Anatomy of the Meninges

Layers of Protective Covering

• Skull: Outer protective case.
• Periosteum: Dense connective tissue lining the skull.
• Meninges: Three layers:
  1. Dura mater:
     • Tough, dense irregular connective tissue.
     • 3 Dural Folds (sheets of dura mater meningeal layer):
       • Falx cerebri: Sickle-shaped, divides the two cerebral hemispheres.
       • Tentorium cerebelli: Separates cerebrum and cerebellum.
       • Falx cerebelli: Divides the right and left cerebellar hemispheres.
  2. Arachnoid mater:
     • Spider-web-like trabeculae connecting to pia mater.
  3. Pia mater:
     • Innermost, closely adheres to brain tissue.

Function of Dural Meningeal Folds

• Prevent excessive movement of the brain.
• Support blood vessels and prevent shearing injuries.

Significance of the Tentorium Cerebelli

• Acts as a divider:
  • Supratentorial region: Above the tentorium.
  • Infratentorial region: Below the tentorium, including the cerebellum and brainstem.
• Lesion location:
  • Supratentorial: Effects localized to cerebral cortex.
  • Infratentorial: Affects cerebellum and/or brainstem
    • Cerebellar lesions: result in loss of coordination, balance, and/or posture
    • Brainstem lesions: affect vital functions, risk of coma or death.

Location of Brain Lesions: Supra- and Infratentorial

Definitions

• Supratentorial lesion:
  • Located above the tentorium cerebelli (dural fold of the meningeal dura mater).
  • Usually affects cerebral cortex.
  • Causes specific neurological deficits depending on lesion site.
• Infratentorial lesion:
  • Located below the tentorium cerebelli (dural fold of the meningeal dura mater).
  • Involves cerebellum or brainstem.
  • More dangerous because it affects vital centers controlling heart rate, breathing, and consciousness.

Implications

• Growth or bleeding in either area can spread and cause widespread damage.
• Damage to brainstem (midbrain, pons, medulla):
  • Critical vital functions are controlled here.
  • Damage can lead to coma or death.

Effects of Damage Based on Location

• Damage above the tentorium:
  • Usually discrete and localized.
  • Cause specific neurological deficits.
• Damage below the tentorium:
  • Affects brainstem, which controls:
    • Heart rate, Force of Contraction.
    • Vasomotor control of vasodilation and vasoconstriction
    • Breathing.
    • Consciousness (reticular activating system).
  • In addition to ascending and descending tracts that pass through the brainstem carrying sensory and motor information between the central nervous system (CNS) and peripheral nervous system (PNS)
  • Can lead to widespread impairment and coma.

Summary

• The location of brain lesions determines severity and symptoms.
• The tentorium cerebelli divides the brain into critical regions with different risks.
• Damage to brainstem is particularly serious due to its role in vital functions.