CNS Blood Supply

The brain is a highly vascular organ characterized by a profuse blood supply consisting of a densely branching arterial network.
It has a high metabolic requirement, receiving 15-20% of the cardiac output in healthy adults.
Blood flow to the brain serves critical functions:
- Delivers oxygen, glucose, and other nutrients to nervous tissues.
- Removes carbon dioxide, lactic acid, and other metabolic by-products.
Continuous blood flow is critical; interruption of supply for more than a few minutes can lead to ischemic cell death, causing permanent neurological damage (such as stroke).

Blood supply to the brain derives from two pairs of interconnected arteries:
  - Internal Carotid Arteries (ICA)
    - Supply the anterior circulation of the brain.
    - Major branches supply the majority of the cerebral hemispheres.
  - Vertebral Arteries (VA)
    - Supply the posterior circulation of the brain.
The brain can be divided into two cerebral hemispheres, with each supplied by one ICA (left and right) and two VAs that unite to form the basilar artery.
The arteries are responsible for supplying blood to both the anterior and posterior circulations:
- Anterior circulation: Primarily supplied by ICA and its branches.
- Posterior circulation: Primarily supplied by the vertebrobasilar system.

Petrous Part
   - First division extending from the base of the carotid canal to the apex of the petrous bone.
   - Branches include:
     - Caroticotympanic a.
     - Pterygoid a.
Cavernous Part
   - Second division; follows a horizontal S-shaped path through the cavernous sinus.
   - Branches include:
     - Meningeal a.
     - Hypophyseal a.
Intracranial/Cerebral Part
   - Third division; commences upon piercing the dura mater and arachnoid mater.
   - Branches include:
     - Ophthalmic a.
     - Anterior choroidal a.
     - Posterior communicating a.
     - Anterior cerebral a.
     - Middle cerebral a.

Pre-terminal Branches:
  - Ophthalmic a.
  - Choroidal a.
  - Posterior communicating a.
Terminal Branches:
- Middle cerebral a.
- Anterior cerebral a.

Supplies posterior circulation of the brain.
Supplies:
  - Upper spinal cord.
  - Brainstem and cerebellum.
  - Posterior parts of the cerebral hemispheres.
Branches from the first part of the subclavian artery, advancing through the first six cervical vertebrae's transverse foramina.
Enters the skull through the foramen magnum and joins at the medulla-pontine junction to form the basilar artery.

Supplied by the:
  - Superior cerebellar arteries (SCA).
  - Anterior inferior cerebellar arteries (AICA).
  - Posterior inferior cerebellar arteries (PICA).

Formed by the anastomosis of the terminal branches of both ICA and VA on the inferior surface of the brain.
Provides anastomotic connections between anterior and posterior circulations, ensuring collateral flow in events of arterial incompetency.
Comprises:
- Anterior cerebral arteries (ACA) linked by the anterior communicating artery.
- Posterior cerebral arteries (PCA) connected to the ICA by the posterior communicating artery.

Drain the cerebral cortex and subcortical white matter.
Includes:
  - Superior cerebral veins draining superolateral and medial surfaces via the superior sagittal sinus.
  - Superficial middle cerebral vein draining the lateral aspect into the cavernous sinus.
  - Deep middle cerebral vein draining the insula.
  - The basal vein drains to the great cerebral vein and empties into the straight sinus.

Drain areas including:
  - Choroid plexuses of the third and lateral ventricles.
  - Periventricular region.
  - Diencephalon and basal ganglia.
Formed by the union of the thalamostriate vein and choroid vein, eventually uniting to form the great cerebral vein that drains into the straight sinus.

Midbrain is drained by veins into the basal or great cerebral veins.
Pons by veins opening into the basal vein or adjacent sinuses.
Medulla oblongata drained by veins into spinal veins or local sinuses.
Cerebellum drained by veins emptying into the great cerebral vein or adjacent venous sinuses.

Supplied by three longitudinally running vessels and segmental branches from the vertebral artery:
- Anterior spinal artery.
- Two posterior spinal arteries.
Reinforced by segmental arteries entering through the intervertebral foramina.

Comprises several conducting veins, which are valveless with the following pathways:
- Central/sulcal veins → anterior and posterior spinal veins → internal vertebral venous plexus → systemic circulation.

Anterior Cerebral Artery (ACA) Occlusion:
- Results in contralateral hemiparesis and hemisensory loss affecting primarily the leg.
- Vascular territory involved is the anterior circulation.
Middle Cerebral Artery (MCA) Occlusion:
- Results in aphasia if in the left hemisphere, which can be Broca’s or Wernicke’s depending on the area affected.
Posterior Cerebral Artery (PCA) Occlusion:
- Causes contralateral homonymous hemianopia and visual agnosia, involving mainly the visual cortex.

Identify the arteries of the Circle of Willis.
Discuss potential occlusions with various symptoms and areas involved, based on clinical cases presented.

Multiple choice questions based on blood supply, arteries involved, and effects of occlusion.

Trans Operations and lectures for arterial blood supply to the brain and spinal cord, as well as fundamental texts in clinical anatomy and neuroscience.

Discuss the origin and course of the Internal Carotid System and the Vertebro-Basilar System.
Describe arterial and venous distribution to the brain and spinal cord.
Explain clinical correlations involving specific vascular occlusions and their neurological effects.