Blood Supply

Blood Supply of the Nervous System

• Overview: The nervous system, made up of the brain and spinal cord, has a rich vascular network receiving approximately 15-20% of the body's total blood supply to meet its high metabolic demands.
    - Primary Blood Sources: Blood is supplied predominantly by two pairs of arteries:
      - Internal carotids for the forebrain.
      - Vertebral arteries for the brainstem and posterior brain.
    - Blood Supply Distribution:
      - About 80% of the brain's blood supply is from the internal carotid arteries.
      - The remaining 20% is provided by the vertebral arteries.
    - Critical Time Frames:
      - Loss of consciousness occurs within 15 seconds after blood flow to the brain stops.
      - Irreparable brain tissue damage occurs within 5 minutes of blood supply cessation.

Circulatory Systems of the Brain

• Circulatory Systems: There are two main circulatory systems providing blood supply to the brain:
    - Anterior Circulation:
      - Formed by the internal carotid arteries, supplying the anterior part of the brain.
    - Posterior Circulation:
      - Formed by a pair of vertebral arteries, it supplies the spinal cord, brainstem, cerebellum, and posterior parts of the brain.
    - Anastomoses: Both circulations connect at the base of the brain, forming the Circle of Willis.

Circle of Willis

• Definition: The Circle of Willis is a crucial anastomotic blood vessel structure at the base of the brain, named after Sir Thomas Willis.
    - Location: Connects the anterior circulation with the posterior circulation.
    - Composition: Comprised of the internal carotid and vertebral arteries.
    - Importance: Facilitates potential redirection of blood flow in case of arterial blockage.

Major Cerebral Arteries

• Cerebral Arteries: These arteries are the primary vessels that supply oxygenated blood to the brain, ensuring consistent cerebral perfusion.
    - The three main pairs are:
      - Anterior cerebral artery (ACA)
      - Middle cerebral artery (MCA)
      - Posterior cerebral artery (PCA)

Anterior Cerebral Artery (ACA)

• Origin: Arises from the internal carotid artery.

• Path: Runs in the supracollosal sulcus.

• Supplies: Medial portions of the frontal and parietal lobes.
    - Branches:
      - Callosal branches
      - Callosomarginal artery
      - Polar frontal artery
      - Orbitofrontal artery
      - Pericallosal artery
      - Other lateral and medial branches

Middle Cerebral Artery (MCA)

• Origin: Arises from the internal carotid artery.

• Path: Runs in the lateral sulcus.

• Function: The largest branch supplying most of the lateral cerebral cortex, including regions associated with motor and sensory functions.
    - Clinical Significance: Highly involved in strokes due to its size and coverage of critical brain areas.

Posterior Cerebral Artery (PCA)

• Origin: Arises from the basilar artery.

• Path: Travels in the calcarine sulcus.

• Supplies: The occipital lobe, thalamus, and inferior temporal lobe.

Blood Supply to the Brainstem

• Medulla Oblongata: Supplied by:
    - Vertebral artery
    - Anterior and posterior spinal arteries
    - Posterior inferior cerebellar artery
    - Basilar artery

• Pons: Supplied by:
    - Basilar artery
    - Anterior inferior cerebellar artery
    - Superior cerebellar artery

• Midbrain: Supplied by:
    - Posterior cerebral artery
    - Superior cerebellar artery
    - Basilar artery
    - Cerebellar Arteries: Three in total:
      - One arising from the vertebral arteries.
      - Two arising from the basilar artery.

Clinical Correlation: Stroke

• Definition: Stroke, also known as cerebrovascular accident (CVA), involves damage to any part of the brain due to a lack of blood supply.
    - Types of Stroke:
      - Ischemic Stroke: Diminished blood flow due to thrombosis or embolism.
      - Hemorrhagic Stroke: Involves bleeding (hemorrhage) in the brain.
    - Conclusion: Strokes disrupt the regular blood supply, leading to significant brain damage if not promptly addressed.