The Blood Supply of the Brain and Spinal Cord

2. The Blood Supply of the Brain and Spinal Cord Dr. Nimir Dr. Safaa

3. Objectives • Describe the four arteries supplying the CNS. • Follow up each artery to its destination. • Describe the circle of Willis and its branches. • Discuss the principle of end artery type of circulation. • Describe venous drainage of the brain.

4. The brain is supplied by two internal carotid &two vertebral arteries. • They lie within subarachnoid space, and their branches anastomose on inferior surface of brain to form circle of Willis.

5. Internal Carotid Artery: • It begins at the bifurcation of the common carotid artery, where it has the carotid sinus. It ascends by passing through the carotid canal of the temporal throubone.Then pass through cavernous sinus and perforates the duramaterand enters the subarachnoid space . • At the medial end of the lateral cerebral sulcus it divides into anterior and middle cerebral arteries

6. Brnches of internal carotid artery: • Ophthalmic artery supplies the eye and its terminal branches supply frontal area of scalp, ethmoid and frontal sinuses, and dorsum of nose. • Posterior communicating artery join the posterior cerebral artery, forming part of circle of Willis. • Choroidal artery enters inferior horn of lateral ventricle to form choroid plexus. It gives branches to cruscerebri,lateralgeniculate body, optic tract, and internal capsule.

7. Anterior cerebral artery enters longitudinal fissure of the cerebrum where it joines artery of opposite side by anterior communicating artery. • Its cortical branches supply all the medial surface of the cerebral till parieto-occipital sulcus and 1 inch of lateral surface (leg area). • Central branches supply parts of lentiform, caudate nuclei and internal capsule.

8. Middle cerebral artery, largest branch of internal carotid, runs in lateral cerebral sulcus. • Its cortical branches supply entire lateral & orbitalsurfaces ofcortex except 1 inch of lateral supplied by anterior cerebral, occipital pole, and inferolateral surface of hemisphere supplied by posterior cerebral artery thus supplies all body except the (leg area).

9. Vertebral Artery: • Branch of the first part of subclavian artery, passes through foramina transverseria of the upper six cervical vertebrae and enters skull through foramen magnum. • At the lower border of the pons, it joins the vessel of the opposite side to form the basilar artery.

10. Branches of vertebral artery: • Meningeal branches supply bone and dura in posterior cranial fossa. • Posterior spinal artery. • Anterior spinal artery. • Posterior inferior cerebellarartery largest branch of vertebral which supplies cerebellum, medulla oblongata and choroid plexus of fourth ventricle. • Medullaryarteries to medulla oblongata.

11. Basilar Artery: • It is formed by union of the two vertebral arteries at the pons. • Its branches are: • Pontine arteries to pons. • Labyrinthine artery to internal ear. • Anterior inferior cerebellarartery for cerebellum,pons & upper medulla. • Superior cerebellarartery for cerebellum,pons & pineal gland.

12. Posterior cerebral artery is joined by posterior communicating branch of internal carotid. • Its cortical branches supply inferolateral & medial surfaces of temporal lobe, lateral & medial surfaces of occipital lobe (visual cortex). • Its central branches supply thalamus, lentiformnucleus,midbrain,pineal gland and medial geniculate bodies. • Choroidal branch for choroid plexus of lateral & third ventricles.

13. Circle of Willis: • It lies in the interpeduncularfossaat the base of the brain. • It is formed by the anastomosis between the two internal carotid arteries and the two vertebral arteries. • It allows blood that enters by either internal carotid or vertebral arteries to be distributed to any part of both cerebral hemispheres.

14. Arteries to specific brain areas: • Corpus striatum and internal capsule supplied mainly by medial and lateral striate central branches of middle cerebral artery pluss central branches of anterior cerebral artery. • Thalamusis supplied mainly by posterior communicating, basilar, and posterior cerebral arteries. • Midbrainis supplied by posterior cerebral, superior cerebellar, and basilar arteries. • Ponsis supplied bybasilar and anterior, inferior, and superior cerebellararteries. • Medulla oblongata is supplied by vertebral, anterior and posterior spinal, posterior inferior cerebellar, and basilar arteries. • Cerebellumis supplied by superior cerebellar, anterior inferior cerebellar, and posterior inferior cerebellararteries.

15. End arteries (terminal): • Anatomic (True) End Artery: No anastomoses. • Functional End Artery: Ineffectual anastomoses. • An example of a true terminal arteries is that which supplies the retina. • Functional end arteries supply segments of the brain.

16. Veins of the Brain: • They have no muscular tissue in their walls, and they have no valves. They lie in subarachnoid space. They drain into the cranial (dural) venous sinuses.

17. Cerebral veins divided into: • External Cerebral Veins: • Superior cerebral veins drains superolateral& medial surfaces and empty into the superior sagittal sinus. • Superficial middle cerebral vein drains the lateral surface of the cerebral hemisphere & empties into the cavernous sinus. • Deep middle cerebral vein drains insula and is joined by anterior cerebral and striate veins to form the basal vein. Basal vein joins the great cerebral vein, which in turn drains into straight sinus .

18. Internal Cerebral Veins • There are two internal cerebral veins. • They are formed by union of the thalamostriate vein and choroid vein then unite to form the great cerebral vein, which joined with basal veins & empties into the straight sinus.

19. Veins of specific brain areas: • Midbrainis drained by veins that open into the basal or great cerebral veins. • Ponsis drained by veins that open into basal vein, cerebellarveins. • Medulla oblongata is drained by veins that open into spinal veins. • Cerebellum is drained by veins that empty into great cerebral vein or adjacent venous sinuses.

20. Blood Supply of the Spinal Cord: • It is supplied by three arteries: • Two posterior spinal arteries from vertebral arteries. • Anterior spinal artery from union of two arteries from vertebral artery . • Spinal arteries are reinforced by segmental arteriesthat arise from arteries outside the vertebral column.