Most of the blood supply to the cerebral hemispheres comes from the internal carotid artery as well as the vertebral basilar artery system.
1. Common carotid artery system: divided into internal carotid and external carotid arteries, the internal carotid artery system is called the anterior circulation, is the main blood vessel supplying the front 3/5 of the cerebral hemisphere, and with the vertebral arteries to form a willis ring supplying the brain, so the internal carotid arteries are prone to stenosis due to the patient’s long-term hypertension, diabetes mellitus, hyperlipidemia, and other underlying diseases.
After the carotid artery stenosis, the plaque is dislodged, and it is most likely to form anterior circulation ischemia, which leads to cerebral infarction, hemianopsia, blackout, diplopia, and limb movement disorder.
2. Basilar artery system: It is called the posterior circulation. The basilar artery is formed by the confluence of the left and right vertebral arteries at the lower edge of the cerebral bridge, with the starting point generally located at the midpoint of the pontine sulcus, between the left and right spreading nerve roots, and travels upward in the basal sulcus of the cerebral bridge, with its dorsal side being the basal part of the cerebral bridge, and its ventral side being parallel to the slope and about 2 to 3 mm apart.
The total length of the basilar artery is about 3cm, and it divides into the left and right posterior cerebral arteries to the midpoint of the pontine sulcus, which is the endpoint of the basilar artery, located between the left and right motor nerve roots. So if the carotid artery is blocked, the condition is more serious if it is of acute onset.
Under normal circumstances, the direction of blood flow in the arteries that make up the ring is certain, and they do not mix with each other, and the basilar artery ring plays its role in collateral circulation only when the blood flow in the proximal end of a certain artery is blocked, and when there is a pressure difference between the arteries in the ring.