    Show answer

    Answer: PICA. Lateral medullary (Wallenberg) syndrome, often from the vertebral artery or PICA. Crossed signs point to the brainstem.

  17. Question 17 of 20

    Blockage of the highlighted artery can leave someone fully aware but able to move only their eyes. What is this?

    Arteries at the base of the brain, seen from below (front at the top)
    1. Locked-in syndrome
    2. Akinetic mutism
    3. Brain death
    4. Persistent vegetative state
    Show answer

    Answer: Locked-in syndrome. A basilar artery blockage can destroy the front of the pons, cutting all movement but sparing consciousness and up-and-down eye movements.

  18. Question 18 of 20

    Where in the circle do brain (berry) aneurysms most often form?

    Arteries at the base of the brain, seen from below (front at the top)
    1. Vertebral artery
    2. Anterior communicating artery
    3. Basilar tip
    4. Superior cerebellar artery
    Show answer

    Answer: Anterior communicating artery. Aneurysms favour branch points at the front of the circle. Acom is the commonest site, then the posterior communicating and middle cerebral.

  19. Question 19 of 20

    A new painful droopy eyelid with a large pupil suggests an aneurysm of which highlighted artery pressing on nerve III?

    Arteries at the base of the brain, seen from below (front at the top)
    1. Middle cerebral artery
    2. PICA
    3. Posterior communicating artery
    4. Anterior communicating artery
    Show answer

    Answer: Posterior communicating artery. The pupil fibres run on the outside of nerve III, so outside pressure blows the pupil early. Emergency scan.

  20. Question 20 of 20

    Sudden vertigo with deafness in one ear and facial weakness on the same side suggests a stroke in which highlighted artery?

    Arteries at the base of the brain, seen from below (front at the top)
    1. Posterior cerebral artery
    2. Superior cerebellar artery
    3. PICA
    4. AICA
    Show answer

    Answer: AICA. AICA usually gives off the labyrinthine artery to the inner ear, so sudden one-sided deafness is the clue that separates it from PICA.

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Common questions

What arteries make up the circle of Willis?

The two anterior cerebral arteries joined by the anterior communicating artery at the front, the two internal carotids, the two posterior communicating arteries, and the two posterior cerebral arteries at the back, which come off the basilar artery.

What does the circle of Willis do?

It joins the front (carotid) and back (vertebral and basilar) blood supplies, so blood can detour if one artery is slowly narrowed. Many people don’t have a complete circle.

Where do brain aneurysms form?

Mostly at branch points at the front of the circle: the anterior communicating artery, the posterior communicating artery where it meets the internal carotid, and the middle cerebral artery.

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Updated 16 November 2026. Diagrams are simplified, original sketches, not to scale. General education, not personal medical advice.