1. Arterial Supply
Anterior Circulation (Carotid System):

Supplied by the internal carotid arteries, which branch into:
Anterior cerebral arteries (ACA): Supply the medial and superior surfaces of the frontal and parietal lobes.
Middle cerebral arteries (MCA): Supply the lateral surfaces of the frontal, parietal, and temporal lobes.
Posterior Circulation (Vertebrobasilar System):

Supplied by the vertebral arteries, which join to form the basilar artery. These give rise to:
Posterior cerebral arteries (PCA): Supply the occipital lobe, inferior temporal lobe, and brainstem.
Other branches supply the cerebellum and brainstem (e.g., posterior inferior cerebellar artery, anterior inferior cerebellar artery).
Circle of Willis: A vital anastomotic ring at the base of the brain formed by:

Internal carotid arteries, anterior and posterior cerebral arteries.
Connected by the anterior and posterior communicating arteries.
Provides collateral circulation in case of arterial blockage.