How we change what others think, feel, believe and do
The brain contains a series of small hollow chambers called ventricles.
There is one large lateral ventricle in either hemisphere. The third ventricle is central and forward, whilst the fourth ventricle lies further back and below (in the hindbrain). The third and fourth ventricles are connected by the cerebral aqueduct (also called the Aqueduct of Sylvius).
Ventricles are filled with cerebrospinal fluid (CSF), which also fills other gaps around the brain as well as the central canal of the spinal cord. CSF also fills the sub-arachnoid space in the protective meninges sheath.
A major use of CSF is in cushioning the CNS. The brain weighs about 1400g (three pounds). By floating the brain in this fluid, this mass is reduced to about 80g in effect.
It also helps avoid excessive pressure in the skull by draining away when pressure increases. This also helps ensure that the blood supply to the brain is not cut off.
CSF is extracted from the blood and manufactured by modified ependymal cells in a special tissue called the choroid plexus, which extends into all four ventricles. It circulates through the third and fourth ventricles before passing out into the rest of the brain and spinal cord.
The CSF in the system is constantly replaced, with a 'half life' of about three hours. It drains back into the blood via arachnoid granulations.
Obstructive hydrocephalus is a condition where flow of CSF is interrupted, such as where a tumor constricts passages or where a child is born with a small cerebral aquaduct. This results in enlargement of ventricles as the CSF is unable to escape. If not treated, this can be fatal.
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