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Overview of Brain Anatomy

• Cerebrospinal Fluid (CSF):

  • Surrounds the brain and spinal cord, provides buoyancy and protection.

  • Produced by choroid plexus, approximately 500ml/day.

• Blood-Brain Barrier:

  • A selective barrier that limits substance passage from blood to brain tissue, maintaining a stable environment.

Development of Major Brain Regions

• Cerebrum:

  • Largest part, involved in higher brain functions like thought and action.

• Diencephalon:

  • Contains thalamus and hypothalamus, crucial for sensory and hormonal control.

• Cerebellum:

  • Coordinates voluntary movements and maintains posture.

• Brain Stem:

  • Controls basic life functions like breathing, heart rate.

Protection of the Brain

• Meninges:

  • Three protective layers:

  • Dura Mater: Tough outer layer.

  • Arachnoid Mater: Middle layer, web-like.

  • Pia Mater: Delicate inner layer closely attached to the brain.

• Dural Septa:

  • Partitions of dura mater, including:

  • Falx Cerebri: Separates cerebral hemispheres.

  • Tentorium Cerebelli: Separates cerebellum from cerebrum.

Dural Venous Sinuses

• Large veins located between two layers of dura mater for venous drainage.

Ventricles of the Brain

• Ventricles:

  • Lateral Ventricles: Two cavities in the brain.

  • Third Ventricle: Central cavity, connected to lateral ventricles.

  • Cerebral Aqueduct: Connects third and fourth ventricles.

  • Fourth Ventricle: Located between the brain stem and cerebellum.

Cerebrospinal Fluid (CSF)

• Location of CSF:

  • Subarachnoid space, ventricles, central canal of spinal cord.

• Functions of CSF:

  • Buoyancy, protection, chemical regulation of CNS, reduction of brain weight.

• Production:

  • Produced by choroid plexus; maintains 100-160ml within ventricles & spaces.

• Reabsorption:

  • CSF is reabsorbed into the dural sinus via arachnoid granulations.

CSF Flow Pathway

• Flow:

  • Choroid Plexus → Lateral Ventricles → Third Ventricle → Cerebral Aqueduct → Fourth Ventricle → Apertures → Subarachnoid Space → Arachnoid Granulations → Dural Sinus → Veins (Internal Jugular) → Heart → Arteries (Carotids & Vertebral) → Choroid Plexus.

Impaired CSF Flow and Hydrocephalus

• Causes of Hydrocephalus:

  • Blockage (commonly at cerebral aqueduct), tumors, infections, hemorrhages, overproduction.

The Choroid Plexus & CSF Production

• Structure:

  • Composed of fenestrated capillaries and ependymal cells; maintains tight junctions.

• Function:

  • Filtration process allowing plasma components to enter CSF while restricting proteins.

Composition of CSF

• Similar to plasma but with:

  • Lower protein and altered ion concentrations (glucose, electrolytes).

Barriers Protecting the Brain

• Blood-CSF Barrier:

  • Controls substance movement into CSF with tight junctions between ependymal cells.

• Blood-Brain Barrier:

  • Restricts passage of materials from blood to brain; crucial for maintaining a stable environment.

Arterial Blood Supply to the Brain

• Main Arteries:

  • Internal Carotid Artery, Vertebral Artery, Common Carotid Artery, Aorta.

• Circle of Willis:

  • Anterior and posterior anastomosis of arteries providing collateral circulation.

The Blood-Brain Barrier

• Components:

  • Tight junctions between capillary endothelial cells, a basement membrane, astrocyte foot processes.

• Permeability:

  • Generally impermeable to antibiotics and some drugs but permeable to essential substances like glucose, oxygen, etc.

• Advantages:

  • Prevents infections but can hinder the treatment of neurological diseases.