Major Blood Supply to the Brain Study Notes

Major Blood Supply to the Brain

Overview of Blood Supply

• The brain receives almost 15% of the total cardiac output.

• Blood supply to the brain arises from two sets of arteries:

  • Vertebral arteries (20% supply):

  • Arise from subclavian arteries.

  • Travel through foramen transversarium in the cervical spinal cord.

  • Enter the skull via the foramen magnum.

  • Internal carotid arteries (80% supply):

  • Branches of the common carotid artery.

  • Enter the skull through the carotid canal.

Cerebrovascular Disease

• Cerebrovascular disease is the third most common cause of death in Australia.

• In 2022-2023, there were approximately 45,000 emergency department admissions due to stroke.

• Important time frames regarding brain ischaemia:

  • 10-15 seconds: Loss of consciousness.

  • 20 seconds: Loss of electrical activity.

  • 5 minutes: Irreversible brain damage.

Vertebral Artery Supply

• The vertebral arteries join to form the basilar artery, referred to as the vertebral basilar system.

• Key branches of the vertebral artery:

  • Anterior spinal artery: Supplies spinal cord and part of the medulla.

  • Posterior inferior cerebellar arteries (PICA): Supply part of the brainstem and cerebellum.

Histological Supply Territories in the Medulla

• Schematic of medulla shown with the following supply territories:

  • Anterior spinal artery (orange): Supplies ventromedial aspect of the medulla.

  • Vertebral artery (blue): Supplies ventralateral aspect of the medulla.

  • PICA (green): Supplies dorsal lateral medulla and posterior inferior cerebellum.

Basilar Artery Structure

• The basilar artery sits on the ventral surface of the pons:

  • Provides penetrating branches to supply the pons.

  • Major branches:

  • Anterior inferior cerebellar arteries (AICA): Supply dorsal pons and cerebral undersurface.

  • Superior cerebellar arteries: Supply deep and superior parts of cerebellum and parts of middle cerebellar peduncle.

Termination of the Basilar Artery

• The basilar artery terminates into:

  • Left and right posterior cerebral arteries:

  • Supply the midbrain, occipital lobe (primarily), and undersurface of the temporal lobe.

Internal Carotid Artery System

• The internal carotid arteries supply all of the cerebral cortex except for the occipital lobe.

• Major branches of the internal carotid artery:

  • Anterior cerebral artery (ACA): Supplies the medial surface of the cerebrum.

  • Middle cerebral artery (MCA): Supplies the lateral surface of the cerebrum.

Arterial Supply Diagram

• Internal carotid artery divides as follows:

  • MCA (lateral): Supplies most of the lateral surface of the brain.

  • ACA (medial): Supplies the very top edge of the lateral surface.

  • Posterior cerebral artery (PCA): Supplies posterior and inferior edges of the brain.

Somatosensory and Motor Cortex

• Motor and sensory areas supplied by:

  • Anterior cerebral artery: Supplies trunk and legs (loss leads to anaesthesia and loss of motor control in lower body).

  • Middle cerebral artery: Supplies upper body, arms, and head (loss leads to anaesthesia and loss of motor control in upper body).

• Posterior cerebral artery: Supplies visual cortex (blockage results in blindness).

Circle of Willis

• Arteries also connect through small communicating arteries:

  • Posterior communicating arteries: Connect posterior cerebral arteries to internal carotid arteries.

  • Anterior communicating arteries: Connect the two anterior cerebral arteries.

• This network of vessels is known as the Circle of Willis.

  • Enables collateral circulation between vertebral basilar system and internal carotid system.

Wet Specimen Observations

• Wet specimens show:

  • Circle of Willis configuration with arteries visible:

  • Anterior spinal artery

  • Vertebral arteries forming the basilar artery

  • Anterior and posterior communicating arteries.

Concluding Summary

• Summary of arterial systems covered:

  • Vertebral basilar system supplies brainstem and cerebellum.

  • Internal carotid system supplies cerebral cortex (except occipital lobe).

  • Connection between systems through Circle of Willis facilitates efficient blood supply to the entire brain.

• Ensure to identify the origin, course, and branches of the internal carotid artery and basilar artery.

• Describe the distribution of both the internal carotid artery and the vertebral basilar system thoroughly.