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Cerebrospinal Fluid. Formation. CSF is the fluid which fills the ventricles and subarachnoid space in the CNS. In humans, the volume of CSF is about 150 mL The rate of CSF production is about 550 mL /day. Formation. Formation.
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Formation • CSF is the fluid which fills the ventricles and subarachnoid space in the CNS. • In humans, the volume of CSF is about 150 mL • The rate of CSF production is about 550 mL/day.
Formation • CSF is formed continuously by the choroid plexus in two stages. • Plasma is passively filtered across the choroidal capillary endothelium. • Secretion of water and ions across the choroidalepithelium • The composition of CSF is essentially the same as that of brain extracellular fluid (ECF).
The arrows show the pathway of cerebrospinal fluid flow from thechoroid plexuses in the lateral ventricles to the arachnoidalvilliprotruding into the dural sinuses.
Absorption • The CSF in the ventricles. • Flows through the foramens of Magendie and Luschka to the subarachnoid space • Absorbed through the arachnoidvilli into veins, primarily the cerebral venous sinuses.
Function Buoyancy • The brain weighs about 1400 g in air, but in its "water bath" of CSF it has a net weight of only 50 g. • The buoyancy of the brain in the CSF permits its relatively flimsy attachments to suspend it very effectively. • Allows the brain to maintain its density without being impaired by its own weight, which would cut off blood supply and kill neurons in the lower sections without CSF.
Function Protection • CSF protects the brain tissue from injury when hit. • It absorbs all the shock from the trauma. • When the head receives a blow, the arachnoid slides on the dura and the brain moves, but its motion is controlled by the CSF which acts as a cushion andprevents the damage of brain
Function Prevention of brain ischemia • Amount of CSF in the brain can effect intracranial pressure and can control blood flow to brain
Function Chemical stability • CSF has a "sink action" by which the various substances formed in the nervous tissue during its metabolic activity diffuse rapidly into the CSF and are thus removed into the bloodstream as CSF is absorbed.
Hydrocephalus • This may cause increased intracranial pressure inside the skull • Progressive enlargement of the head • Convulsion • Tunnel vision • Mental disability • Hydrocephalus can also cause death.
Lumbar puncture • CSF is collected either by lumbar puncture. • In lumbar puncture, the lumbar puncture needle is introduced into subarachnoid space in lumbar region, between the third and fourth lumbar spines.
Procedure • The reclining body is bent forward, so as to flex the vertebral column as far as possible. • The highest point of iliac crest is determined by palpation. • A line is drawn on the back of the subject by joining the highest points of iliac crests of both sides. • Opposite to midplane, this line crosses the fourth lumbar spine. • After determining the area of fourth lumbar spine, third lumbar spine is palpated. • The needle is introduced into subarachnoid space by passing through soft tissue space between the two spines.
Uses of Lumbar puncture • Collecting CSF for diagnostic purposes • Injecting drugs (intrathecal injection) for spinal anesthesia, analgesia and chemotherapy • Measuring the pressure exerted by CSF.