The Blood Supply of the Brain and Spinal Cord Dr. Nimir Dr. Safaa.
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The Blood Supply of the Brain and Spinal Cord
Dr. NimirDr. Safaa
• Objectives
• Describe the four arteries supplying the CNS. • Follow up each artery to its destination. • Describe the circle of Willis and its branches. • Discuss the principle of end artery type of
circulation. • Describe venous drainage of the brain.
Blood Supply of the Brain• The brain is supplied by:• Two internal carotid arteries• Two vertebral arteries. • They lie within subarachnoid space• Their branches anastomose on inferior surface of brain to form Circle
of Willis.
Internal Carotid Artery• It begins at the bifurcation of
the common carotid artery, where it has the carotid sinus.
• It ascends by passing through the carotid canal of the temporal bone.
• Then pass through cavernous sinus and perforates the dura mater and enters the subarachnoid space .
• At the medial end of the lateral cerebral sulcus it divides into :
• Anterior cerebral artery• Middle cerebral artery
Branches of internal carotid artery
Ophthalmic artery supplies:
• The eye • Frontal area of scalp• Ethmoid and frontal
sinuses• Dorsum of nose. Posterior
communicating artery join the posterior cerebral artery, forming part of circle of Willis.
Choroidal artery• Enters inferior
horn of lateral ventricle to form choroid plexus.
• It gives branches to:
• Crus cerebri• Lateral
geniculate body• Optic tract• Internal capsule.
Anterior cerebral artery• It enters longitudinal
fissure of the cerebrum where it joins artery of opposite side by anterior communicating artery.
Cortical branches supply:• All the medial surface of
the cerebrum till parieto-occipital sulcus
• 1 inch of lateral surface (leg area).
Central branches supply: • Parts of lentiform• Caudate nuclei • Internal capsule.
Middle cerebral artery • It is largest branch of
internal carotid, runs in lateral cerebral sulcus.
Its cortical branches supply:• Entire lateral & orbital
surfaces of cortex • Except:• 1 inch of lateral supplied by
anterior cerebral artery• Occipital pole and
inferolateral surface of hemisphere supplied by posterior cerebral artery
• Thus supplies all body except the (leg area).
Central branches enter the anterior perforated substance and supply the:
• Lentiform and caudate nuclei • Internal capsule
Vertebral Artery:• Branch of the first part
of subclavian artery• Passes through
foramina transverseria of the upper six cervical vertebrae
• Enters skull through foramen magnum.
• At the lower border of the pons, it joins the vessel of the opposite side to form the basilar artery.
• Branches of vertebral artery:
• Meningeal branches supply bone and dura in posterior cranial fossa.
• Posterior spinal artery. • Anterior spinal artery.• Posterior inferior cerebellar
artery largest branch of vertebral which supplies:
• Cerebellum• Medulla oblongata • Choroid plexus of fourth
ventricle.• Medullary arteries to
medulla oblongata.
Basilar Artery• It is formed by union of
the two vertebral arteries at the pons.
• Its branches are:• Pontine arteries to pons.• Labyrinthine artery to
internal ear.• Anterior inferior cerebellar
artery(AICA) for cerebellum,pons & upper medulla.
• Superior cerebellar artery for cerebellum,pons & pineal gland.
• Posterior cerebral artery is joined by posterior communicating branch of internal carotid.
Its cortical branches supply:
• Inferolateral & medial surfaces of temporal lobe
• lateral & medial surfaces of occipital lobe (visual cortex).
Its central branches supply:
Thalamus Lentiform nucleus Midbrain Pineal gland Medial geniculate
bodies. Choroidal branch for
choroid plexus of lateral & third ventricles.
• Circle of Willis:• It lies in the
interpeduncular fossa at the base of the brain.
• It is formed by the anastomosis between the two internal carotid arteries and the two vertebral arteries.
• It allows blood that enters by either internal carotid or vertebral arteries to be distributed to any part of both cerebral hemispheres.
• Arteries to specific brain areas:
• Corpus striatum and internal capsule supplied mainly by medial and lateral striate central branches of middle cerebral artery plus central branches of anterior cerebral artery.
• Thalamus is supplied mainly by posterior communicating, basilar, and posterior cerebral arteries.
• Midbrain is supplied by posterior cerebral, superior cerebellar, and basilar arteries.
• Pons is supplied by basilar and anterior, inferior, and superior cerebellar arteries.
• Medulla oblongata is supplied by vertebral, anterior and posterior spinal, posterior inferior cerebellar, and basilar arteries.
• Cerebellum is supplied by superior cerebellar, anterior inferior cerebellar, and posterior inferior cerebellar arteries.
• End arteries (terminal):• Anatomic (True) End
Artery: No anastomoses.• Functional End Artery:
Ineffectual anastomoses.• An example of a true
terminal arteries is that which supplies the retina.
• Functional end arteries supply segments of the brain.
Veins of the Brain• They have no muscular tissue in their walls, and they have no valves.
They lie in subarachnoid space. They drain into the cranial (dural) venous sinuses.
• Emissary veins connect the dural venous sinuses with the diploic veins of the skull and with the veins of the scalp
• Cerebral veins divided into:
External Cerebral Veins:• Superior cerebral veins
drains superolateral & medial surfaces and empty into the superior sagittal sinus.
• Superficial middle cerebral vein drains the lateral surface of the cerebral hemisphere & empties into the cavernous sinus.
• Deep middle cerebral vein drains insula and is joined by anterior cerebral and striate veins to form the basal vein.
• Basal vein joins the great cerebral vein, which in turn drains into straight sinus .
Internal Cerebral Veins• There are two internal
cerebral veins.• They are formed by union
of the thalamostriate vein and choroid vein
• The two unite to form the great cerebral vein, which is joined with basal veins & empties into the straight sinus.
Veins of specific brain areas:• Midbrain is drained by
veins that open into the basal or great cerebral veins.
• Pons is drained by veins that open into basal vein, cerebellar veins.
• Medulla oblongata is drained by veins that open into spinal veins.
• Cerebellum is drained by veins that empty into great cerebral vein or adjacent venous sinuses.
Dural venous sinuses• The dural venous sinuses are endothelial-lined spaces
between the outer periosteal and the inner meningeal layers of the dura mater
• They finally drain into internal jugular veins• Emptying into the dural venous sinuses are diploic vein and
emissary veins.
The dural venous sinuses • Superior sagittal sinus• Inferior sagittal sinus• Straight sinus• Transverse sinuses• Sigmoid sinuses• Occipital sinuses• Confluence of sinuses• Superior petrosal• Inferior petrosal• Cavernous sinuses
The superior sagittal sinus• Deviates ,usually the right
& becomes continuous with the right transverse sinus.
• It communicates with venous lacunae on each side.
• Numerous arachnoid villi and granulations project into the lacunae
• It usually becomes continuous with the right transverse sinus.
• At the internal occipital protuberance, it is dilated to form the confluence of the sinuses
• It receives :• The superior cerebral
veins• The occipital sinus • Diploic & emissary veins • CSF(through arachnoid
granulations)
The inferior sagittal sinus
• Joins the great cerebral vein to form the straight sinus
• It receives a few cerebral veins from the medial surface of the cerebral hemispheres.
The straight sinus • Is formed by the union of
the inferior sagittal sinus with the great cerebral vein.
• It ends by turning to the left (sometimes to the right) to form the transverse sinus.
• It receives:• Inferior sagittal sinus• Great cerebral vein,
posterior cerebral veins• Superior cerebellar veins• Veins from the falx cerebri
• The transverse sinuses • Are paired structures that
begins at the internal occipital protuberance
• The right sinus is usually continuous with the superior sagittal sinus, and the left is continuous with the straight sinus.
• The transverse sinuses receive the:
• Superior petrosal sinuses• Inferior cerebral • Cerebellar veins• Diploic veins. • They end by turning downward
as the sigmoid sinuses .
• The sigmoid sinuses • Are a direct continuation of
the transverse sinuses.• The sinus then reaches the
posterior part of the jugular foramen to become continuous with the superior bulb of the internal jugular vein.
• The occipital sinus • Is a small sinus occupying the
attached margin of the falx cerebelli.
• It communicates with the internal vertebral venous plexus
• Drains into the confluence of sinuses.
The cavernous sinuses • Are situated in the
middle cranial fossa on each side of the body of the sphenoid bone
• The two sinuses communicate with each other by anterior and posterior intercavernous sinuses cerebri .
• The cavernous sinus receives:• Cerebral and ophthalmic veins• Emissary veins from pterygoid plexus of veins • Sphenoparietal sinuses• It has important communication with the facial vein through the
superior ophthalmic vein. (This is a route by which infection can travel from the facial skin to the cavernous sinus.)
Structures passing through each cavernous sinus are:
• The internal carotid artery;
• The abducent nerve [VI].
Structures in the lateral wall of cavernous sinus are the :
• Oculomotor nerve [III]; • Trochlear nerve [IV]; • Ophthalmic nerve [V1];
• Maxillary nerve [V2].
• The superior and inferior petrosal sinuses
• Are small sinuses situated on the superior and inferior borders of the petrous part of the temporal bone .
• Superior sinuses drain the cavernous sinus into the transverse sinus.
• Inferior sinuses drains the cavernous sinus into the internal jugular vein.
Blood Supply of the Spinal Cord
• It is supplied by three arteries:
• Two posterior spinal arteries from vertebral arteries.
• Anterior spinal artery from union of two arteries from vertebral artery .
• Spinal arteries are reinforced by segmental arteries that arise from arteries outside the vertebral column.
• Each segmental spinal artery gives rise to anterior and posterior radicular arteries
• The great anterior medullary artery of Adamkiewicz , that arise from the aorta, enters the vertebral canal and anastomoses with the anterior and posterior spinal arteries.
Veins of the Spinal Cord• The veins of the spinal cord drain into six
tortuous longitudinal channels that communicate within the skull with the veins of the brain and the venous sinuses.
• They drain mainly into the internal vertebral venous plexus.
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