Study sheet: Blood Supply of the Brain and Spinal Cord

📋 Course Outline

1. Arterial Sources and Circle of Willis
2. Internal Carotid Artery Course
3. Internal Carotid Branches
4. Vertebral and Basilar Arteries
5. Cerebellar and Cerebral Branches
6. Territorial Brain Arterial Supply
7. Cerebral Venous Drainage
8. Spinal Cord Vascular Supply

📖 1. Arterial Sources and Circle of Willis

🔑 Key Concepts & Definitions

• Circle of Willis : an arterial anastomotic ring located in the interpeduncular fossa at the base of the brain

★ Must-know

• The brain is supplied by two internal carotid arteries and two vertebral arteries, whose branches anastomose on the inferior surface of the brain to form the circle of Willis.

• The circle of Willis includes:

  • the anterior communicating arteries
  • the anterior cerebral arteries
  • the internal carotid arteries
  • the posterior communicating arteries
  • the posterior cerebral arteries
  • the basilar artery

📌 The circle of Willis allows blood entering through either the internal carotid or vertebral arteries to reach either cerebral hemisphere, while cortical and central branches supply the brain substance.

Further detail

• Variations in the sizes of the arteries forming the circle of Willis are common, and one or both posterior communicating arteries may be absent.

💡 Memory Hook

Four arterial pillars meet in a ring beneath the brain.

📖 2. Internal Carotid Artery Course

🔑 Key Concepts & Definitions

• Carotid sinus : a localized dilatation usually present at the origin of the internal carotid artery at the common carotid bifurcation

★ Must-know

• 🔄 The internal carotid artery follows this course: begins at the common carotid bifurcation, ascends through the neck, passes through the carotid canal, runs through the cavernous sinus, pierces the dura and arachnoid, divides into the anterior and middle cerebral arteries

Further detail

• The internal carotid artery emerges from the cavernous sinus on the medial side of the anterior clinoid process before entering the subarachnoid space.

💡 Memory Hook

Bifurcation → carotid canal → cavernous sinus → subarachnoid space → cerebral branches

📖 3. Internal Carotid Branches

★ Must-know

• The ophthalmic artery arises as the internal carotid artery emerges from the cavernous sinus and enters the orbit through the optic canal below and lateral to the optic nerve.

• 🔄 The posterior communicating artery: arises near the internal carotid terminal bifurcation, runs posteriorly above the oculomotor nerve, joins the posterior cerebral artery

• The anterior cerebral artery is the smaller terminal branch of the internal carotid artery and supplies the medial cerebral cortex, including the leg area of the precentral gyrus.

• The middle cerebral artery is the largest branch of the internal carotid artery and supplies the lateral surface of the cerebral hemisphere and most of the motor area.

Further detail

• The choroidal artery supplies:
  • the choroid plexus
  • the crus cerebri
  • the lateral geniculate body
  • the optic tract
  • the internal capsule

📖 4. Vertebral and Basilar Arteries

★ Must-know

• 🔄 The vertebral artery follows this course: arises from the first part of the subclavian artery, passes through the transverse foramina of the upper six cervical vertebrae, enters the skull through the foramen magnum, enters the subarachnoid space, joins the opposite vertebral artery at the lower border of the pons

• The posterior inferior cerebellar artery is the largest branch of the vertebral artery and supplies the inferior cerebellum, medulla oblongata, and choroid plexus of the fourth ventricle.

• The basilar artery ascends in a groove on the anterior pons and divides at the upper border of the pons into the two posterior cerebral arteries.

Further detail

• The anterior spinal artery is formed by a contributory branch from each vertebral artery and descends on the anterior surface of the medulla and spinal cord.

💡 Memory Hook

Vertebral arteries → basilar artery → posterior cerebral arteries

📖 5. Cerebellar and Cerebral Branches

★ Must-know

• The posterior cerebral artery supplies the inferolateral and medial temporal lobe, the lateral and medial occipital lobe, and therefore the visual cortex.

Further detail

• The labyrinthine artery accompanies the facial and vestibulocochlear nerves through the internal acoustic meatus to supply the internal ear and often arises from the anterior inferior cerebellar artery.

• The anterior inferior cerebellar artery supplies the anterior and inferior parts of the cerebellum and gives branches to the pons and upper medulla oblongata.

• The superior cerebellar artery supplies:

  • the superior surface of the cerebellum
  • the pons
  • the pineal gland
  • the superior medullary velum

• The posterior cerebral artery gives central branches to parts of the thalamus, lentiform nucleus, midbrain, pineal gland, and medial geniculate bodies, and a choroidal branch to the choroid plexuses of the lateral and third ventricles.

📖 6. Territorial Brain Arterial Supply

★ Must-know

• The corpus striatum and internal capsule are supplied mainly by the medial and lateral striate branches of the middle cerebral artery, with the remaining supply coming from central branches of the anterior cerebral artery.

• The thalamus is supplied mainly by branches of the posterior communicating, basilar, and posterior cerebral arteries.

• The cerebellum is supplied by:

  • the superior cerebellar arteries
  • the anterior inferior cerebellar arteries
  • the posterior inferior cerebellar arteries

Further detail

• The midbrain is supplied by the posterior cerebral, superior cerebellar, and basilar arteries, while the pons is supplied by the basilar and anterior, inferior, and superior cerebellar arteries.

• The medulla oblongata is supplied by:

  • the vertebral arteries
  • the anterior spinal arteries
  • the posterior spinal arteries
  • the posterior inferior cerebellar arteries
  • the basilar arteries

💡 Memory Hook

Anterior cerebral artery supplies the leg area, whereas middle cerebral artery supplies most of the lateral motor cortex.

📖 7. Cerebral Venous Drainage

★ Must-know

• Cerebral veins have very thin walls without muscular tissue or valves, emerge from the brain into the subarachnoid space, and drain through the arachnoid and meningeal dura into cranial venous sinuses.

• The superior cerebral veins drain the lateral cerebral hemisphere into the superior sagittal sinus, while the superficial middle cerebral vein drains the lateral surface into the cavernous sinus.

• The internal cerebral veins are formed by union of the thalamostriate and choroid veins at the interventricular foramen, run posteriorly in the tela choroidea, and unite beneath the splenium to form the great cerebral vein.

Further detail

• 🔄 Deep cerebral venous drainage proceeds through:

  1. the deep middle cerebral vein
  2. the anterior cerebral and striate veins
  3. the basal vein
  4. the great cerebral vein
  5. the straight sinus

• The midbrain drains into the basal or great cerebral veins, the pons drains into the basal vein, cerebellar veins, or neighboring sinuses, the medulla drains into spinal veins and neighboring sinuses, and the cerebellum drains into the great cerebral vein or adjacent sinuses.

💡 Memory Hook

Brain veins → subarachnoid space → dura → cranial venous sinuses

📖 8. Spinal Cord Vascular Supply

★ Must-know

📌 Posterior spinal arteries arise from the vertebral or posterior inferior cerebellar arteries and supply the posterior third of the spinal cord, whereas the anterior spinal artery supplies the anterior two-thirds.

• Segmental spinal arteries arise from:

  • deep cervical arteries
  • intercostal arteries
  • lumbar arteries

• The great anterior medullary artery of Adamkiewicz arises from the aorta at lower thoracic and upper lumbar levels, enters the spinal cord from the left side, and is the major blood supply to the lower two-thirds of the cord.

Further detail

• Posterior spinal arteries are small in the upper three thoracic segments, and blockage of segmental or radicular arteries in this region can cause ischemia.

• The anterior spinal artery is small in the fourth thoracic and first lumbar segments, so blockage of segmental arteries in these segments can cause spinal cord ischemia.

💡 Memory Hook

Radicular or segmental artery blockage → ischemia in the dependent spinal cord territory

📊 Synthesis Tables

Major Arterial Territories

Artery	Main cerebral territory	Distinctive supply
Anterior cerebral artery	Medial cerebral cortex	Leg area of precentral gyrus
Middle cerebral artery	Lateral cerebral hemisphere	Most motor area except the leg area
Posterior cerebral artery	Medial and inferolateral temporal and occipital lobes	Visual cortex