Blood Supply Of Brain &

Blood Supply of Brain & Spinal Cord

Blood Supply of Spinal Cord: -receives blood supply from 3 longitudinal arteries channels that extend along length of cord. -anterior spinal arteries is present in relation to anterior median sulcus. -two posterior spinal arteries one on each side run postero lateral sulcus -in addition, piamater covering spinal cord has arteries plexus called arteria vasocorona. -main source of blood supply to spinal arteries is from vertebral arteries (from where anterior & posterior spinal arteries take origin)

-but blood from vertebral arteries reach only up to cervical segment of cord. -spinal arteries also receives blood through radicular arteries that reach cord along roots of spinal nerves -radicular arteries arise from spinal branches of vertebral, ascending cervical, deep cervical, intercostal, lumbar & sacral arteries. -one anterior radicular branches is very large & called arteria radicularis magna.

-veins of spinal cord are arranged in form of six longitudinal channels: anteromedian, posteromedian, & paired anterolateral & posterolateral -these channel are interconnected by plexus of veins that form venous vasocorona -blood from these veins is drained by radicular veins that opens into a venous plexus lying between dura & vertebral canal (epidural or internal plexus) & through it into various segmental veins.

Arterial Supply of Cerebrum: -the main arteries are internal carotid, vertebral & basilar artery. Cerebral part of internal carotid artery: -piercing duramater forms roof of cavernous sinus:-gives 3 large branches: 1) Ophthalmic artery supplies orbit. 2) Anterior cerebral artery 3) Middle cerebral artery -two smaller branches are 1) Posterior communicating artery 2) Anterior choroidal artery.

Anterior Cerebral Artery: -arises from internal carotid artery below ant. perforated substance, lateral to optic chiasm -runs medially crossing above optic nerve to longitudinal fissure of two cerebral hemisphere. -arteries of two sides lie close together & are united to each other by ant. communicating artery -artery turns to reach genu of corpus callosum -winds round front of genu & runs backwards just above body of corpus callosum -recurrent branch of anterior cerebral artery(artery of Heubner) runs laterally backwards to enter anterior perforated substances

Middle Cerebral Arteries: -runs laterally in depth of stem of lateral sulcus -curves on to superolateral surface & runs backwards in depth of posterior ramus of lateral sulcus -its cortical area supply entire lateral surface of hemisphere except leg area supplied by ACA -central branch supply lentiform & caudate nucleus

Posterior Communicating Artery: -runs backward & anastamoses with posterior cerebral artery help to complete circle of Willi’s.

Cranial Part of Vertebral a.: -gives the following branches: 1)Meningeal branches: supply bone & dura in post cranial fossa 2)Posterior spinal artery: may arise from vertebral a. or post.inferior cerebellar a.-supplies post 1/3rd of spinal cord. 3)Ant. spinal a.:supplies ant 2/3rd of spinal cord 4)Post.inf. Cerebellar artery: largest branch supplies vermis, central nuclei of cerebellum, part of cerebellar hemisphere, medulla & choroid plexus of 4th ventricle. 5)Medullary artery: small branches supplies to medulla oblangata.

Basilar Artery & its branches: -formed union of left & right vertebral arteries at lower border of pons. -ascends in midline ventral to pons & ends at its upper border by dividing right & left posterior cerebral arteries.-Branches are following : 1)Pontine artery: supplies pons 2)Labyrinthe artery: supplies internal ear. 3)Ant. inf cerebellar artery: supply ant & inf. part of cerebellum 4)Sup. Cerebellar artery: Supplies surface of cerebellum.- also gives supply to pineal gland & superior medullary velum.

Posterior Cerebral Artery: -joined by post. communicating artery branch of internal carotid artery # cortical branches: supplies inferior & medial surface of temporal lobe, lat & medial surface of occipital lobe thus supplies the visual cortex. # central branches supplies parts of thalamus, lentiform nucleus, mid brain, pineal gland & MGB # choroidal branches supplies choroid plexus of lateral ventricle & 3rd ventricle.

Arterial supply of Cerebral Hemisphere: -Anterior, middle & posterior cerebral arteries give rise to two sets of branches. 1) cortical & 2) central. Arterial supply of cerebral cortex: -is supplied by cortical branches of anterior, middle & posterior cerebral arteries -greater part of superolateral part is supplie by middle cerebral artery except strip about 2 cm wide along superomedial border extending form frontal pole to parieto occpital sulcus is supplied by ACA. The area belonging to occipital lobe is supplied by PCA. Inferior temporal gyrus is also supplier by PCA.

-main artery supplying medial surface is anterior cerebral artery(ACA) except in occipital lobe supplies PCA -in inferior surface, lateral part of orbital surface is supplied by MCA & medial part is supplied by ACA.- also tentorial surface is supplied by PCA but temporal pole is supplied by MCA. So main somatic & sensory areas is supplied by MCA except in upper most part leg which is supplied by ACA and also auditory area supplied by MCA & visual area by PCA.

Arterial supply of other parts of Cerebral Hemisphere -internal capsule is supplied by central branches of middle cerebral artery (lenticulostriate branches), anterior cerebral artery(Heubner’s recurrent branch), posterior communicating artery & anterior choroidal artery. -corpus striatum is chiefly by anterolateral central branches of middle cerebral artery & partly by anteromedial central branches from anterior cerebral & anterior communicating arteries.

-thalamus is chiefly by postero medial & posterolateral central branch of posterior cerebral artery & party by anteromedial branches.

Choroid Plexuses: -choroid plexus of lateral & third ventricles are supplied by anterior choroidal artery branch of ICA. & posterior choroidal artery branch of PCA -choroid plexus of 4th ventricle is supplied by branch from posterior inferior cerebellar artery.

Anatomical Pecularities of Cerebral Arteries: # circulus arteriosus (circle of willis) #BBB formed by structures between blood & nerve cells. Thus the BBB is made up of vessels wall, arachnoid layer, perivascular space, neuroglia & ground substance of brain.- it permits selective pasage of blood contents to nervous tissue so toxic & harmful substances are prevented from reaching brain. #central branches of cerebral arteries are end arteries so thrombosis of any of them will cause infarction.

Veins of the Cerebrum Characteristics of Veins: -walls are devoid of muscles -no valves -maintain patency some of them open into cranial sinuses against direction of blood flow in sinus. eg. Superior cerebral veins draining into superior saggital sinus.

External Cerebral Veins: -six to twelve in number-drain superolateral surface of hemisphere & terminate in superior saggital sinus. -superficial middle cerebral veindrains area round posterior ramus of lateral sulcus-terminates in cavernous sinus or sphenoparietal sinus. –through superior & inferior anastomotic veins communicates with SSS & Transverse sinus. – also communicates with deep middle cerebral veins.

Deep median cerebral vein -drains surface of insula & terminates in basal vein. Inferior cerebral veins -several in number-divided into orbital & tentorial veins.-orbital veins terminate in superior cerebral veins or in posterior saggital sinus-tentorial veins terminate in cavernous or any other surrounding sinus Anterior cerebral veins: -small veins drain into corpus callosusm & anterior part of medial surface of hemisphereterminate into basal veins.

Internal Cerebral Veins: -one vein on each side-formed by union of thalamostriate & choroidal veins at apex of tela choroidea of 3rd ventricle -right & left veins runs posteriorly parallel to each other in tela chorodea & unite together to form great cerebral vein below the splenium of corpus callosum

Terminal Veins -Great cerebral vein:- single median vein formed by union of two internal cerebral veins. – terminates into straight sinustributaries are basal veins & veins from pineal body, colliculi, cerebellum & adjoing part of occipital lobe of cerebrum -Basal veins:-one on each side- is formed by union of deep middle cerebral veins, anterior cerebral veins & striate veins- runs posteriorly winds round cerebral peduncle & terminates by joining great cerebral vein

Blood supply of Cerebellum: -superior surface is supplied by superior cerebellar branches of basilar artery -anterior part of inferior surface is supplied by anterior inferior cerebellar branch of same artery -posterior part of inferior surface is supplied by posterior inferior cerebellar artery. -venous drainage to neighbouring venous sinuses.

Blood supply of Brain Stem: -is supplied by branches from posterior cerebral arteries, including their central branches both posteromedial & posterolateral. -pons is supplied by pontine branches of basilar artery. -medulla is supplied by medullary branches of vertebral artery and branch from posterior inferior cerebellar artery -veins of brainstem drain into neighbouring venous sinuses

Clinical Anatomy -hemiplegia-due to internal capsule lesion caused by thrombosis of lenticulostriate branches of MCA. -lenticulostriate branch is also most frequently ruptured and cause cerebral hemorrhage. Lesion causes hemiplegia, deep coma & ultimately death. -upper monoplegia is caused by thrombosis of Heubner’s recurrent branch of ACA. -thrombosis of terminal cortical branch of ACA causes lower hemiplegia. -thrombosis of posterior inferior cerebellar artery causes lateral medullary syndrome (Wallenberg’s syndrome) – chracterised by severe giddiness, dsyphagia, crossed hemianesthesia, Horner’s syndrome, cerebellar symptoms.

Clinical Anatomy -pontine hemorrhage is charaterized by contralateral hemiplegia, deep coma , pinpoint pupil, hyperpyrexia. -cerebral vascular disease is quite common in old age due to hemorrhage, thrombosis & embolism -hypertensive encephalopathy, elevation of diastolic pressure is form a multiple small lesions all over cirlce of Willis..knowna as Berry aneurysm