The buoyancy of the brain in the CSF permits its relatively flimsy attachments to suspend it very effectively.> Protection: When the head receives a blow, the arachnoid slides on the dura & the brain moves, but its motion is gently checked by the CSF cushion and by the arachnoid trabeculae.> CSF pressure ranges from 180-10 mmg Hg); .4.4-7.3 mm Hg in newborns and < 200 mm Hg in children and adults.> Chemical stability drains metabolic wastes and maintains hemostasis.> Prevention of ischaemia is by reducing CSF pressure by decreasing its amount.> CSF pH is 7.30-7.36">