Cerebrospinal fluid (CSF) is the “blood” of the brain and spinal cord. It is produced in a structure called the choroid plexuses by ependymal cells.
Author: Anatomist90; Wikimedia Commons download Spring 2014; License: Creative Commons Attribution-Share Alike 3.0
Brain Anatomy. Author: OpenStax College; License: Creative Commons Attribution 3.0 Unported license.
These structures are found lining the ventricles of the brain. The majority of CSF is produced within the two lateral ventricles. The fluid moves from the lateral ventricles to the third ventricle which is found in the diencephalon. The fluid then moves down inferiorly through a relatively narrow canal called the cerebral aqueduct. After exiting the cerebral aqueduct, the CSF fluid is in the 4th ventricle. From the 4th ventricle, some CSF fluid continues inferiorly to fill the central canal of the spinal cord. The rest of the CSF fluid exits the 4th ventricle through the apertures (median and lateral). After exiting through these apertures, the CSF is now in the arachnoic space where it can travel all the way around the brain and spinal cord. This arachnoid space is found between the arachnoid mater and the pia mater. The total amount of CSF ranges from 100-600ml, but it is produced and reabsorbed at a rate of 500ml per day. Ependymal cells produce CSF from the blood plasma making the contents of the CSF almost identical to the blood plasma, with the exception of proteins (very little if any proteins found in normal CSF).
CSF is drained into a structure called the Superior Sagittal Sinus through small granulations called “Arachnoid Granulations”. The superior sagittal sinus drains the CSF with venus blood from the brain down and out of the skull via the jugular vein.
The function of the CSF can be summarized into five categories:
1. Buoyancy: The CSF helps to suspend the brain which reduces the effective weight by 95%. This allows the brain to exist in a state called neutral buoyancy. In less scientific terms, it allows the weight of the brain to not squish itself.
2. Electrolyte and circulatory balance: The CSF is very important in maintaining the homeostatic balance of electrolytes and glucose.
3. Protection: The properties of water allow the CSF to serve as a protection against jolts.
4. Circulation: Although the CSF is a very low-pressure system, it is an effective method of moving nutrients and waste around. It also helps to facilitate blood perfusion.
5. Waste removal: The CSF has proven essential in flushing metabolic waste. Recently researchers have shown that the flushing of waste is increased during sleep.
Sometimes a breach can occur, such as physical trauma or a lumbar puncture resulting in leakage of the CSF. This can change the pressure and allow the brain to not be as buoyant, which squishes on nerves and causes a variety of symptoms. In addition, in other cases a condition called hydrocephalus can occur. Hydrocephalus is the accumulation of CSF because of impaired flow or excessive production of CSF. This can also result in pressure changes and if it occurs in the fetus it can result in an enlarged head. Hydrocephalus in an adult must be immediately corrected.