A clear fluid in the brain called cerebrospinal fluid (CSF) forms a crucial component of the central nervous system, distributing nutrients, removing waste, and providing a shock-absorbing layer for fragile brain tissue. This multipurpose substance is stored, and primarily produced, in four hollow chambers deep inside the skull called ventricles.

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The four ventricles are connected to each other, and surround the central column of the spinal cord, through a system of ducts. Together, this network comprises what is known as the ventricular system.

In addition to its other roles, CSF provides buoyancy to the brain—in essence, allowing it to “float” in the skull surrounded by fluid. This reduces the stress that the weight of the 3-pound brain would otherwise place on the spine and prevents compression of the brain against the bony skull and spine.

Each ventricle plays a somewhat different role. The left and right ventricles are located in the cerebrum, near the front of the brain, and produce 70 percent of the body’s CSF. The third ventricle, in the middle section of the brain, also produces CSF and serves a different section of the organ. The fourth ventricle, at the back of the brain, provides openings allowing CSF to flow into the space surrounding the brain and into the spinal cord.

Just as our blood stream should not be too high or too low, neither should CSF pressure. To keep this pressure at a normal level (between 100 and 150 millimeters of water), CSF is absorbed back into the bloodstream through structures called arachnoid villi at roughly the same rate it is produced in the ventricles. If something prevents the circulation and absorption of CSF and it backs up in the brain, however, the ventricles will swell and push on the surrounding tissue—a condition called hydrocephalus, or water on the brain.

ADDITIONAL FACTS

  1. CSF typically contains high amounts of salt, sugar, and lipids, but low amounts of protein. Large amounts of protein in a sample of CSF (collected by a lumbar puncture, or spinal tap) may indicate that the body’s blood-brain barrier is not working properly.
  2. The third ventricle divides the thalamus into symmetrical halves.
  3. The total volume of CSF in the body at one time is usually 125 to 150 milliliters.