Blood Supply of the Brain

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6 Blood Supply of the Brain

The central nervous system is tremendously active metabolically—relative to its weight, it uses much more than its share of the available oxygen and glucose. Corresponding to this metabolic activity, it has an abundant and closely regulated arterial supply and a large venous drainage system. Also, the CNS depends for its proper functioning on carefully controlled extracellular ion concentrations. Part of the basis for this control is a system of diffusion barriers, of which cerebral blood vessels are a major part.

The Internal Carotid Arteries and Vertebral Arteries Supply the Brain

Two interconnected arterial systems provide the blood supply to the brain (Fig. 6-1). The internal carotid system of each side supplies the ipsilateral cerebral hemisphere, except for the medial surface of the occipital lobe and the medial and inferior surfaces of the temporal lobe. The vertebral-basilar system supplies those parts of the occipital and temporal lobes, as well as the brainstem and cerebellum. The supply of the diencephalon is shared by the two systems, with the vertebral/basilar system supplying most of the thalamus and the internal carotid system supplying most of the hypothalamus.

Figure 6-1 Overview of the CNS arterial supply.

The Internal Carotid Arteries Supply Most of the Cerebrum

Key Concept

Small perforating arteries supply deep cerebral structures.

The internal carotid has two major terminal branches, the anterior and middle cerebral arteries. These are two of the three arteries that supply the cerebral cortex. On their way to their cortical areas of supply, both give rise to lots of small perforating or ganglionic arteries that supply most of the hypothalamus, basal ganglia, and internal capsule. (A comparable set from the vertebral-basilar system supplies the thalamus and brainstem.) The anterior and middle cerebral arteries have large terminal areas of distribution that are suggested to some extent by the name of each artery (Fig. 6-2).

Figure 6-2 Arterial supply of the cerebral cortex. ACA, MCA, and PCA indicate areas supplied by the anterior, middle, and posterior cerebral arteries.

(Modified from Mettler FA: Neuroanatomy, ed 2. St. Louis, Mosby, 1948.)

The Vertebral-Basilar System Supplies the Brainstem and Parts of the Cerebrum and Spinal Cord

The two vertebral arteries fuse near the pontomedullary junction to form the single basilar artery, which ascends to the midbrain and terminates by bifurcating into the two posterior cerebral arteries. As they move along the brainstem, the vertebral and basilar arteries give off a series of branches; each has a name suggesting its terminal area of distribution (e.g., the superior cerebellar artery supplies the superior surface of the cerebellum). Along the way, each of these arteries provides perforating branches that supply the part of the brainstem it passes over. So knowing the levels at which these vertebral-basilar branches emerge (Fig. 6-3) provides a first approximation of the supply of the brainstem.

Figure 6-3 Vertebral-basilar and internal carotid branches. ACA, Anterior cerebral artery; ACoA, anterior communicating artery; AICA, anterior inferior cerebellar artery; BA, basilar artery; Di, diencephalon; ICA, internal carotid artery; PCA, posterior cerebral artery; PCoA, posterior communicating artery; PICA, posterior inferior cerebellar artery; SCA, superior cerebellar artery; VA, vertebral artery.