Human Anatomy: Part 2 - K. A. Dyubenko, A. K. Kolomiytsev, Yu. B. Chaykovsky 2008

Special Part
Nervous system, systema nervosum — Special Part
Meninges of the brain — Blood supply to the brain

The Blood supply to the Brain is provided simultaneously by four main Arteries—the paired internal carotid and vertebral arteries, which are interconnected at the Base of the brain by extensive anastomotic links (the cerebral arterial circle), as well as by superficial and deep Veins through which venous blood drains into the Dural Venous Sinuses of the brain.

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Fig. 171. Diagram illustrating the sources of CEREBROSPINAL FLUID production, sites of its absorption, and return to the Venous system (according to J. P. Schade and D. H. Ford, 1976). The arrows indicate the direction of cerebrospinal fluid (CSF) flow, with the size of the arrow corresponding to the flow intensity.

Fig. 172 A. Cerebral arteries on a sagittal section (viewed from the Medial surface of the hemisphere)

Fig. 172 B. Cerebral arteries (viewed from the Superolateral surface of the hemisphere)

Cerebral arteries are muscular-type vessels with extensive adrenergic and cholinergic innervation; therefore, by significantly altering their lumen, they can participate in The regulation of cerebral blood supply.

The Internal Carotid Artery, a. carotis interna, is the largest (paired) blood vessel supplying the anterior Regions of the brain. It branches into the anterior cerebral artery, a. cerebri anterior, the middle cerebral artery, a. cerebri media, the choroidal artery, a. chorioidea, and the posterior communicating artery, a. communicans posterior (Figs. 27, 172 A). The right and left anterior cerebral arteries anastomose with each other via a short anterior communicating artery, a. communicans anterior, which is highly variable in diameter.

The vertebral arteries, aa. vertebrales, merge at the base of the Brainstem to form the Basilar artery, a. basilaris, which then divides into two posterior cerebral arteries, aa. cerebri posterior (Figs. 27, 172 B). Each posterior cerebral artery anastomoses with the internal carotid artery via the posterior communicating artery, a. communicans posterior.

Thus, an arterial circle is formed in the subarachnoid space at the base of the brain (the arterial nonagon described by M. A. Tikhomirov in 1880), also known as the cerebral arterial (Willisian) circle, circulus arteriosus cerebri. The Functions of the circle of Willis include dampening pulse waves, ensuring a uniform blood supply, and providing the primary line of collateral anastomoses between inflow vessels. In the absence of the anterior cerebral artery or one of the posterior communicating arteries, the circle remains incomplete. Various anatomical Variants of the circle of Willis are observed (V. Adaschi, B. K. Hyndtze, B. D. Bekov, S. S. Mikhailov) (Fig. 173), (M. I. Shamayev, T. A. Malysheva, 2005) (Fig. 174).

Fig. 173 A. Variants of the arterial circle at the base of the brain according to D. B. Bekov: 1 - embryonic form of the arterial circle (significant Development of the posterior communicating artery); 2 - transitional form; 3 - differentiated form (poor development of the posterior communicating artery)

Fig. 173 B. Variants of the arterial circle at the base of the brain according to B. K. Hyndtze

1 - incomplete arterial circle (complete type); 2 - symmetric arterial circle; 3 - incomplete arterial circle (partial type)

* In 1664, Willis described an arterial heptagon, but it did not account for the sides formed by the a. carotis interna.

The cerebral hemispheres are supplied with blood by the paired anterior, middle, and posterior cerebral arteries, whose trunks and branches are located On the surface of the brain within the subarachnoid space. The arterial trunks and branches form wide anastomoses with one another, thereby ensuring collateral blood supply to the brain. Thanks to this anastomotic system, a uniform blood pressure is maintained in the arteries on the brain's surface. The anterior cerebral arteries supply the medial surface of the hemispheres up to the parieto-occipital sulcus, and on the lateral surface—the superior frontal gyrus and the superior margin of the parietal lobe; on the Inferior surface of the hemispheres, they supply the gyrus rectus of the frontal lobe (basomedian branches). The middle cerebral arteries supply the insula, the two central gyri, the inferior frontal gyrus, the greater part of the middle frontal gyrus, the parietal lobe, as well as the superior and middle temporal gyri. The posterior cerebral arteries supply the medial, inferior, and lateral surfaces of the temporal and occipital lobes, with the exception of the superior and middle temporal gyri.

These arteries give rise to cortical branches and White matter branches (medullary arteries), as well as central (basal) branches originating from the base of the brain (from the cerebral and choroidal arteries). They anastomose with each other to form an intraorgan vascular network. Cortical arteries supply the Cerebral Cortex, while medullary arteries supply the white matter. Cortical arteries are subdivided into short ones, with a diameter of 15-20 µm, and long ones, 40-45 µm. Short branches ramify within cortical layers 2-3, whereas long branches reach layers 5-6, supplying not only the lower two-thirds of the cortex but also the white matter. The basal nuclei (caudate Nucleus, globus pallidus, putamen, and the adjacent part of the internal capsule) are supplied by striate branches, rami striati, which arise from the anterior and middle cerebral arteries, as well as the anterior choroidal artery. The number and size of branches from the anterior cerebral artery vary and can reach up to eight. The primary source of blood supply to the basal nuclei is the middle cerebral artery, a. cerebri media, which gives off the striate branches, rr. striati. All basal nuclei are permeated by capillaries; the capillary distribution in the striatum resembles that of the cerebral cortex. The blood supply to the choroid plexuses of the brain ventricles is provided by the anterior choroidal artery, a. choroidea anterior (a branch of the internal carotid artery) and the posterior choroidal branches, rr. choroidei posteriores (Branches of the posterior cerebral artery).

A characteristic feature of cerebral blood supply is that arteries do not penetrate the brain tissue at a single point (there is no portal system), but rather spread across The surface of the brain and give off numerous branches. This feature ensures a uniform distribution of blood flow across the brain's surface, creates optimal conditions for cortical Nutrition, and establishes a system of arterial anastomoses (R. A. Pfeifer, V. P. Kurkovsky, B. V. Ognev, B. N. Klosovsky, et al.).

The blood supply to the Cerebellum is provided by three paired cerebellar arteries (the superior cerebellar artery, the anterior inferior cerebellar artery, and the posterior inferior cerebellar artery) and, occasionally, an unpaired median artery (the inferior median cerebellar artery). The superior cerebellar artery, a. cerebelli superior, is a branch of the basilar artery (occasionally the posterior cerebral artery). Before reaching the cerebellum, this artery supplies the cerebral peduncle, the superior colliculi, and the Oculomotor nerve nuclei. The anterior inferior cerebellar artery, a. cerebelli inferior anterior (a branch of the basilar artery), supplies the posterior and lateral PARTS OF THE Pons, as well as the roots of Cranial Nerves VI, VII, and VIII. The posterior inferior cerebellar artery, a. cerebelli inferior posterior, may arise from the vertebral or basilar artery, subsequently dividing into two, three, or sometimes four branches that supply the roots of cranial nerves IX and X, the posterolateral parts of the Medulla Oblongata, the anteroinferior surface of the pons, and the choroid plexus of the Fourth ventricle. On the cerebellar surface, the arteries anastomose with one another, forming an extensive network of anastomoses that gives rise to short penetrating vessels (cortical) for the cerebellar cortex (Fig. 175) and penetrating vessels (medullary) directed toward the white matter and cerebellar nuclei (Fig. 175). One or two arterioles penetrate each folium of the cerebellum, dividing into 10-15 precapillary arterioles. The latter reach the molecular layer and branch in a T-shaped manner, forming recurrent branches that supply the cortical layers and the WHITE MATTER OF the cerebellar folium (K. Dyubenko, 1973) (Fig. 176).

Fig. 174. Variants of the arterial circle at the base of the brain (according to M. I. Shamayev and T. A. Malysheva)

1 - left-sided posterior and right-sided anterior trifurcation; 2 - right-sided anterior trifurcation (combined with the middle cerebral artery); 3 - duplication of the anterior communicating artery; 4 - left-sided anterior and right-sided posterior trifurcations (combined with the middle cerebral artery and anterior cerebral artery); 5 - incomplete arterial circle (left-sided anterior trifurcation) (combined with the middle cerebral artery and anterior cerebral artery); 6 - incomplete arterial circle (absence of the left posterior communicating artery) (combined with the middle cerebral artery of the right side)

The blood supply to the medulla oblongata is provided by the anterior spinal artery, a. spinalis anterior, as well as branches of the vertebral arteries, the basilar artery, and the inferior cerebellar artery (see p. 30, "Zakharchenko's arterial ring").

Fig. 175. Angioarchitecture of the human cerebellar cortex. Cortical vessels. Injection with India ink suspension FMN-2.05.10. (Prepared by K. Dubenko)

Fig. 175 A. Blood supply to the dentate Nucleus of the human cerebellum (medullary vessels). Vascular injection (India ink + gelatin), Nissl staining. (Prepared by K. Dubenko)

Fig. 176. Angioarchitecture of a cerebellar cortical gyrus in humans (after K. Dubenko). Injection (India ink + gelatin). FMN-2.05.10.

Venous drainage from the brain is carried out into the superficial and deep veins, as well as into the dural venous sinuses. Blood from the cerebral hemispheres flows into the superficial veins, whereas blood from the choroid plexuses, lateral and third ventricles, and most of the basal nuclei drains into the great cerebral vein (v. cerebri magna). From the medial surface of the hemispheres, blood flows into the superior sagittal sinus, while from the thalamus and remaining subcortical nuclei it drains into the thalamostriate veins (vv. thalamostriati). These veins unite with the VEINS OF THE septum pellucidum, hippocampus, subependymal white matter bounding the ventricles, and the veins of the choroid plexuses to form the internal cerebral veins, which empty into the v. cerebri magna, which in turn drains into the straight sinus. The basal veins, which drain blood from the basal regions of the corpus striatum, Hypothalamus, and Midbrain, also empty into this vein. Compression of these veins during pathological brain conditions leads to secondary hemorrhages into the brainstem (M. I. Shamayev, 1983).

Venous drainage from the cerebellum is performed by cerebellar veins, which are highly variable, with their number ranging from 6 to 22. They anastomose extensively with one another and channel blood into the dural venous sinuses (sinus rectus, sinus transversus, sinus sigmoideus, sinus petrosus inferior).