Meninges and Ventricular System

Meninges and Ventricular System

Meninges

  • Protective covering for the brain (from Greek meninx = membrane).
  • Three layers:
    • Dura mater
    • Arachnoid
    • Pia mater (adhered closely to surface of brain)

Dura Mater

  • 'Tough mother' (Dura like Durable, Mater like Maternal).
  • Outermost layer of meninges.
  • Dense and fibrous – tough.
  • Two layers.
  • Space between the layers forms venous sinuses – only in some places.
  • Inner layer forms the dural folds.
Special Features of Dura Mater
Dural Folds
  • Formed from the inner layer of dura mater.
  • Separate major divisions of brain.
  • Provide stability of the brain within cranium
  • Three of them:
    • Falx cerebri - separates cerebral hemispheres - median plane
    • Falx cerebelli - separates cerebellar hemispheres - median plane
    • Tentorium cerebelli - separates the cerebrum from the cerebellum - horizontal plane
Venous Sinus
  • Located where the two layers of dura mater separate.
  • Collecting veins.
  • They collect:
    • Venous blood from the brain
    • ‘Old’ CSF after it has cycled through the ventricular system

Arachnoid

  • 'Spider-like' layer.
  • Layer beneath the dura mater.
  • Layer above the pia mater.
  • Does not extend into sulci (‘valleys’).
  • Contains blood vessels (within the subarachnoid space, lying on top of pia mater).
Special Features of the Arachnoid
Subarachnoid Space
  • Space between the arachnoid and the pia mater.
  • Filled with cerebrospinal fluid (CSF).
Arachnoid Granulations
  • Perforate the inner layer of dura mater.
  • Transport “old” CSF from subarachnoid space into venous sinus
Arachnoid Trabeculae
  • Web-like strands of connective tissue that extend from the arachnoid to the pia mater, helping to keep the brain suspended.

Pia Mater

  • 'Delicate mother'.
  • Inner layer of the meninges.
  • Transparent and delicate.
  • Blood vessels in arachnoid sit on top of pia mater.
  • Adheres to brain and follows gyri and extends into sulci.

Meninges of the Spinal Cord

  • Dura mater, arachnoid mater, and pia mater surround the spinal cord, providing protection and support.
  • Dorsal root ganglion and spinous process of vertebra are key anatomical landmarks.

Ventricular System

  • Network of interconnected “spaces” (= ventricles) within the brain.
  • Filled with cerebrospinal fluid (CSF).
  • Spaces lined with ependymal cells, which circulate the CSF (waving cilia).
  • CSF is produced by the choroid plexus.
Components of the Ventricular System
  • Lateral ventricles (2)
    • Two of them
    • One in each cerebral hemisphere
  • Third ventricle (1)
    • Located in the diencephalon
  • Cerebral aqueduct (1)
    • Connects 3rd ventricle to 4th ventricle
    • Located in the midbrain
  • Fourth ventricle (1)
    • Located at the level of the cerebellum
  • Central canal (spinal cord)

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 of CSF
  • Start:
    • Lateral ventricles
    • 3rd ventricle
    • Cerebral aqueduct
    • 4th ventricle
    • Subarachnoid space
  • Within subarachnoid space, it flows around the brain and spinal cord.
  • Exit: through arachnoid granulations into venous sinus
Functions of CSF
  • Ultrafiltrate of plasma.
  • Provides protection and cushioning for brain.
  • Nourishment (vitamins, necessary ions).
  • Hormones from blood (Leptin, Prolactin).
  • Removal of metabolic waste (e.g., from neurotransmitter metabolism).
  • Removal of foreign particles (drugs etc).
  • Usually considered sterile, can contain microbes in infection.
  • "Brain washing” during sleep: Blood flow (red) increases before a wave of CSF (blue) washes toxins away
Lumbar Puncture
  • A procedure to collect a sample of CSF for diagnostic purposes.

Post-Lecture Quiz Review

  • Key topics include the layers of meninges, CSF circulation, and the location of ventricles to reinforce understanding.