Blood supply

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Blood Supply of the Brain 1- Internal carotid
arteries -They arises from the common
carotid arteries and enter the middle fossa of
the cranial cavity through the carotid canal
which opens into the side of the foramen lacerum
above the closed inferior opening. - It
turns upward to reach the side of the body of
sphenoid bone. It then turns forward in the
cavernous sinus to reach the medial aspect of the
anterior clinoid process and lies lateral to the
optic chiasma. - Its course follows a
series of bends ( carotid syphon ). Branches (
internal carotid system ) 1- Hypophyseal
arteries -They arise from the intracavernous
section of the internal carotid to supply the
neurohypophysis. -They also form the
pituitary portal system of vessels by which
releasing factors are carried from the
hypothalamus to adenohypophysis.
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2- Ophthalmic artery - It passes into the
orbit through the optic foramen. - It
supplies the structures of the orbit, frontal and
ethmoidal sinuses, frontal part of the scalp and
dorsum of the nose. 3- Anterior choroidal
artery - It supplies the optic tract,
choroid plexus of the lateral ventricle,
hippocampus and some of the deep structures of
the hemisphere, including the internal capsule
and globus pallidus. 4- Anterior cerebral
artery - It passes medially above the
optic nerve and then passes into the great
longitudinal fissure between the frontal lobes
where it joins the corresponding vessels of the
opposite side by anterior communicating artery.
- It follows the curvature of corpus
callosum within the great longitudinal fissure.
It ramifying over the medial surface of the
frontal and parietal lobes and supplies them.
Also, branches extend out of the great
longitudinal fissure to supply a narrow lateral
band of frontal and parietal cortices.
-The territory supplied by it includes the motor
and sensory cortices for the lower limb.
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• 5- Posterior communicating artery
• - It passes backwards to join the
• posterior cerebral artery.
• 6- Middle cerebral artery
• - It is the largest branch of the 3 cerebral
  arteries and its cortical territory is the
  largest. It passes laterally to enter the lateral
  fissure within which it subdivides.
• - Its branches supply the whole of the
  lateral surface of the frontal, parietal and
  temporal lobes except those areas which are
  supplied by the anterior cerebral artery.
• - It supplies the primary motor and sensory
  cortices for the whole body excluding the lower
  limb. The auditory cortex and the insula in the
  depth of the lateral fissure.

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Vertebral Artery - It arises from the 1st part
of subclavian artery and ascends through the
foramina transversaria of the upper 6 cervical
vertebrae and enters the cranial cavity through
foramen magnum along side the ventrolateral
aspect of the medulla. - Along its course, it
gives rise to a number of branches including the
anterior and posterior spinal arteries which
supply the medulla and spinal cord. - Its
largest branch is the posterior inferior
cerebellar artery which supplies the inferior
aspect of the cerebellum. -The 2 vertebral
arteries unite at the junction between medulla
and pons to form the basilar artery which runs
the length of the pons and supplies it by pontine
branches. At the junction of pons and midbrain it
divides into 2 pairs of vessels, the superior
cerebellar arteries and the posterior cerebral
arteries. N.B. The brain stem, cerebellum and
occipital lobe are supplied by the
vertebrobasilar system.
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• Branches of Basilar Artery
• Pontine arteries
• Anterior inferior cerebellar artery
• It supplies the anterior and inferior
  portion of the cerebellum.
• 3. Labyrinthine artery
• It passes into the internal acoustic meatus
  to supply the inner ear.
• 4. Superior cerebellar artery
• It supplies the superior aspect of the
  cerebellum.
• 5. Posterior cerebral artery
• It curves around the midbrain to supply the
  visual cortex of the occipital lobe and the
  infero medial aspect of the temporal lobe.

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The internal carotid and vertebrobasilar
systems are joined by 2 thin vessels which are
the posterior communicating arteries. They pass
rostrocaudally between the ends of the posterior
cerebral and the internal carotid
arteries. Circle of Willis - It is an
arterial anastomosis in the interpeduncular fossa
at the base of the brain. This fossa is formed
anteriorly by optic chiasma. Posteriorly by the
upper border of the pons. Anterolaterally by the
2 optic tracts. Posterolaterally by the 2
cerebral peduncles. - It is formed of
Anterior cerebral anterior communicating
internal carotid posterior communicating and
posterior cerebral arteries.
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From the arteries of circle of Willis
numerous small vessels penetrate the surface of
the brain. These are perforating arteries (
central or ganglionic ). 1- Anterior
perforating arteries They arise from the
anterior cerebral artery. Anterior
communicating artery and the region
of origin of the middle cerebral artery. They
enter the brain in the region between the optic
chiasma and termination of the olfactory tract (
anterior perforated substance ). They supply
basal ganglia, optic chiasma, internal capsule
and hypothalamus. 2- Posterior perforating
arteries They arise from the posterior
cerebral and
posterior communicating arteries. They enter the
brain ( posterior perforating substance ) to
supply the ventral portion of the midbrain and
parts of the subthalamus and hypothalamus.
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• Venous Drainage of the Brain
• 1- Superficial veins
• They lie within the subarachnoid space.
• Superior cerebral veins
• They drain the lateral surface of the
  cerebral hemispheres and empty into the superior
  sagittal sinus.
• b. The superficial middle cerebral vein
  It runs along the line of the lateral fissure
  and empties into the cavernous sinus.
• c. Superior ( great ) anastomotic vein
  It drains into the superior sagittal sinus.
• d. Inferior anastomotic vein
  It drains into the transverse sinus.
• N.B. The circular sinus is a venous circle
  around the hypophysis.

C
A
B
D
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2- Deep cerebral veins -They drain the
internal structures of the forebrain
-They are the thalamostriate vein and
the choroidal vein. They drain the basal
ganglia, thalamus, internal capsule, choroid
plexus and hippocampus. -These
vessels merge to form the 2 internal
cerebral veins. -These 2 internal
cerebral veins unite in the midline to form the
great cerebral vein which lies beneath the
splenium of the corpus callosum - Thus
the great cerebral vein drains the deep
structures of the forebrain and the inferior
sagittal sinus. - It continuous with
the straight sinus which lies in the midline of
the tentorium cerebelli.
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3- Dural venous sinuses - The dural
venous sinuses are connected to
extracranial veins via emissary veins. -
Cerebral damage caused by venous
infarction manifests as epileptic attacks
and focal paralysis of the limbs.
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Disorders of Blood Supply of the Brain - The
sudden occlusion of the cerebral artery leads to
death of brain tissue (infarction
). Rupture of a blood vessel causes cerebral
haemorrhage. - Strokes related to the carotid
artery and its cerebral branches are associated
with focal epilepsy a contralateral sensory
motor deficit and a psychological deficit (
aphasia ). - Strokes involving the
vertebrobasillar circulation lead to a focal
brain stem syndrome. Recovery of function can
occur but take up to 2 years and can be
incomplete. - An aneurysm is an abnormal,
balloon-like, swelling of an artery. Rupture of
this artery may cause subarachnoid haemorrhage or
intracerebral haemorrhage. A sudden severe
headache and neck stiffness are followed by coma
and neurological deficits. - An angioma or
arteriovenous malformation is a congenital
collection of swollen, blood vessels that can
rupture causing cerebral haemorrhage or steal
blood from adjacent brain regions leading to
epilepsy and a focal cerebral syndrome.