including the occipital lobes, cerebellum and brainstem. It is supplied by the following arteries: Vertebral arteries: These smaller arteries branch from the subclavian arteries which primarily supply the shoulders, lateral chest, and arms. Within the cranium the two vertebral arteries fuse into the basilar artery. Posterior inferior cerebellar artery (PICA) Basilar artery: Supplies the midbrain, cerebellum, and usually branches into the posterior cerebral artery Anterior inferior cerebellar artery (AICA) Pontine branches Superior cerebellar artery (SCA) Posterior cerebral artery (PCA) Posterior communicating artery Venous drainage The venous drainage of the cerebrum can be separated into two subdivisions: superficial and deep. The superficial system The superficial system is composed of dural venous sinuses, sinuses (channels) within the dura mater. The dural sinuses are therefore located on the surface of the cerebrum. The most prominent of these sinuses is the superior sagittal sinus which is located in the sagittal plane under the midline of the cerebral vault, posteriorly and inferiorly to the confluence of sinuses, where the superficial drainage joins with the sinus that primarily drains the deep venous system. From here, two transverse sinuses bifurcate and travel laterally and inferiorly in an S-shaped curve that forms the sigmoid sinuses which go on to form the two jugular veins. In the neck, the jugular veins parallel the upward course of the carotid arteries and drain blood into the superior vena cava. The veins puncture the relevant dural sinus, piercing the arachnoid and dura mater as bridging veins that drain their contents into the sinus. The deep venous system The deep venous system is primarily composed of traditional veins inside the deep structures of the brain, which join behind the midbrain to form the great cerebral vein (vein of Galen). This vein merges with the inferior sagittal sinus to form the straight sinus which then joins the superficial venous system mentioned above at the confluence of sinuses. Physiology Cerebral blood flow (CBF) is the blood supply to the brain in a given period of time. In an adult, CBF is typically 750 millilitres per minute or 15% of the cardiac output. This equates to an average perfusion of 50 to 54 millilitres of blood per 100 grams of brain tissue per minute. CBF is tightly regulated to meet the brain's metabolic demands. Too much blood (a clinical condition of a normal homeostatic response of hyperemia) can raise intracranial pressure (ICP), which can compress and