Meninges

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  • Dura mater
    • outer layer lining the skull
  • Arachnoid mater
    • Space beneath is the subarachnoid space
      • contains cerebrospinal fluid (CSF)
    • contains blood vessels
  • Pia mater
    • covers the brain

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Subarachnoid space

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  • Space between the arachnoid and pia mater
    • contains CSF
  • Lies over the hemispheres
    • the space is narrow
  • At the cerebello-medullary angle
    • pia mater and arachnoid mater widely separated
    • At certain parts of the base of the brain, the arachnoid is separated from the pia mater by wide intervals, which communicate freely with each other
      • Cerebromedullary cistern

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  • Meninges covering the brain is continuous with the spinal cord
    • through the foramen magnum
  • Subarachnoid space around the brain continuous with spinal cord

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  • The spinal cord ends at
    • lower border of L1 vertebrae
  • Subarachnoid space extends to
    • lower border of S2 vertebrae
  • Lumbar cistern
    • a subarachnoid space in the spinal cord, where the dura mater ends, filled with cerebrospinal fluid
    • enlargement of the subarachnoid space between the conus medullaris of spinal cord (about vertebral level L2) and inferior end of subarachnoid space and dura mater (about vertebral level S2); occupied by the posterior and anterior roots constituting the cauda equina, the terminal filum, and cerebrospinal fluid
    • are where lumbar puncture is done
      • between L2-L3 or L3-L4 levels
      • so that won’t cause damage to the spinal cord

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  • Arachnoid granulations/Arachnoid villi
    • are prolongations of arachnoid mater
    • forming a tuft through the dura mater
    • into the superior sagittal sinus
    • Function:
      • transfers CSF from subarachnoid space into the venous system

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Ventricles of the brain

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  • Lateral ventricles
    • 2 ependymal (thin epithelial membrane) lined cavities
      • of cerebral hemispheres
    • Consists of
      • Anterior horn
      • Body
      • Posterior horn
      • Inferior horn
    • Each lateral ventricles connected to 3rd ventricles by
      • Interventricular foramen (of Monro)
  • 3rd ventricles
    • a slit like cavity separating the diencephalon into 2 equal parts
  • 4th ventricles
    • tent shaped space between
      • pons & medulla – INFRONT
      • cerebellum – BEHIND
    • 2 roofs
      • ventral
      • dorsal
    • Communicates with
      • median aperture
        • foramen of Magendie
        • drains CSF from the fourth ventricle into the cisterna magna/cerebromedullary cistern
          • back into subarachnoid space
      • lateral apertures
        • foramen of Lushka
        • drains CSF from the fourth ventricle into the cisterna magna/cerebromedullary cistern
          • back into subarachnoid space
    • Floor of the 4th ventricle
      • Facial colliculus
        • facial nerve fibres looping around the abducent nucleus
      • Hypoglossal trigone
        • hypoglossal nucleus
      • Vagal trigone
        • vagus nucleus

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Cerebrospinal fluid

  • Total volume circulation at a time
    • 130 ml
  • Formation of CSF
    • 80% from choroid plexus
      • located in the lateral, 3rd & 4th ventricles
    • The rest from the ependymal cells
      • lining the ventricles
  • Rate of production
    • 0.5ml per min
  • Pressure measured in the lumbar cistern
    • in recumbent position
    • 70 – 150 mm H20
  • Composition of CSF
    • clear and colourless liquid
    • glucose 1/2 of that in blood
      • 50-85 mg/100ml
    • Protein
      • 15 – 30 mg/100ml
    • Cells
      • 1-3 cells / Cu mm
      • (lymphocytes)
  • Functions
    • Protects CNS from trauma
      • Buoyancy of CSF reduces the concussion damage to the brain when the cranium moves suddenly
    • Nourishes the brain
    • Removes metabolites from CNS
    • Carries pineal secretions to pituitary gland
  • CSF secretion
    • Choroid plexus
      • vascular pia projecting into ventricles as a fringe covered with ependymal covering
      • the area on the ventricles of the brain where CSF is produced by modified ependymal cells
      • secretes major part of the CSF
      • Present in all components of the ventricular system (except cerebral aqueduct, occipital & frontal horn of lateral ventricles)
        • Body & inferior horn (of lateral ventricles)
        • Roof of (3rd ventricle)
        • Inferior part of (4th ventricle)
    • Tela choroidea
      • 2 layers of pia with high vascular plexus
      • in between coming into contact with the ependymal layer of the ventricles
  • CSF circulation
    • within the ventricles
      • by ciliary action of the ependymal cells
    • within the subarachnoid space
      • by the pulsation of the arteries on the surface of brain & spinal cord
  • CSF absorption
    • When the CSF pressure exceeds venous sinus pressure
      • CSF seeps through channels in arachnoid villli (arachnoid granulations) into venous sinus
        • If venous sinus pressure higher that CSF pressure
          • tips of the villi are compressed
          • so that the channels are closed
          • prevents reflux of blood into CSF

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