Blood supply of Human Brain

1. Dr. Amjad PT

3.  The consequences of stroke depend upon which areas
of the brain are affected by ischemia, hemorrhage,
hematoma or aneurysm. Therefore, it is important to
understand the organization of the cerebral blood
supply system.
 Two arterial systems supply the brain with blood: the
internal carotid and vertebral. The internal
carotids and vertebro-basilar arteries are connected
via the circle of Willis, which allows blood to pass
from one system to another in the event of blockage.

4. C1
C2
C3
C4
C5
C6
C7
ant. clinoid proc.
cavernous sinus
foramen lacerum
carotid canal

5. The Internal Carotid Arteries
There are two internal carotid arteries. They ascend from
the aortic arch toward the brain along each side of the
neck. They pass behind the ear into the temporal
lobe and enter the subarachnoid space. They then go to
the circle of Willis where each bifurcates to form two
main branches: the anterior cerebral artery and
the middle cerebral artery. The course of the internal
carotid arteries and their branches is tortuous.
Because of their many twists and turns these arteries
are all subject to blockages caused by cholesterol
build-up. For this reason, the internal carotids, and
the middle and anterior cerebral arteries are more
vulnerable to ischemic rather than hemorrhagic
stroke.

6.  The contralateral internal carotid may use the circle of Willis/anterior
communicating artery to supply blood to both pairs of anterior and
middle cerebral arteries. Complete interruption of blood flow in the
anterior cerebral artery is not very likely because the opposite anterior
cerebral can use the anterior communicating artery to make up for the
deficiency.
 A patient who has suffered such a blockage might have a paralyzed leg
or be incontinent of bowel and/or bladder. Since the parts of the motor
and sensory strips connected to the arm receive some blood from the
anterior cerebral artery, the arm may also be somewhat affected by this
kind of blockage. Finally, apraxia of gait may also occur if an anterior
cerebral artery fails to supply an adequate amount of blood to the
medial part of the motor strip.
The anterior cerebral arteries also supply blood to the anterior aspects
of the frontal lobes. As these areas are involved in higher level cognition
such as reasoning and judgment, a condition called cerebral dementia
may result from anterior cerebral artery blockages. Confused
language..

8.  Anterior cerebral arteries
 smaller terminal branch of the ICA
 enters longitudinal fissure
 connected to the opposite anterior cerebral artery by
anterior communicating artery (part of the CoW)
 curves over corpus callosum
– central branch supply deep masses of gray matter in the
cerebral hemisphere
– Supply:
• cortical branches supply all medial surface of cerebral cortex
up to parieto-occipital sulcus
• corpus callosum
• approximately 1 inch of the frontal and parietal cortex on the
superior aspect of their lateral surface (this include the leg
area of the precentral gyrus)
• anterior portions of the basal ganglia and internal capsule

10.  Middle Cerebral Arteries
 These large arteries have tree-like branches that bring
blood to most of the lateral cortex of each cerebral
hemisphere. This means that the middle cerebral arteries
supply blood to the cortical areas involved in speech,
language and swallowing
 runs laterally in the lateral sulcus
 cortical branches supply entire lateral surface of the
hemisphere EXCEPT
 area supplied by anterior cerebral artery
 inferolateral surface supplied by posterior cerebral artery
 occipital pole
 supply all motor area except “leg area”
 supply parts of the internal capsule and basal ganglia
 central branches supply deep masses of gray matter within
the cerebral hemisphere

11. If the left middle cerebral artery is
blocked, aphasia and apraxia may
occur.
Blockages of the right middle cerebral
artery can cause left side neglect,
which is an impairment in the ability to
recognize and respond to stimuli on the
left side of the body, prosopagnosia or
the inability to recognize faces, and
various cognitive problems,
including agnosia. All of these are part
of the right hemisphere syndrome.

12. pituitary stalk
pituitary stalk
optic chiasm
oculomotor n.
mamillary bodies
abducens n.

13. • Ophthalmic artery
– enters orbit through optic canal, below and lateral to
optic nerve
– supplies the eye, including retina and optic nerve
• Posterior communicating artery
– runs backward to join posterior cerebral artery at
interpeduncular fossa
• deep depression on inferior of midbrain between cerebral
peduncles
• part of the circle of willis
 Choroidal artery
 enter inferior horn of lateral ventricle to supply choroid
plexus
 branches may help supply the optic tract, LGB, internal
capsule and crus cerebri

14.  branch of the 1st part of the subclavian artery
 Both of the vertebral arteries ascend through the spinal
column and enter the brain through the magnum foramen.
Once in the brain, they continue to ascend, traveling beside
the brain stem. At the lower border of the pons the two
vertebral arteries join together to form the basilar
artery or vertebro-basilar artery.
 Cranial branches
– meningeal arteries
– anterior and posterior spinal arteries
– posteroinferior cerebellar artery
• largest branch of the vertebral artery and supplies parts of the
cerebellum and the dorsolateral portion of the rostral medulla
– medullary arteries
• along with posteroinferior cerebellar artery, supply most of the
medulla

15.  at lower border of pons, vertebral arteries unite to form the BASILAR
ARTERY
 ascends along the ventral midline of the pons and terminates near the
rostral border of pons by dividing into 2 posterior cerebral arteries
 Vertebrobasilar arterial system
 posterior circulation of brain
 Branches:
 branches to pons, cerebellum, internal ear
 labyrinthine artery
 follows the course of the CN VIII and supplies inner ear
 anterior inferior cerebellar artery
 supplies part of the pons and the anterior and inferior regions of
the cerebellum
 superior cerebellar artery
 supplies part of the rostral pons and superior region of the
cerebellum
 pontine branches
 supply most of pons

17.  Posterior Cerebral Arteries
 formed by the terminal bifurcation of the basilar artery
 anastomoses with the posterior communicating artery in the CoW
 Supply:
 lateral surface of the hemisphere – occipital pole and inferior
temporal lobe
 medial surface of the hemisphere – occipital lobe and posterior
2/3 of temporal lobe
 At the superior border of the pons, the basilar artery divides to
form the two posterior cerebral arteries. These arteries
supply blood to the part of the brain that lies in the posterior
fossa of the skull, including the medial aspects of the occipital
lobes, the inferior portions of the temporal lobes, the
brainstem, and the cerebellum. They also deliver blood to the
thalamus and some other subcortical structures. A vascular
lesion may result in Thalamic Aphasia or Thalamic Syndrome
 The basilar and posterior cerebral arteries may hemorrhage
due to shearing injuries caused by accidents or pressure due to
edema of the brain.

18. Since they provide blood to
the occipital lobes, damage
to these arteries can cause a
variety of visual problems,
including cortical blindness,
which is an inability to read
and visual agnosia, or the
inability to recognize stimuli
presented visually. Because
these arteries supply blood to
the cerebellum and to the
brain stem, blockages or
hemorrhaging there can
cause
either ataxic (cerebellar) or
flaccid (lower motor neuron)
dysarthria..

19. • located at base of brain
• anterior part lies in front of optic chiasm
• posterior part situated just below the mamillary bodies
• allows for excellent collateral circulation
– occlusion of an individual artery
• often completely compensated by collateral circulation through the
CoW
 Formed by:
 terminal part of the ICA
 proximal parts of the anterior, middle and posterior cerebral
arteries
 anterior and posterior communicating arteries

20. 1 – Vertebral artery
2 – AICA
3 – Basilar artery
4 – Superior cerebellar artery
5 – Posterior cerebral artery
6 – Posterior communicating artery
7 – Middle cerebral artery
8 – ICA
9 – Opthalmic artery
10 – Anterior cerebral artery
11 – Anterior communicating artery
12 – Hypothalamic artery
13 – Anterior choroidal artery

23.  In the Circle of Willis the two internal carotids are joined together by
the anterior communicating artery while the posterior communicating
artery links the internal carotid system with the basilar artery. These
connections make collateral circulation, which Love and Webb define as
"the flow of blood through an alternate route," possible. This is a safety
mechanism, allowing brain areas to continue receiving adequate blood
supply even when there is a blockage somewhere in an arterial system.
When all arteries are functioning normally, their blood supplies will not
mix where they meet in the Circle because the pressure of their streams
will be equal.
 As long as the Circle of Willis can maintain blood pressure at fifty
percent of its normal level, no infarction or death of tissue will occur in
an area where a blockage exists. If collateral circulation is good,
sometimes a blockage will have no permanent effects. Sometimes, an
adjustment time is required before collateral circulation can reach a
level that supports normal functioning; the communicating arteries will
enlarge as blood flow through them increases. In such cases, a transient
ischemic attack may occur, meaning that parts of the brain are
temporarily deprived of oxygen.

24. • veins of the brain have no muscular tissue in the wall
and no valves
• Veins – Located in the SAS
• Venous sinuses – located between 2 layers of the Dura
• superficial and deep veins of the brain drain into the
dural venous sinuses (which in turn drain into the
internal jugular veins)
• Superficial veins
– drain the cortex and the more superficial hemispheric
white mater mainly into the superior sagittal and
cavernous sinuses

25. • Deep or internal veins
– drain the deep hemispheric white mater and basal
ganglia into the 2 internal cerebral veins which unite to
form the great cerebral vein
• Great cerebral vein
– formed by the union of 2 internal cerebral veins and
drains into the straight sinus