Blood supply of the Brain

1. BLOOD SUPPLY OF THE BRAIN
DR AKEEM
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2. INTRODUCTION
• The blood supply of the CNS is of special interest because of the metabolic
demands of the nervous tissue
• The brain depends on aerobic metabolism of glucose and its one of the most
metabolically active organs of the body
• About 18% of the total blood volume in the body circulates in the brain, which
accounts for about 2% of the body weight, and consumes about 25% of the total
body Oxygen
• The blood transports oxygen, nutrients, and other substances necessary for proper
functioning of the brain tissues and carries away metabolites.
• Loss of consciousness occurs in less than 15 seconds after blood flow to the brain
has stopped, and irreparable damage to the brain tissue occurs within 5 minutes.
• This is responsible for more neurological disorders than any other category of
disease process. 2

3. 3

4. Arterial Supply to the Brain
• The brain is supply by four
major arteries.
A. Two internal carotid
arteries.
B. Two vertebral arteries.
• They will lie eventually
within the subarachnoid
space.
• Their branches anastomose
on the inferior of the brain to
form Arterial Circle Of
Willis.
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5. Internal Carotid Arteries
• Begins at the bifurcation of the common
carotid artery at level of c3 to c4
intervertebral disc.
• Possess a localised dilatation called carotid
sinus at origin.
• Transverses the carotid canal at the base of the
skull and enters the middle cranial fossa beside
the dorsum sallae of the sphenoid bone.
• Runs horizontally forward in the cavernous
sinus and then perforate the dura mater.
• Enters the subarachnoid process by perforating
the arachnoid mater.
• It divides here into Middle And Anterior
Cerebral Arteries.
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6. Branches of the ICA
• The ophthalmic
artery
• The posterior
communicating
artery
• The anterior
choroidal artery
• The anterior
cerebral artery
• The middle
cerebral artery
• The hypophyseal
arteries
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7. Ophthalmic artery: This branch comes off immediately after the internal carotid
artery enter the sub arachnoid space.
• 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.
Anterior Choroidal artery: This artery comes out of the distal part of the internal
carotid or the beginning of the middle cerebral artery.
• The artery passes back along the optic tract and the choroid fissure at the medial
edge of the temporal lobe.
• It supplies the optic tract, choroid plexus in the temporal horn of the lateral
ventricle, hippocampus and uncus, amygdala, lateral geniculate nucleus, including
the ventral part of the internal capsule and globus pallidus.
• The branching is variable and sometimes supplies the subthalamus, ventral parts
of the thalamus and rostral parts of the midbrain (including the red nucleus).
• The terminal branches supplies the choroid plexus in the temporal horn of the
lateral ventricle and anastomose there with the branches of the posterior choroidal
arteries.
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8. Occlusion of the Internal Carotid
As a result of the occlusion of the middle and anterior cerebra occlusion the
ophthalmic and anterior choroidal occlusion can lead to:
• Principally, a contralateral hemiplegia and hemianopsia, with global aphasia if the
affected hemisphere is dominant for language.
• Blindness of the ipsilateral eye supplied by the ophthalmic artery
• Blindness of the contralateral half of the visual field of the other eye; from the
infarction of the optic tract and lateral geniculate body, supplied by the anterior
choroidal artery.
Occlusion of the anterior choroidal artery alone can be asymptomatic or varieties
of effect depending on the site obstruction and the efficiency of its anastomoses
with the posterior choroidal artery, symptoms can include;
• Contralateral hemiplegia and sensory abnormalities (Internal capsule)
• Contralateral homonymous hemianopsia (optic tract and lateral geniculate body)
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9. Anterior cerebral artery: the smaller terminal branch of the internal carotid, which is
first directly medially above the optic nerve.
• The two anterior cerebral arteries almost meet at the midline where they are joined
together by the anterior communicating artery.
• A special branch is given off just proximal to the anterior communicating artery
called the recurrent artery of Heubner or the medial striate artery; penetrates
the anterior perforated substance to supply the ventral part of the head of caudate
nucleus, adjacent portion of the putamen, anterior limb and genu of the internal
capsule. It also supplies the corpus striatum.
• It follows the curvature of corpus callosum within the great longitudinal fissure,
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.
Posterior communicating artery: this slender artery arise from the internal carotid
close to its terminal bifurcation.
• It passes backwards to join the posterior cerebral artery. It give rise to some
posteromedial central arteries.
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10. Occlusion of the Anterior Cerebral Artery
• It causes paralysis and sensory deficits in the contralateral leg and perineum
• Obstruction of the proximal part of the vessel blocking the recurrent artery of
Heubner, there is contralateral upper motor neuron weakness of the face, tongue and
upper limb because of the corticofugal motor fibres in or close to the genu of the
internal capsule before they pass into the posterior limb.
• Proximal occlusion may also cause ipsilateral anosmia due to infarction of the
olfactory bulb and tract.
• Anterior cerebral artery syndrome are often associated with mental confusion and
dysphasia, but attributable to loss of functions of the prefrontal cortex, the cingulate
gyrus, and supplementary motor area.
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11. Middle cerebral artery: It is the largest branch of the 3 cerebral arteries and its cortical
territory is the largest and a more direct continuation of the internal carotid.
• It runs deep in the lateral sulcus between the frontal and temporal lobes.
• The proximal part give rise to the anteromedial group of central arteries lateral to the
optic chiasma, they enter the bas of the hemisphere to supply internal structures such
as the internal capsule.
• Its corresponding branches which emerge from the lateral sulcus 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 most of the primary motor and premotor cortex, frontal eye fields and
primary somatosensory area (i.e. The motor and sensory cortices for the whole body
excluding the lower limb and perineum).
• The left middle cerebral artery (in most people) supplies all cortical areas concerned
with language.
Hypophyseal Artery: originates from the cavernous and post-clinoid portions of the
internal carotid artery.
• Post. Hypophyseal artery supply the neural lobe of the pituitary gland while the Ant.
Hypophyseal artery enters the median eminence of the hypothalamus.
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12. Occlusion of the Middle Cerebra Artery
• It can lead to loss of function of the cortical areas, which result in contralateral
paralysis most noticeable in the lower part of the face and in the arm, together with
general sensory deficit of the cortical type.
• Involvement of the geniculo-calcarine tracts results in hemianopsia of the
contralateral visual fields of both eyes.
• Unilateral lesion in the auditory cortex does not impair hearing because of the
bilateral projection from the Organ of Corti
• Occlusion in the dominant hemisphere for language causes global aphasia
• Fragments of complete syndrome such as monoplegia and receptive aphasia when
individual cortical branches are blocked.
• Obstruction of the central branches can cause hemiplegia due to infarction of the
motor fibres in the internal capsule.
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15. Vertebrobasilar System
• The vertebra artery is a branch of the
subclavian artery and ascend in the
foramina of the transverse processes
of the upper 6 cervical vertebrae
• On reaching the base of the skull, it
winds around the lateral mass of the
atlas, pierces the posterior atlanto-
occipital membrane, Enters the
subarachnoid space at the level of the
Foramen magnum by piercing the
dura and arachnoid mater..
• The vertebra artery runs forward with
the medial inclination beneath the
medulla, joining its fellow of the
opposite side at the caudal border of
the pons to form the basilar artery.
• The basilar artery runs rostrally in the
midline of the pons and divides into the
posterior cerebral arteries.

16. Branches of the Vertebral Artery
• Spinal Arteries: the upper portion of the
cervical cord receives blood through the
spinal branches of the vertebral arteries. A
single anterior spinal artery is formed
from each vertebra artery. A posterior
spinal artery arises on each side as a
branch of either the vertebral or posterior
inferior cerebellar artery. The anterior and
posterior spinal arteries continued through
out the length of the spinal cord
• Posterior inferior cerebellar artery
(PICA): largest branch of the vertebra
artery; it pursues an irregular curse
between the cerebellum and the medulla.
Branches are distributed to the posterior
part of the cerebellar hemisphere, inferior
vermis, central nuclei of the cerebellum
and choroid plexus of the 4th ventricle. Also
are important medullary branches to the
dorsolateral region of the medulla. In
addition fine branches arises directly from
the vertebral arteries to supply the medulla.
• Meningeal branches: small and supply the
bone and dura in the posterior cranial fossa.
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17. Basilar artery
• Formed by the union of the two vertebral arteries.
• Ascends in a groove on the anterior surface of the pons.
• At a point called the ponto-mesencephalic junction, it divides into the two pairs of posterior cerebral
arteries.
• At the point close to the terminal bifurcation of the basilar artery of pons and midbrain it gives off two
pairs of vessels, the superior cerebellar arteries
• N.B. The brain stem, cerebellum and occipital lobe are supplied by the vertebra-basilar system.
Branches :
• Anterior inferior cerebellar
artery (AICA):
• Labyrinthine artery
• Pontine arteries
• Superior cerebellar arteries:
• Posterior cerebral arteries
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18. • Anterior inferior cerebellar artery (AICA): arising from the caudal end of the
basilar, supplies the cortex of the inferior surface of the cerebellum anteriorly and
the underlying white matter, assist in the supply of central cerebellar nuclei, also
some slender twigs penetrate the upper medulla and lower pons
• The labyrinthine artery: is a branch or either the basilar artery or the AICA, long,
narrow artery that accompanies the facial and the vestibulocochlear nerves into the
internal acoustic meatus and ramifies throughout the membranous labyrinth of the
internal ear.
• Pontine arteries: slender arteries that arise along the length of the basilar artery.
They penetrate the pons and ramify in both the pons and the pontine tegmentum.
• Superior cerebellar artery: arise close to the terminal bifurcation of the basilar
artery, ramifies over the dorsal surface of the cerebellum, and supplies the cortex,
medullary centre, central nuclei. Branches from the proximal part are distributed to
the pons, superior cerebellar peduncle and inferior colliculus of the midbrain.
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19. Posterior cerebral arteries
• The main terminal branches of the basilar artery.
• curves laterally and backward around the midbrain.
• It is join by the posterior communicating artery.
Branches
• Cortical branches: Temporal, calcarine and parieto-
occipital branches.
It supplies the visual cortex:
• inferolateral and medial part of temporal lobe, supplies
much of the parahippocampus gyri and parts of the
hippocampus
• Lateral and medial aspect of occipital lobe; supplies the
primary visual associated cortex for vision
• Central branches: pierce the brain substance and supply
parts of the thalamus and the lentiform nucleus, midbrain,
the pineal, and the medial geniculate bodies.
• A posterior choroidal branch : Enters the inferior horn of
the lateral ventricle and supplies the choroid plexus of the
central part of the lateral ventricles; it also supplies the
choroid plexus of the third ventricle, posterior part of the
thalamus, fornix, the tectum of the midbrain. Its terminal
branches anastomose with those of the anterior choroidal
artery, within the choroid plexus of the lateral ventricles 19

20. Cerebral Arterial Circle
• An important anastomoses at the
base of the brain.
• Formed by the several arteries that
supply the brain.
• Located in the inter-peduncular
fossa in the base of the brain.
• Allows blood from either vessels to
be distributed to any part of both
cerebral hemispheres.
Contributing arteries include:
• Anterior communicating artery.
• Anterior cerebral arteries. (Right and
left)
• Internal carotid arteries (Right and left)
• Posterior communicating arteries (Right
and left)
• Posterior cerebral arteries (Right and
left)
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23. Cerebral arteries
• Anterior cerebral artery:
medial and superior surface of
the brain and frontal lobe.
• Middle cerebral artery: lateral
surface of the brain and temporal
lobe.
• Posterior cerebral artery:
inferior surface of the brain and
occipital lobe.
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25. Arteries to specific brain areas
• Pons: Basilar and the anterior, inferior, and superior cerebellar arteries.
• Thalamus: Posterior communicating, basilar, and posterior cerebral arteries.
• Cerebellum: Superior cerebellar, anterior inferior cerebellar, and posterior
inferior cerebellar arteries.
• Medulla oblongata: Superior cerebellar, anterior inferior cerebellar, and
posterior inferior cerebellar arteries.
• Corpus striatum and the internal capsule: the middle cerebral artery
• Midbrain: Posterior cerebral, superior cerebellar, and basilar arteries
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27. SUMMARY OF BLOOD SUPPLY TO THE BRAIN
• The brain receives blood from two sources: the internal carotid arteries,
which arise at the point in the neck where the common carotid arteries
bifurcate, and the vertebral arteries.
• The internal carotid arteries branch to form two major cerebral arteries, the
anterior and middle cerebral arteries.
• The right and left vertebral arteries come together at the level of the pons on
the ventral surface of the brainstem to form the midline basilar artery.
• The basilar artery joins the blood supply from the internal carotids in an
arterial ring at the base of the brain (in the vicinity of the hypothalamus and
cerebral peduncles) called the circle of Willis.
• The posterior cerebral arteries arise at this confluence, as do two small
bridging arteries, the anterior and posterior communicating arteries.
• Conjoining the two major sources of cerebral vascular supply via the circle
of Willis presumably improves the chances of any region of the brain
continuing to receive blood if one of the major arteries becomes occluded
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28. Venous drainage of the brain
• The veins of the brain have
no muscular tissue in their
very thin walls.
• they possess no valves.
• They emerge from the brain
and lie in the subarachnoid
space.
• Drain into the cranial
venous sinuses.
• They are grouped into
superficial and deep venous
system.
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29. Superficial venous system
• Superior cerebral veins
(superior lateral surface of
the brain: Drain the lateral
and medial surface of the
hemisphere and empty into
superior sagittal sinus.
• Middle cerebral veins: Drain
the inferolateral surface of the
hemisphere, and open into the
cavernous sinus
• Inferior cerebral veins: drain
the inferior surface of the
hemisphere and open into the
cavernous and transverse
sinuses.
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30. Deep venous system
Many but all communicate to form two
main tributaries:
(a) Internal cerebral vein: formed by
thalamostriate vein and septal vein.
(b) Basal vein: from medial part of
anterior temporal lobe and empty
into great cerebral vein.
GREAT CEREBRAL VEIN: from
internal and basal vein and joins the
inferior sagittal sinus and forms the
straight sinus.
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32. Nerve supply of the cerebral arteries
• Majorly innervated by the sympathetic postganglionic nerve fibres.
• The fibres are derived from the superior cervical sympathetic ganglion.
• Stimulation of this nerve leads to vasoconstriction.
• However, under normal conditions, the local blood flow is mainly controlled by the
concentrations of carbon dioxide, hydrogen ions, and oxygen present in the nervous
tissue;
• A rise in the carbon dioxide and hydrogen ion concentrations and a lowering of the
oxygen tension bring about a vasodilatation.
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33. Cerebrovascular Disease
• Arterial occlusion by an embolus or a thrombus usually is followed by infarction of
a portion of the region supplied.
• In addition to intracranial occlusion, impairment of cerebral circulation often is the
result of stenosis of a carotid or vertebral artery in the neck.
• Cerebral haemorrhage is majorly caused by the hypertension and degenerative
changes in some slender thin walled arteries that penetrates the ventral surface of the
brain to supply the internal capsule and some adjacent grey matter, because they are
prone to rupture.
• An aneurysm of larger arteries can occur at the base of the brain; it may rupture or
leak causing bleeding into the subarachnoid space and in turn lead to intra cerebral
haemorrhage or cranial nerve haemorrhage.
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34. Clinical Anatomy
• Cerebral arterial
circle variation.
• Stroke
• Brain infarction:
Atherosclerotic
plaque
• Transient ischaemic
attack.
Variation comes in:
• Inadequate anastomoses frequently
becomes inadequate especially in
elderly people with narrowed
communicating arteries as a result of
vascular disease.
• Size of arterial vessels.
• Absence of posterior communicating
artery.
• Presence of two anterior communicating
arteries.
• 1 in 3 people has posterior cerebral
artery as a major branch of internal
carotid artery.
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35. Clinical Anatomy
• Stroke: Sudden development
of focal neurological deficits
that are usually related to
impaired cerebral blood flow.
Cause:
Spontaneous cerebrovascular
accidents such as cerebral
thrombosis, cerebral hemorrhage,
cerebral embolism, and
subarachnoid hemorrhage
Types:
(1) Haemorrhagic stroke.
(2) Ischemic stroke.
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36. • Brain infarction: Atherosclerotic
plaque
This event usually results in acute
cortical infarction, a sudden
insufficiency of arterial blood to the
brain (e.g., of the left parietal lobes).
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37. Clinical Anatomy
• Stroke is the most common neurological cause for admission to a hospital, and is the third
leading cause of death in the United States (after heart disease and cancer). The term “stroke”
refers to the sudden appearance of a limited neurological deficit, such as weakness or
paralysis of a limb, or the sudden inability to speak. The onset of the deficit within seconds,
minutes, or hours marks the problem a vascular one. Brain function is exquisitely dependent
on a continuous supply of oxygen, as evidenced by the onset of unconsciousness within about
10 seconds of blocking its blood supply (by cardiac arrest, for instance). The damage to
neurons is at first reversible, but eventually becomes permanent if the blood supply is not
promptly restored.
• Strokes can be subdivided into three main types: thrombotic, embolic, and hemorrhagic. The
thrombotic variety is caused by a local reduction of blood flow arising from an atherosclerotic
buildup in one of the cerebral blood vessels that eventually occludes it. Alternatively, a
reduction of blood flow can arise when an embolus (meaning an object loose in the
bloodstream) dislodges from the heart (or from an atherosclerotic plaque in the carotid or
vertebral arteries) and travels to a cerebral artery (or arteriole) where it forms a plug. A
hemorrhagic stroke occurs when a cerebral blood vessel ruptures, as can occur as a result of
hypertension, a congenital aneurysm (bulging of a vessel), or a congenital arterio-venous
malformation. The relative frequency of thrombotic, embolic, and hemorrhagic strokes is
approximately 50%, 30%, and 20%, respectively.
• The diagnosis of stroke relies primarily on an accurate history and a competent neurological
examination. Indeed, the neurologist C. Miller Fisher, a master of bedside diagnosis,
remarked that medical students and residents should learn neurology “stroke by stroke.”
Understanding the portion of the brain supplied by each of the major arteries (see text)
enables an astute clinician to identify the occluded blood vessel.
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