BLOOD SUPPLY OF BRAIN (Basic Anatomy and Physiology)

Hi, myself Dr. Sayan Pratihar (MPT-Neurology), am sharing the ppt on the concept of Basic Anatomy and Physiology of human brain's blood supply. I hope you all find this content useful. Thank you.

1. BLOOD SUPPLY OF BRAIN SAYAN PRATIHAR MPT (NEUROLOGY)

2. ARTERIES OF BRAIN Two vertebral and two internal carotid arteries carry the total arterial supply to the brain. VERTEBRAL ARTERY BASILAR ARTERY INTERNAL CAROTID ARTERY

3. Cerebral circulation Cerebral circulation  is the movement of  blood  through a network of  cerebral arteries  and  veins  supplying the  brain . The rate of cerebral  blood flow  in an adult  human  is typically 750  milliliters  per  minute , or about 15% of  cardiac output . ( Muoio et al. 2014; Acta Physiologica.210[4]:790-8) The  neurovascular unit  regulates cerebral blood flow so that activated neurons can be supplied with energy in the right amount and at the right time.  The cerebral circulatory system has safeguards including  autoregulation  of the  blood vessels . The failure of these safeguards may result in a  stroke .  The  volume  of blood in circulation is called the  cerebral blood flow .

4. (ANATOMY) BLOOD SUPPLY Blood supply to the brain is normally divided into anterior and posterior segments, relating to the different arteries that supply the brain. The two main pairs of arteries are the  Internal carotid arteries  (supply the anterior brain) and  vertebral arteries  (supplying the  brainstem  and posterior brain). The anterior and posterior cerebral circulations are interconnected via bilateral  posterior communicating arteries . In case one of the supply arteries is occluded, the Circle of Willis provides interconnections between the anterior and the posterior cerebral circulation.

5. Anterior cerebral circulation The  anterior cerebral circulation  is the blood supply to the anterior portion of the brain including  eyes . It is supplied by the following arteries: Internal carotid arteries : These large arteries are the medial branches of the  common carotid arteries  which enter the skull, as opposed to the  external carotid  branches which supply the facial tissues; the internal carotid artery branches into the  anterior cerebral artery  and continues to form the  middle cerebral artery .

6. BRANCHES: Anterior cerebral artery  (ACA): The  anterior cerebral artery  ( ACA ) is one of a pair of  cerebral arteries  that supplies oxygenated blood to most midline portions of the  frontal lobes  and  superior medial parietal   lobes of the brain . The two anterior cerebral arteries arise from the  internal carotid artery  and are part of the  circle of Willis .  Deep branches of anterior cerebral artery supply part of internal capsule and the basal nuclei. Cortical branches supply the medial surface of hemisphere by giving: a. Orbital b. Frontal c. Parietal

7. Middle Cerebral Artery  (MCA): The  middle cerebral artery  ( MCA ) is one of the three major paired  cerebral arteries  that supply  blood  to the  cerebrum . The MCA arises from the  internal carotid artery  and continues into the  lateral sulcus  where it then branches and projects to many parts of the lateral  cerebral cortex . It also supplies blood to the anterior  temporal lobes  . It ends by giving cortical branches to: Temporal lobe b. Frontal lobe c. Parietal lobe.

8. Posterior communicating artery: It passes posteriorly across the crus cerebri to join the posterior cerebral artery and helps to complete the arterial circle. It gives branches to the crus cerebri /cerebral penduncles , optic tract, hypophysis (pituitary gland) and hypothalamus. Anterior choroidal artery: It passes posterolaterally , supplies crus cerebri and turns laterally to the medial aspect of temporal lobe to supply choroid plexus of inferior horn of lateral ventricle.

9. Outer surface of cerebral hemisphere, showing areas supplied by cerebral arteries. Areas supplied by the anterior cerebral artery are shown in blue.

10. Posterior cerebral circulation The  posterior cerebral circulation  is the blood supply to the posterior portion of the brain, 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 .

11. (BRANCHES) Posterior Inferior Cerebellar Artery(PICA): It is the largest branch which arises from vertebral artery. It supplies almost lateral half of medulla as far as the lower border of pons , reaches its posterior aspect between the thin roof of cavity of fourth ventricle and cerebellum, gives a choroidal branch to the choroid plexus of fourth ventricle and turns downwards on the cerebellum supplying it. Medullary Branches: As vertebral artery ascends along medulla oblongata, it gives number of branches to the medulla oblongata.

12. BASILAR ARTERY It Supplies the  midbrain ,  cerebellum , and usually branches into the  posterior cerebral artery . Anterior inferior cerebellar artery : It arises at the lower border of pons , and passes laterally, supplying the sixth, seventh and eighth cranial nerves. It then loops over the flocculus of cerebellum and supplies anteroinferior aspect of cerebellum. Pontine branches: These are numerous slender branches which pierce the pons both in the medial and lateral parts. Superior cerebellar artery: It arises close to superior border of pons . It winds posteriorly along the superior border of pons and middle cerebellar peduncle, supplying both. It sends many branches to the superior surface of cerebellum.

13. The posterior cerebral artery (PCA) : It is one of a pair of  cerebral arteries  that supply oxygenated  blood  to the  occipital lobe . The two  arteries  originate from the distal end of the  basilar artery , where it bifurcates into the left and right posterior cerebral arteries. These anastomose with the  middle cerebral arteries  and  internal carotid arteries  via the  posterior communicating arteries . BRANCHES: Posteromedial central branches : These supply midbrain and caudal part of diencephalon. Posterior choroidal artery : Arises on the lateral aspect of central branches, supplies choroid plexus of the lateral ventricle and the third ventricle. Cortical branches: namely temporal branches, parieto occipital branch and occipital branch to cerebral cortex.

14. Posterior communicating artery: Anteriorly , it unites with the  internal carotid artery  (ICA) (prior to the terminal bifurcation of the ICA into the  anterior cerebral artery  and  middle cerebral artery ); posteriorly , it unites with the  posterior cerebral artery . With the  anterior communicating artery , the posterior communicating arteries establish a system of  collateral circulation  in  cerebral circulation .

15. BLOOD SUPPLY OF THE BRAINSTEM The midbrain is supplied by branches from the posterior cerebral arteries, including their central branches, both posteromedial and posterolateral . The pons is supplied by the pontine branches of basilar artery. The medulla is supplied by: a. The medullary branches of the vertebral artery. b. Branches from the posterior inferior cerebellar artery. The veins of the brainstem drain into neighbouring venous sinuses.

16. Important arteries of brain ARTERY ORIGIN COURSE CORTICAL BRANCHES Middle Cerebral Largest and direct branch of ICA In the lateral sulcus and on the insula Orbital Frontal 3. Parietal 4. Temporal Anterior Cerebral Smaller terminal branch of ICA Coextensive with corpus callosum . Two arteries are connected by the anterior communicating artery Orbital Frontal Parietal, including paracentral artery Posterior Cerebral Terminal branch of basilar artery Winds round cerebral peduncle to reach the tentorial surface of cerebrum 1. Temporal 2. Occipital 3. Parieto -occipital

17. ARTERIAL SUPPLY OF DIFFERENT AREAS Cerebral Cortex Middle cerebral is main artery on superolateral surface. Anterior cerebral artery is chief artery on medial surface. Posterior cerebral is principal artery on inferior surface. Cerebellum The little brain is supplied by following arteries: Superior cerebellar Anterior inferior cerebellar Posterior inferior cerebellar

18. CIRCULUS ARTERIOSUS OR CIRCLE OF WILLIS It is a hexagonal arterial circle, situated at the base of brain in the inter peduncular fossa . It is formed by the anterior cerebral branches and terminal parts of internal carotid arteries with its posterior communicating branch and the posterior cerebral branches of basilar artery. Branches The branches are cortical, central and choroidal . Cortical or external branches run on the surface of the cerebrum, anastomose freely and if these get blocked, they give rise to small infarcts. The central branches perforate the white matter to supply the thalamus, the corpus striatum, and the internal capsule. These do not anastomose and if these get blocked, they give rise to large infarcts. Choroidal branches supply the choroid plexuses of the various ventricles.

19. CLINICAL ANATOMY Thrombosis of posterior cerebral artery results in homonymous hemianopia (loss of visual field) on the same side. Thrombosis of superior cerebellar artery results in : a. Cerebellum: Disturbed gait, limb ataxia. b. Brainstem: Ipsilateral Horner’s syndrome. (syndrome of eye and surrounding tissues on one side of face). Contra lateral sensory loss—pain and temperature (including face). Damage to anterior inferior cerebellar artery results in a. Cerebellum: Ipsilateral limb ataxia. b. Brainstem: Ipsilateral Horner’s syndrome .( Oculosympathetic Palsy) Sensory loss—pain and temperature of face. Facial weakness and paralysis of lateral gaze. Contralateral sensory loss—pain and temperature of limbs and trunk. Thrombosis of posterior inferior cerebellar artery causes damage as given in (Fig. 11.8): a. Cerebellum: Dysarthria , ipsilateral limb ataxia, vertigo and nystagmus (due to damage to vestibulofloccular connections). b. Brainstem: Ipsilateral Horner’s syndrome. Sensory loss—pain and temperature of face. Pharyngeal and laryngeal paralysis. Contralateral sensory loss—pain and temperature of limbs and trunk.

20. CLINICAL ANATOMY Thrombosis of lateral striate branches of middle cerebral artery causes motor and sensory loss to most of the opposite side of body except 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 middle cerebral artery (cerebral thrombosis). Thrombosis of Heubner’s recurrent branch of the anterior cerebral artery causes contralateral upper limb monoplegia . Thrombosis of the paracentral artery (terminal cortical branch of the anterior cerebral artery) causes contralateral lower limb monoplegia .

21. BLOOD–BRAIN BARRIER The  blood–brain barrier  ( BBB ) is a highly selective  semipermeable  border of  endothelial cells  that regulates the transfer of solutes and chemicals between the  circulatory system  and the  central nervous system , thus protecting the  brain  from harmful or unwanted substances in the  blood .  The blood– brain  barrier is formed by endothelial cells of the  capillary wall . This system allows the passage of some small molecules by  passive diffusion , as well as the selective and active transport of various nutrients, ions, organic anions, and macromolecules such as glucose and  amino acids  that are crucial to neural function.

22. VEINS OF THE BRAIN External Cerebral Veins Superior cerebral veins Superficial middle cerebral vein Deep middle cerebral vein Inferior cerebral veins Anterior cerebral veins Internal Cerebral Veins Terminal Veins Basal vein Great cerebral vein of Galen

23. Physiology  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. Too much blood can raise  intracranial pressure  (ICP), which can compress and damage delicate brain tissue. Too little blood flow ( ischemia ) results if blood flow to the brain is below 18 to 20 ml per 100 g of brain tissue per minute, and tissue death occurs if flow dips below 8 to 10 ml per 100 g per minute.

24. Cerebral blood flow is determined by a number of factors, such as  viscosity  of blood, how dilated  blood vessels  are, and the net pressure of the flow of blood into the brain, known as  cerebral perfusion pressure , which is determined by the body's  blood pressure . Cerebral perfusion pressure (CPP) is defined as the mean arterial pressure (MAP) minus the intracranial pressure (ICP). [MAP-ICP= Cerebral Perfusion Pressure]. In normal individuals, it should be above 50 mm Hg. Intracranial pressure should not be above 15 mm Hg (ICP of 20 mm Hg is considered as intracranial hypertension). 

25. Cerebral blood vessels are able to change the flow of blood through them by altering their diameters in a process called  cerebral autoregulation ; they constrict when systemic blood pressure is raised and dilate when it is lowered. Arterioles also constrict and dilate in response to different chemical concentrations. For example, they dilate in response to higher levels of  carbon dioxide  in the blood and constrict in response to lower levels of carbon dioxide.

26. References 1.  Muoio , V; Persson , PB; Sendeski , MM (April 2014).  "The neurovascular unit - concept review" .  Acta Physiologica .  210  (4): 790-8.  doi : 10.1111/apha.12250 .  PMID   24629161 .  S2CID   25274791 . 2.   Cipolla , Marilyn J. (2009).  "Anatomy and Ultrastructure " . National Center for Biotechnology Information, U.S. National Library of Medicine. Morgan & Claypool Life Sciences. Retrieved June 22, 2021. 3.   Chandra, Ankush ; Li, William A; Stone, Christopher R; Geng , Xiaokun ; Ding, Yuchuan (2017-07-17).  "The cerebral circulation and cerebrovascular disease I: Anatomy" . Brain Circulation.  3  (2): 45-56   doi : 10.4103/bc.bc_10_17 .  PMC   6126264 .  PMID   30276305 . 4.“Carotid Arterial System" . The Lecturio Medical Concept Library. Retrieved 2021-06-22. 5. Wikipedia 6.Gray’s anatomy 7.Neuroanatomy Volume 4; B.D. Chaurasia

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