Which structure ensures a continuous blood supply to the brain?

• A. Arterial circle
• B. Internal carotid arteries
• C. Basilar artery
• D. Cerebral veins

Answer: (A)

The main idea here is the brain’s need for a steady blood supply and how redundancy in the cerebral circulation helps ensure it. The arterial circle, known as the Circle of Willis, is a ring of arteries at the base of the brain that connects the major inflow routes from the internal carotid arteries and the basilar artery. It links the anterior and posterior circulations through the anterior communicating artery and the posterior communicating arteries. This setup allows blood to be rerouted if one vessel narrows or occludes, so other pathways can continue delivering blood to essential brain regions. Cerebral veins, by contrast, drain blood from the brain and do not provide arterial supply. In many people the circle is complete, which supports continuous perfusion, though it can be incomplete in others, reducing this collateral safety.