What is CSF:

Cerebrospinal fluid (CSF) is a crystal clear ultra-filtrate of plasma that is continuous with the brain’s ECF (i.e. CSF is in direct communication with the ECF of the brain).

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CSF is a clean, clear fluid that is derived from blood plasma but is filtered to remove most proteins and cells. Think of it as a highly refined version of blood plasma, specifically for the brain and spinal cord

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CSF is produced by the choroid plexus which is located in the lateral ventricle and the 4th ventricle. The CSF from these ventricles then flows into the subarachnoid space and travels down the spinal cord to the thecal sac (ends at around S2).

CSF is reabsorbed into the meningeal vasculature (mainly via the arachnoid granulations/villi and the dural venous sinuses). The total volume of CSF turns over/is renewed every 5-6hrs.

Function of CSF:

• provides mechanical support by acting as a shock absorber- it cushions the brain and spinal cord from trauma
• ECF of the brain separated from the vascular space by the Blood Brain Barrier (BBB). Because of this separation, the brain needs a special fluid system (CSF) to deliver nutrients, remove waste products and maintain proper chemical balance.

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Basically the CSF compensates for the lack of free access to blood.

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The blood brain barrier:

The BBB is a selective barrier between the bloodstream and the brain tissue that carefully controls the brains ECF environment.

Properties of the BBB:

• Protects brain from toxins

• Almost impermeable to

  –Large molecules such as plasma proteins

  –Water soluble molecules

  –Charged molecules  such as H+, Na+

• Highly permeable to CO2, O2, water, lipophilic substances

The permeability of the BBB is influenced by:

–Inflammation (inflammatory mediators can make the BBB leaky)

–Immaturity (in newborns, especially premature infants, the BBB is not fully developed, so it’s more permeable)