Lecture 21 - Meninges and Ventricular System

• Meninges


  Protective covering for the brain (from Greek meninx - membrane). Lie between the skull and surface of the brain.
• Meninges are comprised of three layers
• Dura Mater


  The outermost, most superficial layer
• Arachnoid


  Middle layer
• Pia Mater


  Innermost layer, adhered very closely to the brain, very thin layer
• Subarachnoid space


  • Created by thin spidery legs under the clear arachnoid membrane
• Pia mater enters indentations on the surface of the brain
• Dura Mater


  Tough, fibrous, outermost layer
• Dura Mater


  • Houses two layers, an outer and an inner
  • Space between the layers form venous sinuses these only occur in some places where the layers seperate
  • The inner layers form the dural folds
• Dural folds


  • Formed from inner layer of dura mater
  • Separate major divisions of brain
  • Provide stability of the brain within cranium
• Types of Dural folds

  • Falx Cerebri
  • Falx Cerebelli
  • Tentorium Cerebelli
• Venous Sinus


  • Located where the two layers of dura mater separate
  • Collecting veins
  • They collect venous (deoxygenated) blood from the brain, and old' CSF after it has cycled through the ventricular system
• Arachnoid (Spider - like) Layer


  Layer beneath the dura mater, named because it has a spider-like appearance
• Arachnoid Layer


  • Layer beneath the dura mater
  • Layer above the pia mater
  • Does not extend into sulci ('valleys')
  • Contains 2 special features: The subarachnoid spacean and the arachnoid granulations
  • Contains blood vessels (within the subarachnoid space, lying on top of pia mater)
• Subarachnoid space


  A special feature of the arachnoid, filled with cerebrospinal fluid (CSF)
• Arachnoid granulations


  Perforate the inner layer of the dura mater, act as one way valves, transport old CSF from subarachnoid space into the venous sinus
• Pia Mater


  Inner layer of the meninges, transparent and delicate, blood vessels in arachnoid sit on top of pia mater, sometimes break through to provide blood to the brain, adheres to brain and follows gyri and extends into sulci
• Ventricular system


  • Network of interconnected "spaces" (ventricles) within the brain
  • Filled with cerebrospinal fluid (CSF), which nourishes and protects the brain
  • Spaces lined with ependymal cells, which circulate the CSF (waving cilia) - all code inside surface of the ventricles
  • CSF is produced by the choroid plexus, within ventricles to make CSF to fill space
• Ventricles


  • Two lateral ventricles
  • Third ventricle
  • Fourth ventricle
• Cerebral aqueduct


  Narrow channel that connects the third ventricle of the diencephalon to the fourth ventricle, located in the midbrain and enables cerebrospinal fluid to enter the fourth ventricle
• Cerebrospinal Fluid (CSF)


  • Produced by choroid plexus within the ventricles
  • Surrounds the CNS, within subarachnoid space
  • Provides support and cushion
  • Transports nutrients and waste
• Circulation path of CSF

  1. Lateral ventricles

  2. 3rd ventricle

  3. Cerebral aqueduct

  4. Fourth ventricle

  5. Subarachnoid space

  6. Exits via arachnoid granulations into the venous sinus