The brain receives its blood supply from two pairs of arteries - the internal carotid arteries and the vertebral arteries. The internal carotid arteries enter the cranium and give off branches including the anterior cerebral artery and middle cerebral artery. The vertebral arteries join to form the basilar artery which also gives off branches. These arteries anastomose to form the Circle of Willis, which ensures adequate blood flow to the brain. Obstructions in different arteries can cause deficits in specific brain regions due to the territories each supplies. Veins drain blood from the brain into dural sinuses.

1. Blood Supply of the Brain
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Arterial supply
• The brain is supplied by 2 pairs of arteries
• rt & lt internal carotid artery (ICA)
• rt & lt vertebral arteries
A. Internal carotid artery
• arises in the neck as one of the 2 terminal branches
of the C.C.A.
• has four parts
–Cervical part
–Interapetrous part
–Intracavernous part
–Intracranial part

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• Each I.C.A leaves the cavernous sinus by piercing the
dura mater and ascends in the subarachnoid space lat.
to the optic chiasma
• In the subarachnoid space each gives off the following
branches:
– Ophthalmic: which enters the optic canal below optic nerve
to supply the orbit
– Posterior communicating: which Joins the post. cerebral to
establish the circle of Willis
– Anterior choroidal: which supplies the choroid plexus of the
lat. ventricle.
• It ends below the ant. perforated substances of the
brain by dividing into 2 terminal branches:
– The ant. cerebral a (the smaller branch)
– The middle cerebral a (the larger branch)

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6. Clinical importance
• the A.C.A supplies 3 important regions;
– The motor & sensory areas of the lower limb in the
paracentral lobule
– The septal region where a small lesion may result in
prolonged unconsciousness
– The corpus callosum
obliteration of its blood supply may result in apraxia
(inability to perform purposeful movements in spite
of intact muscle

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Middle Cerebral artery (M.C.A)
• arises below the ant. perforated substance as the
larger of the 2 terminal branches of I.C.A
• ends on the surface of the insula by breaking up
into many terminal branches

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10. Clinical importance:
• the M.C.A supplies:
– the motor & sensory areas for the whole body except
the lower limbs
– the auditory area in the sup. temporal gyrus
– motor speech area in the inf. frontal gyrus
– most of the internal capsule
Obstruction of its blood supply----Hemiplegia

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B. The Vertebro-basilar System
• Vertebral artery
– each vertebral a arises in the root of the neck as a
branch from the 1st part of subclavian
– enters the cranial cavity through the foramen magnum
• Inside the skull, the rt & lt arteries unite at the
lower border of the pons to form the basilar artery.
• The vertebral arteries enter the cranial cavity & give
rise to 2 terminal branches:
– a medial terminal br. supplying the inf. vermis of the
cerebellum
– a lateral terminal br. supplying the post. part of inf.
surface of cerebellum

13. Clinical importance of P.C.A:
• its supplies:
– the centre of smell in the uncus.
– the whole visual cortex in the occipital lobe
– most of thalamus
– most of the midbrain
– most of the choroids plexus of the 3rd & lat. ventricles.
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Circulus arteriosus of Willis
• it is an arterial anastomosis b/n arteries supplying
the brain
• located in the interpeduncular cistern around the
interpeduncular fossa.

15. Desalegn Tadesse, Jimma University 15

16. Desalegn Tadesse, Jimma University 16

17. • The following arteries enter in the formation:
– Rt. & Lt. anterior cerebral arteries
– the ant. communicating a . connecting the 2 cerebral arteries
– the Rt. & Lt. ICA
– the Rt. & Lt. post communicating aa. branches of ICA
– The rt and lf post cerebral arteries

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Venous Drainage of the Brain (the veins are thin walled &
valveless)
• The superior cerebral veins drain into the superior
sagittal sinus
• Inferior and superficial middle cerebral veins drain into
the straight, transverse, and superior petrosal sinuses.
• The great cerebral vein (of Galen) is a single, midline
vein formed inside the brain by the union of two
internal cerebral veins;
– it ends by merging with the inferior sagittal sinus to form the
straight sinus
• The superior and inferior cerebellar veins drain from
the cerebellum into the transverse and sigmoid sinuses.

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