Blood Supply of the Brain PDF

Created by Turbolearn AI Blood Supply of the Brain Our brains rely heavily on a continuous supply of well-oxygenated blood. Here's a breakdown: 10 seconds of brain ischemia: Loss of consciousness. 20 seconds: Electrical activity ceases. Few minutes: Irreversible damage usually begin...

Created by Turbolearn AI Blood Supply of the Brain Our brains rely heavily on a continuous supply of well-oxygenated blood. Here's a breakdown: 10 seconds of brain ischemia: Loss of consciousness. 20 seconds: Electrical activity ceases. Few minutes: Irreversible damage usually begins. Due to this metabolic dependence, blood vessels in the central nervous system (CNS), especially in gray matter, are arranged in a dense meshwork. Cerebral Arterial Supply The cerebral arterial supply is composed of two arterial systems: 1. Carotid System 2. Vertebro-Basilar System As shown above, the brain receives blood from a complex network of arteries, including the anterior cerebral, middle cerebral, posterior cerebral, and vertebral arteries, all interconnected to ensure consistent perfusion. Page 1  Created by Turbolearn AI Superficial cortical arteries supply the gray matter on the surface. Perforating arteries supply the subcortical nuclei. Both sets of arteries send branches to the adjacent white matter. The internal carotid arteries and the vertebral arteries are the primary sources. The internal carotid arteries provide about 80% of the blood supply. The Internal Carotid Arteries The internal carotid artery is a major paired artery on each side of the head and neck. They arise from the common carotid arteries where these bifurcate into the internal and external carotid arteries at cervical vertebral level 3 or 4. As seen above, the internal carotid artery is divided into several parts, each giving rise to critical branches that supply blood to different regions of the brain. Along its course, the internal carotid artery is divided into 4 parts: Page 2  Created by Turbolearn AI Cervical part: in the neck Petrous part: in the petrous temporal bone Cavernous part: in the cavernous sinus Cerebral part: in relation to the base of the brain The image shows the path of the internal carotid artery as it proceeds superiorly alongside the optic chiasm and bifurcates into the middle and anterior cerebral arteries. Key Arteries Branching from the Internal Carotid Page 3  Created by Turbolearn AI 1. Anterior Choroidal Artery: A long, thin artery that supplies several structures. It's clinically significant because it is frequently involved in cerebrovascular accidents. It supplies: Optic tract Choroid plexus of the inferior horn 2. Posterior Communicating Artery: Passes posteriorly, inferior to the optic tract and toward the cerebral peduncle, and joins the posterior cerebral artery (part of the vertebral artery system). 3. Anterior Cerebral Artery: Runs medially, superior to the optic nerve, and enters the longitudinal fissure. The two anterior cerebral arteries are connected by the anterior communicating artery near their entrance into the longitudinal fissure. This image shows the Circle of Willis, a circulatory anastomosis that supplies blood to the brain and surrounding structures. Distal to the anterior communicating artery, the anterior cerebral artery gives off two branches: Page 4  Created by Turbolearn AI Medial striate Recurrent artery of Heubner These supply the basal ganglia and internal capsule. Then, it continues as the pericallosal artery, which stays immediately adjacent to the corpus callosum. Near the genu of the corpus callosum, the callosomarginal artery typically branches off from the pericallosal artery and follows the cingulate. Middle Cerebral Artery The large middle cerebral artery proceeds laterally into the lateral sulcus. It divides into a number of branches that supply the insula, emerge from the lateral sulcus, and spread out to supply most of the lateral surface of the cerebral. As shown above, the middle cerebral artery is a major vessel that branches extensively to supply a large portion of the brain's lateral surface. Page 5  Created by Turbolearn AI Perforating arteries are particularly numerous in the area adjacent to the optic chiasm and in the area between the cerebral peduncles; for this reason, they are called the anterior and posterior perforated substances, respectively. Vertebro-Basilar System The diagram illustrates the interconnected network of the carotid and vertebrobasilar systems, ensuring a redundant and reliable blood supply to the brain. The two vertebral arteries (from the subclavian artery) unite to form the basilar artery. It divides at the upper border of the pons into two posterior cerebral arteries. The Vertebral-Basilar System The vertebral arteries arise from the subclavian arteries, one on each side of the body. They then enter the foramen transversarium at the level of the 6th cervical vertebrae (C6), or occasionally (in 7.5% of cases) at the level of C7. They then proceed superiorly in the transverse foramen of each cervical vertebra. Before joining the basilar artery, each vertebral artery gives rise to three branches: Page 6  Created by Turbolearn AI Posterior spinal artery Anterior spinal artery Posterior inferior cerebellar artery The posterior spinal artery runs caudally along the postero-lateral aspect of the spinal. The Basilar Artery This illustration shows the intricate network of arteries at the base of the brain, including the vertebral, basilar, and cerebellar arteries. The basilar artery proceeds rostrally and, at the level of the midbrain, bifurcates into the two posterior cerebral arteries. Before this bifurcation, it gives rise to numerous unnamed branches and two named branches: Anterior inferior cerebellar artery Superior cerebellar artery The Posterior Cerebral Artery Page 7  Created by Turbolearn AI The primary visual cortex is located in the occipital lobe, so occlusion of a posterior cerebral artery at its origin leads to visual field losses, in addition to other deficits referable to the midbrain and diencephalon. Cerebral Arterial Circle (Circle of Willis) The circle of Willis is a part of the cerebral circulation and is composed of the following arteries: Anterior cerebral artery (left and right) Anterior communicating artery Internal carotid artery (left and right) Posterior cerebral artery (left and right) Arterial Supply of Other Brain Parts Page 8  Created by Turbolearn AI Corpus striatum and internal capsule: mainly by central branches (medial and lateral striate arteries) of middle cerebral artery and to some extent by central branches of anterior cerebral artery. Thalamus: mainly by central branches of posterior Blood Supply to Cerebellum Superior cerebellar artery (SCA) from basilar artery Anterior inferior cerebellar artery (AICA) from basilar artery Posterior inferior cerebellar artery (PICA) from vertebral artery The image shows the three main arteries that supply the cerebellum: the superior cerebellar artery (SCA), the anterior inferior cerebellar artery (AICA), and the posterior inferior cerebellar artery (PICA). Blood Supply to Spinal Cord The spinal cord is supplied with blood by three arteries that run along its length, starting in the brain, and many arteries that approach it through the sides of the spinal column. The three longitudinal arteries are called the anterior spinal artery and the right and left posterior spinal arteries. These travel in the subarachnoid space and send branches into the spinal cord. They form anastomoses via the anterior and. Arterial blood supply below the cervical region comes from the radially arranged posterior and anterior radicular arteries, which run into the spinal cord alongside the dorsal and ventral nerve roots. These intercostal and lumbar radicular arteries arise from the aorta, provide major anastomoses, and supplement the blood flow to the spinal cord. Page 9  Created by Turbolearn AI The largest of the anterior radicular arteries is known as the artery of Adamkiewicz. This diagram shows the horizontal distribution of blood supply to the spinal cord, highlighting the anterior and posterior spinal arteries. Note that the central area, supplied only by the anterior spinal artery, is predominantly a motor area. Venous Drainage of Brain The veins of the brain drain into the intracranial dural venous sinuses, which eventually open into the internal jugular veins of the neck. The veins emerge from the brain, traverse the subarachnoid space, pierce the arachnoid mater and meningeal layer of dura mater to drain into venous sinuses. Characteristic features: 1. Venous return in the brain does not follow the arterial pattern. 2. Divided into external and internal cerebral veins, which drain the external surfaces and the internal regions of the cerebral hemisphere, respectively. External (superficial) cerebral veins: drain the surface of the hemisphere and are divided into three groups: Page 10  Created by Turbolearn AI Superior Middle Inferior This image illustrates the superficial cerebral veins and their drainage into the superior sagittal sinus. Other Veins Page 11  Created by Turbolearn AI Anterior cerebral vein: accompanies the anterior cerebral artery around the corpus callosum and drains the parts of the medial surface which cannot be drained into the superior and inferior sagittal sinuses. Basal vein (of Rosenthal): formed at the base of the brain in the region of the anterior perforated substance by the union of three veins: Anterior cerebral Deep middle cerebral Striate veins The striate veins emerge from the anterior perforated substance. The basal vein runs posteriorly around the midbrain, medial to the uncus and. Internal Cerebral Veins Page 12  Created by Turbolearn AI There are two internal cerebral veins, located one on either side of the midline in the tela choroidea of the third ventricle. Each internal cerebral vein is formed at the interventricular foramen (of Monro) by the union of three veins: Thalamostriate Septal Choroidal The two internal cerebral veins run posteriorly. Clinical Anatomy Imaging techniques allow arteries and veins to be visualized. Blood vessels can be visualized with most imaging techniques by finding a way to make the blood contained within them differ in some way from surrounding structures. Cerebral Angiography Page 13  Created by Turbolearn AI Cerebral angiography is a radiological technique to visualize the vessels of the brain. A radiopaque solution is injected into one of the major arteries supplying the brain, and serial radiographs of the skull are taken at approximately 1-second intervals. Injections into the common carotid artery or the internal carotid artery (carotid angiogram) show the distribution of middle and anterior cerebral arteries, whereas injections into the vertebral artery. Thrombosis of lateral striate branches of the middle cerebral artery causes motor and sensory loss to most of the opposite side of the body, except the lower limb. Hemiplegia is a common condition. It is an upper motor neuron type of paralysis of one-half of the body, including the face. It is usually due to an internal capsule lesion caused by thrombosis of one of the lenticulostriate branches of the middle cerebral artery (cerebral thrombosis). Thrombosis of Heubner’s recurrent branch of the anterior cerebral artery causes contralateral upper monoplegia. Thrombosis of the paracentral artery (terminal cortical branch of the anterior cerebral artery) causes contralateral lower limb monoplegia. Arterial Disorders Stroke (Sudden occlusion of the blood supply): Hemorrhagic Ischemic Aneurysm Occlusion of Anterior Cerebral Artery (Distal to Anterior Communicating Artery) Page 14  Created by Turbolearn AI The image shows the effects of occlusion of the anterior cerebral artery, including weakness and cortical sensory loss in the contralateral lower limb. Contralateral hemiparesis and hemianaesthesia involving mainly the leg and foot, due to involvement of upper parts of primary motor and sensory areas, and paracentral lobule. Inability to identify objects correctly, due to involvement of the superior parietal lobule. Apathy and personality changes, due to involvement of part of the frontal lobe. Page 15  Created by Turbolearn AI This image shows the vascular territories of the anterior, middle, and posterior cerebral arteries, providing a clear view of the areas affected by occlusions in each artery. Occlusion of Middle Cerebral Artery Contralateral hemiparesis and hemianaesthesia involving mainly the face and arm, due to involvement of most of the Primary Motor and Sensory Areas Occlusion of the posterior cerebral artery can lead to several conditions: Aphasia: If the left dominant hemisphere is involved. Contralateral homonymous hemianopia: Due to involvement of the visual cortex, but with some degree of macular sparing. Macular vision is spared because it is represented in the occipital pole. Page 16  Created by Turbolearn AI Here's a detailed illustration of the cerebral vascular territories, showcasing two brain diagrams with distinct color-coded sections: The image includes a lateral and superior view of the brain, with yellow representing the anterior cerebral artery, red denoting the middle cerebral artery, and blue indicating the posterior cerebral artery. This helps visualize the brain's blood supply distribution. STROKES Strokes result from disruption of the vascular supply. Cerebrovascular disease and accidents are the most common causes of neurological deficits. Normally, about 55 ml of blood flows through each 100 g of CNS per minute. Any significant reduction of this perfusion rate rapidly causes malfunction or even death of neurons. Here is a CT scan of a human brain, showcasing a cross-sectional view: Page 17  Created by Turbolearn AI The grayscale image shows a large, irregularly shaped white area that dominates the right side of the brain, indicating a significant abnormality, likely a hemorrhage or lesion. Subarachnoid Hemorrhage Results from leakage or rupture of a congenital aneurysm on the circle of Willis Symptoms include sudden, severe headache, stiffness of the neck, and loss of consciousness Aneurysms Aneurysms (Greek for ‘dilation’) are balloon-like swellings of arterial walls. They occur most frequently at or near arterial branch points. Those close to the brain usually occur in or near the anterior half of the cerebral arterial circle, although they are also found at other locations. An aneurysm can cause... Here is a microscopic view of a neuron, a type of nerve cell: Page 18  Created by Turbolearn AI The neuron has a distinctive teardrop-shaped cell body, also known as the soma, from which a long, thin extension called an axon emerges. Page 19