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. Blood Supply of the Brain
The brain is supplied by:
Two internal carotid arteries
Two vertebral arteries.
They lie within subarachnoid space
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 bone.
Then pass through cavernous sinus and perforates the dura mater and enters the subarachnoid space .
At the medial end of the lateral cerebral sulcus it divides into :
Anterior cerebral artery
Middle cerebral artery

6. Branches of internal carotid artery
Ophthalmic artery supplies:
The eye
Frontal area of scalp
Ethmoid and frontal sinuses
Dorsum of nose.
Posterior communicating artery join the posterior cerebral artery, forming part of circle of Willis.

7. Choroidal artery
Enters inferior horn of lateral ventricle to form choroid plexus.
It gives branches to:
Crus cerebri
Lateral geniculate body
Optic tract
Internal capsule.

8. Anterior cerebral artery
It enters longitudinal fissure of the cerebrum where it joins artery of opposite side by anterior communicating artery.
Cortical branches supply:
All the medial surface of the cerebrum till parieto-occipital sulcus
1 inch of lateral surface (leg area).
Central branches supply:
Parts of lentiform
Caudate nuclei
Internal capsule.

9. Middle cerebral artery
It is largest branch of internal carotid, runs in lateral cerebral sulcus.
Its cortical branches supply:
Entire lateral & orbital surfaces of cortex
Except:
1 inch of lateral supplied by anterior cerebral artery
Occipital pole and inferolateral surface of hemisphere supplied by posterior cerebral artery
Thus supplies all body except the (leg area).

10. Central branches enter the anterior perforated substance and supply the:
Lentiform and caudate nuclei
Internal capsule

11. Vertebral Artery:
Branch of the first part of subclavian artery
Passes through foramina transverseria of the upper six cervical vertebrae
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.

12. Branches of vertebral artery:
Meningeal branches supply bone and dura in posterior cranial fossa.
Posterior spinal artery.
Anterior spinal artery.
Posterior inferior cerebellar artery largest branch of vertebral which supplies:
Cerebellum
Medulla oblongata
Choroid plexus of fourth ventricle.
Medullary arteries to medulla oblongata.

13. 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 cerebellar artery(AICA) for cerebellum,pons & upper medulla.
Superior cerebellar artery for cerebellum,pons & pineal gland.

15. 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).

16. Its central branches supply:
Thalamus
Lentiform nucleus
Midbrain
Pineal gland
Medial geniculate bodies.
Choroidal branch for choroid plexus of lateral & third ventricles.

17. Circle of Willis:
It lies in the interpeduncular fossa at 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.

18. Arteries to specific brain areas:
Corpus striatum and internal capsule supplied mainly by medial and lateral striate central branches of middle cerebral artery plus central branches of anterior cerebral artery.
Thalamus is supplied mainly by posterior communicating, basilar, and posterior cerebral arteries.
Midbrain is supplied by posterior cerebral, superior cerebellar, and basilar arteries.

19. Pons is supplied by basilar and anterior, inferior, and superior cerebellar arteries.
Medulla oblongata is supplied by vertebral, anterior and posterior spinal, posterior inferior cerebellar, and basilar arteries.
Cerebellum is supplied by superior cerebellar, anterior inferior cerebellar, and posterior inferior cerebellar arteries.

20. 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.

21. 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.
Emissary veins connect the dural venous sinuses with the diploic veins of the skull and with the veins of the scalp

23. 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.

24. 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 .

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

26. Veins of specific brain areas:
Midbrain is drained by veins that open into the basal or great cerebral veins.
Pons is drained by veins that open into basal vein, cerebellar veins.
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.

27. Dural venous sinuses
The dural venous sinuses are endothelial-lined spaces between the outer periosteal and the inner meningeal layers of the dura mater
They finally drain into internal jugular veins
Emptying into the dural venous sinuses are diploic vein and emissary veins.

28. The dural venous sinuses
Superior sagittal sinus
Inferior sagittal sinus
Straight sinus
Transverse sinuses
Sigmoid sinuses
Occipital sinuses
Confluence of sinuses
Superior petrosal
Inferior petrosal
Cavernous sinuses

30. The superior sagittal sinus
Deviates ,usually the right & becomes continuous with the right transverse sinus.
It communicates with venous lacunae on each side.
Numerous arachnoid villi and granulations project into the lacunae
It usually becomes continuous with the right transverse sinus.

31. At the internal occipital protuberance, it is dilated to form the confluence of the sinuses
It receives :
The superior cerebral veins
The occipital sinus
Diploic & emissary veins
CSF(through arachnoid granulations)

32. The inferior sagittal sinus
Joins the great cerebral vein to form the straight sinus
It receives a few cerebral veins from the medial surface of the cerebral hemispheres.

33. The straight sinus
Is formed by the union of the inferior sagittal sinus with the great cerebral vein.
It ends by turning to the left (sometimes to the right) to form the transverse sinus.
It receives:
Inferior sagittal sinus
Great cerebral vein, posterior cerebral veins
Superior cerebellar veins
Veins from the falx cerebri

34. The transverse sinuses
Are paired structures that begins at the internal occipital protuberance
The right sinus is usually continuous with the superior sagittal sinus, and the left is continuous with the straight sinus.
The transverse sinuses receive the:
Superior petrosal sinuses
Inferior cerebral
Cerebellar veins
Diploic veins.
They end by turning downward as the sigmoid sinuses .

35. The sigmoid sinuses
Are a direct continuation of the transverse sinuses.
The sinus then reaches the posterior part of the jugular foramen to become continuous with the superior bulb of the internal jugular vein.
The occipital sinus
Is a small sinus occupying the attached margin of the falx cerebelli.
It communicates with the internal vertebral venous plexus
Drains into the confluence of sinuses.

37. The cavernous sinuses
Are situated in the middle cranial fossa on each side of the body of the sphenoid bone
The two sinuses communicate with each other by anterior and posterior intercavernous sinuses cerebri .

39. The cavernous sinus receives:
Cerebral and ophthalmic veins
Emissary veins from pterygoid plexus of veins
Sphenoparietal sinuses
It has important communication with the facial vein through the superior ophthalmic vein. (This is a route by which infection can travel from the facial skin to the cavernous sinus.)

41. Structures passing through each cavernous sinus are:
The internal carotid artery;
The abducent nerve [VI].
Structures in the lateral wall of cavernous sinus are the :
Oculomotor nerve [III];
Trochlear nerve [IV];
Ophthalmic nerve [V1];
Maxillary nerve [V2].

42. The superior and inferior petrosal sinuses
Are small sinuses situated on the superior and inferior borders of the petrous part of the temporal bone .
Superior sinuses drain the cavernous sinus into the transverse sinus.
Inferior sinuses drains the cavernous sinus into the internal jugular vein.

43. 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 arteries that arise from arteries outside the vertebral column.

44. Each segmental spinal artery gives rise to anterior and posterior radicular arteries
The great anterior medullary artery of Adamkiewicz , that arise from the aorta, enters the vertebral canal and anastomoses with the anterior and posterior spinal arteries.

45. Veins of the Spinal Cord
The veins of the spinal cord drain into six tortuous longitudinal channels that communicate within the skull with the veins of the brain and the venous sinuses.
They drain mainly into the internal vertebral venous plexus.