Brain anatomy: ventricles, meninges and CSF

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Brain anatomy ventricles, meninges and CSF
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VENTRICULAR SYSTEM

• Within the brain is a communicating system of
  cavities that are lined with ependyma and filled
  with cerebrospinal fluid (CSF)
• There are
• two lateral ventricles,
• the third ventricle,
• the cerebral aqueduct,
• and the fourth ventricle within the brain stem.

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MENINGES SPACES

• Three membranes, or meninges, envelop the brain
• the dura,
• the arachnoid,
• and the pia.
• The dura (outer membrane) is separated from the
  thin arachnoid by a potential compartment, the
  subdural space, which normally contains only a
  few drops of CSF.
• An extensive subarachnoid space containing CSF
  and the major arteries separates the arachnoid
  from the pia, which completely invests the brain.
  

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Cerebrospinal Fluid

• The CSF provides mechanical support of the brain
  and acts like a protective water jacket.
• It controls brain excitability by regulating the
  ionic composition, carries away metabolites and
  provides protection from pressure changes.
  Normal CSF is clear, colorless, and odorless.
• The CSF is present in a system that comprises two
  communicating parts.
• The internal portion of the system consists of
  two lateral ventricles, the interventricular
  foramens, the third ventricle, the cerebral
  aqueduct, and the fourth ventricle.
• The external part consists of the subarachnoid
  spaces and cisterns.
• Communication between the internal and external
  portions occurs through the apertures of the
  fourth ventricle.

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CSF 2

• In adults, the total volume of CSF in all the
  spaces combined is normally about 150 mL.
• Between 400 and 500 mL of CSF is produced and
  reabsorbed daily.

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Blood-Brain Barrier

• Collectively, the blood vessels within the brain
  have a very large surface area that promotes the
  exchange of oxygen, carbon dioxide, amino acids,
  and sugars between blood and brain.
• The blood-CSF barrier is formed by active
  transport from the blood vessels to the brain-
  Epithelial cells of joined by tight junctions,
  form a continuous layer that selectively permits
  the passage of some substances but not others.
• Why do we need this?