1. Role of Blood Supply Nutrition to parenchyma (brain cells).
Brain is completely dependent on oxygen supply - No O2 reserves.
Irreversible damage in 4-6 minutes if no oxygen
Brain requires 20% of O2 for 2% of body weight.
Brain requires glucose for energy
No ability to use fat
Remove carbon dioxide and waste-products from cells
Cerebral perfusion
> 60 ml/100gr min-1 in Gray matter
40 < X < 60 in White matter
750mL blood pumped per minute and circulated blood returned for reoxygenation

2. Network of arteries and veins
Vascular Network
Network of arteries and veins
Arteries carry blood away from the heart
Arteries divide into smaller vessels called: arterioles
Arterioles divide further into capillaries
Vascular Network
Veins carry blood toward the heart
Smallest level are venules that are connected to capillaries
Venules Carry blood to sinuses on cortical surface

3. Local blood flow
Arteries
Arterioles
Capillaries
Venules
Sinuses

4. Cerebrovascular Supply
Two Systems
Carotid System
Vertebral Basilar System
Meet in Circle of Willis

5. Vertebral / Basilar Arteries
Brain stem
Basilar Artery
Vertebral Arteries

6. Vertebral Basilar System
Two Vertebral Arteries enter skull through Foramen Magnum
Join to form the Basilar Artery and then Circle of Willis
Numerous small branches
Supplies the brainstem and cerebellum
Posterior Inferior Cerebellar Artery (PICA) is one that serves cerebellum.

7. Carotid Arteries

8. Carotid System Common Carotid Artery Divides into two branches
External Branch
Supply blood to facial muscles, forehead and oral, nasal and orbital cavities
Internal Branch (enters the skull through the carotid foramen)
Anterior choroidal artery (supplies optic tract, posterior limb of internal capsule, branches to midbrain,and lateral geniculate nucleus).
Ophthalmic artery (Supplies blood to the eyeball and ocular muscles)
Major source of blood to the brain
After joining Circle of Willis becomes anterior cerebral and middle cerebral arteries

9. Circle of Willis

10. Wreath-shaped circle of Willis located at ventral surface of brain
Connects Carotid and Vertebral Basilar Systems
Middle and Anterior Cerebral Arteries
Anterior Communicating Artery
Posterior Cerebral Artery
Posterior Communicating Artery

11. Cortical Blood Supply ACA: Medial Frontal Perfusion
MCA: Lateral Perfusion
PCA: Posterior medial Perfusion, cerebellum
Watershed Areas: overlap between major arteries
Major Arteries
 Carotid
 Anterior Cerebral
 Middle Cerebral
Posterior Cerebral

12. Cortical (Circumferential) Branches Central (Penetrating) Branches
Two Types of Arteries
Cortical (Circumferential) Branches
Supply External Brain Structures
Central (Penetrating) Branches
Small
Penetrate ventral surface to supply internal brain structures

13. Anterior Cerebral Artery
Supplies Orbital and Medial Surfaces of Frontal and Parietal Lobes
Interruption causes
Cortical Arteries
Paralysis of legs and feet
Difficulty in prefrontal lobe functions of cognitive thinking, judgment, motor initiation and self monitoring

14. Middle Cerebral Artery
Direct continuation of carotid artery
Cortical Branches
Temporal
Parietal
Frontal

15. MCA: Cortical Branches
Supplies blood to entire lateral surface of brain
Somatosensory Cortex
Motor Cortex
Broca's Area
Heschl’s Gyrus
Wernicke’s Area
Therefore, symptoms include
Aphasia
Motor deficits
Neglect (right hemisphere)

16. MCA – Penetrating Arteries
Supplies basal ganglia and diencephalon
Interruption causes
Contralateral hemiplegia
Impaired sensory systems
Touch
Pain and temperature

17. Central Penetrating Arteries
Arise from cortical arteries or from Circle of Willis
Penetrate inferior surface of brain
Can form channels to facilitate blood supply
Central (Penetrating) Arteries
Supply
Thalamus
Hypothalamus
Basal Ganglia
Internal capsule
Choroid Plexus

18. Posterior Cerebral Artery
Supplies blood to anterior and inferior temporal lobes, uncus, inferior temporal gyri, inferior and medial occipital lobe
Watersheds with middle cerebral artery
Interruption causes
Homonymous hemianopsia
Possible total blindness
Cerebellar symptoms

19. Collateral Circulation
Redundant arteries provide alternative supply when primary supply is lost
Small, normally closed arteries open up after occlusion, connecting two larger arteries or different parts of the same artery.
Dependent on location and severity of blockage
Better collateral circulation if blockage is near main trunk
Better if blockage occurs gradually

20. Hemorrhagic (Bleed). 20% of strokes are due to arteries rupturing.
Vascular Pathologies
Occlusive (Something is blocked causing ischemia). 80% of strokes are ischemic
Embolism: object from another part of the body which travels through artery until it gets stuck.
Thrombosis: object originating within a blood vessel: local buildup of fatty substances usually at a bifurcation of artery, these can rupture leading to catastrophic blockage
Hemorrhagic (Bleed). 20% of strokes are due to arteries rupturing.

21. Risk factor for ischemic stroke
Atherosclerosis from reduced lumen due to lipids, calcium fatty particles etc. (‘Athera’ = porridge in Greek)
A form of Arteriosclerosis: a general term describing any hardening (and loss of elasticity) of arteries.
Leads to stenosis (narrowing) of the artery, gradually leading to insufficient blood supply
Plaques can rupture, creating a thrombus in blood supply

22. Vascular Pathologies - Bleeds
Hemorrhagic
Bleeding from ruptured vessels
Types
Intracerebral: More common in thalamus and basal ganglia
Subdural
Aneurysm
Aneurysm

23. Haemorrhages 20% of strokes are bleeds
Typically, due to ruptured aneurysm
An aneurysm is a sac-like protrusion of an artery caused by a weakened area within the vessel wall.
Introspectively, the worst headache of your life.
Surgery to clip aneurysm can save patients life.
CT of recent haemorrhage

24. Arteriovenous Malformations
AVMs can cause hemorrhagic strokes
Tangled web of arteries and veins present since birth

25. Blood returns to lungs for oxygen Drain into Sinus System
Venous Sinus System
Blood returns to lungs for oxygen
Drain into Sinus System
Dural Sinuses
Superior Sagittal Sinus
Inferior Sagittal Sinus
Straight Sinus
Transverse Sinus
Cavernous Sinus
Petrosal Sinuses

26. Notes Regulation of Cerebral Blood Flow Blood-Brain Barrier
Closed system under constant pressure
Controlled by elasticity of blood vessels, and metabolic needs
Aging can cause less elasticity responsiveness and eveness of flow
Blood-Brain Barrier
Tight system does not allow direct contact of all brain tissues with blood
Specialized system to extract needed molecules
May impede medicine entering the brain