THE BLOOD SUPPLY OF THE BRAIN
- Cerebrovascular accidents (CVA, stroke) still the third leading cause of
morbidity and death in the world.
- Consequently, it is important to know the areas of the cerebral cortex and
spinal cord supplied by a particular artery and to understand the
dysfunction that would result if the artery we re blocked.
Arteries of the Brain:
- The brain is supplied by the two inte rnal carotid and the two vertebral
arte ries.
- The four arte ries lie within the subarachnoid space, and their branches
anastomose on the inferior surface of the brain to form the circle of
Willis.
Inte rnal Carotid Arte ry:
- Begins at the bifurcation of the common carotid artery
- It ascends the neck and perforates the base of the skull by passing
through the carotid canal of the temporal bone.
- The artery then runs horizontally forward through the cavernous sinus
and emerges on the medial side of the anterior clinoid process by
perforating the dura mater.
- It now ente rs the subarachnoid space by piercing the arachnoid mater
and turns posteriorly to the region of the medial end of the lateral
cerebral sulcus.
- Here, it divides into the anterior and middle cerebral arteries
Branches of the Cerebral Portion:
1- The ophthalmic artery:
- Arises as the ICA emerges from the cavernous sinus
- Enters the orbit through the optic canal below and lateral to the optic
nerve.
- It supplies the eye and othe r orbital structures, and its terminal branches
supply the frontal area of the scalp, the ethmoid and frontal sinuses, and
the dorsum of the nose.
2- The posterior communicating artery:
- Is a small vessel that originates from the internal carotid artery close to
its terminal bifurcation
- Runs posteriorly above the oculomotor nerve to join the posterior
cerebral arte ry, thus forming part of the circle of Willis.
3- The choroidal arte ry:
- A small branch, also originates from the ICA close to its terminal
bifurcation.
- Passes posteriorly close to the optic tract, enters the infe rior horn of the
lateral ventricle, and ends in the choroid plexus.
4- The anterior cerebral arte ry:
- Is the smaller terminal branch of the inte rnal carotid arte ry
- It runs forward and medially superior to the optic ne rve and enters the
longitudinal fissure of the cerebrum, he re, it is joined to the anterior
cerebral arte ry of the opposite side by the ante rior communicating arte ry.
- It curves backward over the corpus callosum and, finally, anastomoses
with the posterior cerebral artery
- The cortical branches supply all the medial surface of the cerebral cortex
as far back as the parieto-occipital sulcus
- They also supply a strip of cortex about 1 inch (2.5 cm) wide on the
adjoining lateral s urface (the artery thus supplies the “leg area” of the
precentral gyrus).
- A group of central branches pierces the anterior pe rforated substance
and helps to supply parts of the lentiform and caudate nuclei and the
internal capsule.
5- The middle cerebral arte ry:
- The largest branch of the internal carotid, runs laterally in the late ral
cerebral sulcus
- Cortical branches supply the entire lateral surface of the hemisphere,
except for the narrow strip supplied by the ante rior cerebral arte ry, the
occipital pole, and the inferolateral surface of the hemisphere, which are
supplied by the posterior ce rebral artery
- This artery thus supplies all the motor area except the “leg area.”
- Central branches enter the anterior perforated substance and supply the
lentiform and caudate nuclei and the internal capsule
The basilar artery:
- Formed by the union of the two vertebral arteries
- Ascends in a groove on the anterior surface of the pons
- At the upper border of the pons, it divides into the two posterior cerebral
arte ries.
Branches
1- The pontine arteries: are nume rous small vessels that enter the substance of
the pons
2- The labyrinthine artery: is a long, narrow artery that accompanies the facial
and the vestibulocochlear nerves into the inte rnal acoustic meatus and supplies
the internal ear.
3- The anterior inferior cerebellar arte ry: passes posteriorly and laterally and
supplies the anterior and inferior parts of the cerebellum with few branches pass
to the pons and the upper part of the medulla.
4- The superior cerebellar artery: arises close to the termination of the basilar
arte ry It winds around the cerebral peduncle and supplies the superior surface
of the cerebellum, the pons, the pineal gland, and the superior medullary velum.
5- The posterior ce rebral artery:
- Curves laterally and backward around the midbrain and is joined by the
posterior communicating branch of the inte rnal carotid artery.
- Cortical branches supply the inferolateral and medial surfaces of the
temporal lobe and the lateral and medial surfaces of the occipital lobe.
Thus, the posterior ce rebral artery supplies the visual cortex.
- Central branches pierce the brain substance and supply parts of the
thalamus and the lentiform nucleus as well as the midbrain, the pineal,
and the medial geniculate bodies.
- A choroidal branch enters the inferior horn of the late ral ventricle and
supplies the choroid plexus; it also supplies the choroid plexus of the third
ventricle.
Circle of Willis:
- The circulus arte riosus (circle of Willis) lies in the inte rpeduncular fossa
at the base of the brain.
- It is formed by the anastomosis between the two internal carotid arteries
and the two vertebral arteries
- The anterior communicating, anterior cerebral, internal carotid,
posterior communicating, posterior ce rebral, and basilar arteries all
contribute to the circle.
- The circle of Willis allows blood that enters by eithe r internal carotid or
vertebral arteries to be distributed to any part of both cerebral
hemispheres.
- Cortical and central branches arise from the circle and supply the brain
substance.
- Variations in the sizes of the arteries forming the circle are common, and
the absence of one or both posterior communicating arteries has been
reported.
Arteries to Specific Brain Areas:
- The corpus striatum and the inte rnal capsule are supplied mainly by the
medial and lateral striate central branches of the middle cerebral arte ry,
the central branches of the anterior ce rebral artery supply the remainde r
of these structures.
- The thalamus is supplied mainly by branches of the posterior
communicating, basilar, and posterior cerebral arte ries.
- The midbrain is supplied by the posterior cerebral, superior cerebellar,
and basilar arte ries.
- The pons is supplied by the basilar and the anterior, infe rior, and
superior cerebellar arteries.
- The medulla oblongata is supplied by the vertebral, anterior and
posterior spinal, posterior inferior cerebellar, and basilar arteries.
- The cerebellum is supplied by the superior cerebellar, ante rior inferior
cerebellar, and posterior inferior cerebellar arteries.
Veins of the Brain:
- The veins of the brain have no muscular tissue in their very thin walls,
and they possess no valves.
- They emerge from the brain and lie in the subarachnoid space.
- They pierce the arachnoid mater and the meningeal layer of the dura and
drain into the cranial venous sinuses
External Cerebral Veins:
- The superior cerebral veins pass upward over the lateral surface of the
cerebral hemisphere and empty into the superior sagittal sinus
- The superficial middle cerebral vein drains the lateral surface of the
cerebral hemisphere. It runs infe riorly in the lateral sulcus and empties
into the cavernous sins
- The deep middle cerebral vein drains the insula and is joined by the
anterior cerebral and striate veins to form the basal vein .
- The basal vein ultimately joins the great cerebral vein, which in turn
drains into the straight sinus
Inte rnal Cerebral Veins
- There are two internal ce rebral veins, and they are formed by the union
of the thalamostriate vein and the choroid vein at the interventricular
foramen.
- The two veins run posteriorly in the tela choroidea of the third ventricle
and unite beneath the splenium of the corpus callosum to form the great
cerebral vein, which empties into the straight sinus.
- Cerebrovascular accidents (CVA, stroke) still the third leading cause of
morbidity and death in the world.
- Consequently, it is important to know the areas of the cerebral cortex and
spinal cord supplied by a particular artery and to understand the
dysfunction that would result if the artery we re blocked.
Arteries of the Brain:
- The brain is supplied by the two inte rnal carotid and the two vertebral
arte ries.
- The four arte ries lie within the subarachnoid space, and their branches
anastomose on the inferior surface of the brain to form the circle of
Willis.
Inte rnal Carotid Arte ry:
- Begins at the bifurcation of the common carotid artery
- It ascends the neck and perforates the base of the skull by passing
through the carotid canal of the temporal bone.
- The artery then runs horizontally forward through the cavernous sinus
and emerges on the medial side of the anterior clinoid process by
perforating the dura mater.
- It now ente rs the subarachnoid space by piercing the arachnoid mater
and turns posteriorly to the region of the medial end of the lateral
cerebral sulcus.
- Here, it divides into the anterior and middle cerebral arteries
Branches of the Cerebral Portion:
1- The ophthalmic artery:
- Arises as the ICA emerges from the cavernous sinus
- Enters the orbit through the optic canal below and lateral to the optic
nerve.
- It supplies the eye and othe r orbital structures, and its terminal branches
supply the frontal area of the scalp, the ethmoid and frontal sinuses, and
the dorsum of the nose.
2- The posterior communicating artery:
- Is a small vessel that originates from the internal carotid artery close to
its terminal bifurcation
- Runs posteriorly above the oculomotor nerve to join the posterior
cerebral arte ry, thus forming part of the circle of Willis.
3- The choroidal arte ry:
- A small branch, also originates from the ICA close to its terminal
bifurcation.
- Passes posteriorly close to the optic tract, enters the infe rior horn of the
lateral ventricle, and ends in the choroid plexus.
4- The anterior cerebral arte ry:
- Is the smaller terminal branch of the inte rnal carotid arte ry
- It runs forward and medially superior to the optic ne rve and enters the
longitudinal fissure of the cerebrum, he re, it is joined to the anterior
cerebral arte ry of the opposite side by the ante rior communicating arte ry.
- It curves backward over the corpus callosum and, finally, anastomoses
with the posterior cerebral artery
- The cortical branches supply all the medial surface of the cerebral cortex
as far back as the parieto-occipital sulcus
- They also supply a strip of cortex about 1 inch (2.5 cm) wide on the
adjoining lateral s urface (the artery thus supplies the “leg area” of the
precentral gyrus).
- A group of central branches pierces the anterior pe rforated substance
and helps to supply parts of the lentiform and caudate nuclei and the
internal capsule.
5- The middle cerebral arte ry:
- The largest branch of the internal carotid, runs laterally in the late ral
cerebral sulcus
- Cortical branches supply the entire lateral surface of the hemisphere,
except for the narrow strip supplied by the ante rior cerebral arte ry, the
occipital pole, and the inferolateral surface of the hemisphere, which are
supplied by the posterior ce rebral artery
- This artery thus supplies all the motor area except the “leg area.”
- Central branches enter the anterior perforated substance and supply the
lentiform and caudate nuclei and the internal capsule
The basilar artery:
- Formed by the union of the two vertebral arteries
- Ascends in a groove on the anterior surface of the pons
- At the upper border of the pons, it divides into the two posterior cerebral
arte ries.
Branches
1- The pontine arteries: are nume rous small vessels that enter the substance of
the pons
2- The labyrinthine artery: is a long, narrow artery that accompanies the facial
and the vestibulocochlear nerves into the inte rnal acoustic meatus and supplies
the internal ear.
3- The anterior inferior cerebellar arte ry: passes posteriorly and laterally and
supplies the anterior and inferior parts of the cerebellum with few branches pass
to the pons and the upper part of the medulla.
4- The superior cerebellar artery: arises close to the termination of the basilar
arte ry It winds around the cerebral peduncle and supplies the superior surface
of the cerebellum, the pons, the pineal gland, and the superior medullary velum.
5- The posterior ce rebral artery:
- Curves laterally and backward around the midbrain and is joined by the
posterior communicating branch of the inte rnal carotid artery.
- Cortical branches supply the inferolateral and medial surfaces of the
temporal lobe and the lateral and medial surfaces of the occipital lobe.
Thus, the posterior ce rebral artery supplies the visual cortex.
- Central branches pierce the brain substance and supply parts of the
thalamus and the lentiform nucleus as well as the midbrain, the pineal,
and the medial geniculate bodies.
- A choroidal branch enters the inferior horn of the late ral ventricle and
supplies the choroid plexus; it also supplies the choroid plexus of the third
ventricle.
Circle of Willis:
- The circulus arte riosus (circle of Willis) lies in the inte rpeduncular fossa
at the base of the brain.
- It is formed by the anastomosis between the two internal carotid arteries
and the two vertebral arteries
- The anterior communicating, anterior cerebral, internal carotid,
posterior communicating, posterior ce rebral, and basilar arteries all
contribute to the circle.
- The circle of Willis allows blood that enters by eithe r internal carotid or
vertebral arteries to be distributed to any part of both cerebral
hemispheres.
- Cortical and central branches arise from the circle and supply the brain
substance.
- Variations in the sizes of the arteries forming the circle are common, and
the absence of one or both posterior communicating arteries has been
reported.
Arteries to Specific Brain Areas:
- The corpus striatum and the inte rnal capsule are supplied mainly by the
medial and lateral striate central branches of the middle cerebral arte ry,
the central branches of the anterior ce rebral artery supply the remainde r
of these structures.
- The thalamus is supplied mainly by branches of the posterior
communicating, basilar, and posterior cerebral arte ries.
- The midbrain is supplied by the posterior cerebral, superior cerebellar,
and basilar arte ries.
- The pons is supplied by the basilar and the anterior, infe rior, and
superior cerebellar arteries.
- The medulla oblongata is supplied by the vertebral, anterior and
posterior spinal, posterior inferior cerebellar, and basilar arteries.
- The cerebellum is supplied by the superior cerebellar, ante rior inferior
cerebellar, and posterior inferior cerebellar arteries.
Veins of the Brain:
- The veins of the brain have no muscular tissue in their very thin walls,
and they possess no valves.
- They emerge from the brain and lie in the subarachnoid space.
- They pierce the arachnoid mater and the meningeal layer of the dura and
drain into the cranial venous sinuses
External Cerebral Veins:
- The superior cerebral veins pass upward over the lateral surface of the
cerebral hemisphere and empty into the superior sagittal sinus
- The superficial middle cerebral vein drains the lateral surface of the
cerebral hemisphere. It runs infe riorly in the lateral sulcus and empties
into the cavernous sins
- The deep middle cerebral vein drains the insula and is joined by the
anterior cerebral and striate veins to form the basal vein .
- The basal vein ultimately joins the great cerebral vein, which in turn
drains into the straight sinus
Inte rnal Cerebral Veins
- There are two internal ce rebral veins, and they are formed by the union
of the thalamostriate vein and the choroid vein at the interventricular
foramen.
- The two veins run posteriorly in the tela choroidea of the third ventricle
and unite beneath the splenium of the corpus callosum to form the great
cerebral vein, which empties into the straight sinus.
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