The Ventricles and Cerebrospinal Fluid
There are four cavities in the brain, called ventricles. The ventricles are filled with cerebrospinal fluid (CSF), which provides the following functions:
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Absorbs physical shocks to the brain
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Distributes nutritive materials to and removes wastes from nervous tissue
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Provides a chemically stable environment
There are four ventricles:
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Each of two lateral ventricles (ventricles 1 and 2) occupies a cerebral hemisphere.
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The third ventricle is connected by a passage (interventricular foramen) to each of the two lateral ventricles.
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The fourth ventricle connects to the third ventricle (via the cerebral aqueduct) and to the central canal of the spinal cord (a narrow, central tube extending the length of the spinal cord). Additional openings in the fourth ventricle allow CSF to flow into the subarachnoid space.
A network of capillaries called the choroid plexus projects into each ventricle. Ependymal cells (a type of neuroglial cell) surround these capillaries. Blood plasma entering the ependymal cells from the capillaries is filtered as it passes into the ventricle, forming CSF. Any material passing from the capillaries to the ventricles of the brain must do so through the ependymal cells because tight junctions linking these cells prevent the passage of plasma between them. Thus, the ependymal cells maintain a blood‐CSF barrier, controlling the composition of the CSF.
The CSF circulates from the lateral ventricles (where most of the CSF is produced) to the third and then fourth ventricles. From the fourth ventricle, most of the CSF passes into the subarachnoid space, a space within the linings (meninges) of the brain, although some CSF also passes into the central canal of the spinal cord. The CSF returns to the blood through the arachnoid villi located in the dural sinuses of the meninges.