The brain uses about 20 percent of the body's oxygen and cannot store energy, so a few minutes without blood flow injures it. Four arteries supply it: two internal carotids in front and two vertebrals at the back.
Anterior circulation
Each internal carotid artery gives off the anterior and middle cerebral arteries, which feed most of the frontal, parietal and temporal lobes.
Posterior circulation
The two vertebral arteries join to form the basilar artery, which supplies the brainstem and cerebellum. It then splits into the posterior cerebral arteries for the occipital lobes.
Circle of Willis
Communicating arteries at the base of the brain link the front and back circulations into a ring. The ring can reroute blood when one artery narrows slowly, and it is a common site for aneurysms.
Venous drainage
Blood leaves through veins into the dural venous sinuses and then the internal jugular veins. Bridging veins that cross to the sinuses can tear in a head injury and cause a subdural hematoma.
| Artery | Supplies | Typical stroke signs |
|---|---|---|
| Anterior cerebral | Medial frontal and parietal lobes | Leg weaker than arm on the opposite side |
| Middle cerebral | Lateral surface of the hemisphere | Face and arm weaker than leg, aphasia if on the left |
| Posterior cerebral | Occipital lobe, lower temporal lobe, thalamus | Loss of half of the visual field |
| Vertebral and basilar | Brainstem and cerebellum | Dizziness, double vision, trouble swallowing, poor coordination |
At the bedside
Matching the signs to an artery helps the stroke team, but the key bedside task is to recognize the stroke, note the last known well time and get an urgent CT to rule out bleeding.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).