Human Anatomy - M.M. Kurepina, A.P. Ozhigova, A.A. Nikitina 2010

Nervous system
Brain
Blood supply to the brain

The Brain receives arterial Blood from two sources: the internal carotid and vertebral Arteries.

At the level of the optic chiasm, the Internal Carotid Artery (a. carotis interna) divides into two terminal branches (Atl. Figs. 135-137). One of them, the middle cerebral artery (a. cerebri media), is a large vessel that runs deep into the lateral sulcus, vascularizing (supplying blood to) most of the cerebral hemisphere. It courses along the lateral sulcus, and its branches supply blood to the insula, the precentral and postcentral, inferior and middle frontal, parietal, and superior and middle temporal gyri. The other branch, the anterior cerebral artery (a. cerebri anterior), runs backward along the corpus callosum, supplying the gyri on the Medial surface of the hemisphere. The anterior cerebral arteries of both sides are connected near their origin by the short anterior communicating artery (a. communicans anterior). Each internal carotid artery is connected by the posterior communicating artery (a. communicans posterior) to the posterior cerebral artery (a. cerebri posterior) (a branch of the vertebral artery) on its respective side. As a result, an "arterial circle" ("Circle of Willis") is formed around the Pituitary Gland.

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Fig. 3.54. Development of the Cerebral Cortex in a child (after Shevchenko):

A — 4.5 months; B — 1 year 3 months; C — 3 years 2 months.

The vertebral arteries (a. vertebralis) enter the Skull through the foramen magnum and merge at the posterior border of the Pons to form the single Basilar artery (a. basilaris) (see Atl. Fig. 135A). Running along the ventral surface of the pons, it gives off branches that supply the pons and the Cerebellum. At the anterior border of the pons, the basilar artery divides into two posterior cerebral arteries (a. cerebri posterior), which supply the posterior part of the hemispheres. Numerous thin central arteries arise from the arterial circle and the three cerebral arteries, penetrating deep into the brain tissue. Short arteries supply the upper three layers of the cortex, while long (medullary) arteries supply its deeper layers. After passing through the cortex, the latter enter the White matter. The highest percentage of hemorrhages is associated with pathological Changes in the walls of the central cerebral arteries.

Venous drainage from the brain occurs through Veins that empty into the venous sinuses (Atl. Fig. 138). Blood from these sinuses drains via the sigmoid sinus into the Internal jugular vein (v. jugularis interna). Through inconstant openings in the cranial bones—emissary veins—blood from the venous sinuses also passes into the subcutaneous VEINS OF THE HEAD.

CEREBROSPINAL FLUID, which provides hydrostatic and barrier protection for the brain, also drains into the venous sinuses. Produced in the choroid plexuses, it bathes the walls of the brain cavities and enters the subarachnoid space through special openings in the posterior medullary velum. Its drainage occurs through the arachnoid granulations into the venous sinuses, as well as along the Lymphatic vessels in this membrane and especially in the nerve sheaths.

The intensity of BLOOD FLOW IN different PARTS OF THE brain is not constant and depends on many factors. Modern Research Methods make it possible to observe its changes in the corresponding brain regions during mental exertion, the performance of specific tasks, etc.

Table 3.1 Timeline of myelination of the main pathways in the CNS (after Badalyan)