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.
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.
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.
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.
Branches of Basilar Artery:
1. Pontine arteries
2. 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.
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.
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.
Venous Drainage of the Brain
1- Superficial veins:
They lie within the subarachnoid space.
a. Superior cerebral veins
They drain the lateral surface of the cerebral
hemispheres and empty into the superior
sagittal sinus.
C
A
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.
B
d. Inferior anastomotic vein
It drains into the transverse sinus.
N.B. The circular sinus is a venous circle
around the hypophysis.
D
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.
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.
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.