The brain produces roughly 500 mL of cerebrospinal fluid per day. This fluid is constantly reabsorbed, so that only 100-160 mL is present at any one time.
The entire surface of central nervous system is bathed by a clear, colorless fluid called cerebrospinal fluid (CSF). The CSF is contained within a system of fluid-filled cavities called ventricles.
Ependymal cells of the choroid plexus produce more than two thirds of CSF. The choroid plexus is a venous plexus contained within the four ventricles of the brain, hollow structures inside the brain filled with CSF. The remainder of the CSF is produced by the surfaces of the ventricles and by the lining surrounding the subarachnoid space.
From: Blood—Cerebrospinal Fluid Barrier Cover of Basic Neurochemistry Basic Neurochemistry: Molecular, Cellular and Medical Aspects. 6th edition. Siegel GJ, Agranoff BW, Albers RW, et al., editors. Philadelphia: Lippincott-Raven; 1999. Copyright © 1999, American Society for Neurochemistry.
CSF serves several purposes:
1. Buoyancy: The actual mass of the human brain is about 1400 grams; however, the net weight of the brain suspended in the CSF is equivalent to a mass of 25 grams. The brain therefore exists in neutral buoyancy, which allows the brain to maintain its density without being impaired by its own weight, which would cut off blood supply and kill neurons in the lower sections without CSF.
2. Protection: CSF protects the brain tissue from injury when jolted or hit. In certain situations such as auto accidents or sports injuries, the CSF cannot protect the brain from forced contact with the skull case, causing hemorrhaging, brain damage, and sometimes death.
3. Chemical stability: CSF flows throughout the inner ventricular system in the brain and is absorbed back into the bloodstream, rinsing the metabolic waste from the central nervous system through the blood–brain barrier. This allows for homeostatic regulation of the distribution of neuroendocrine factors, to which slight changes can cause problems or damage to the nervous system. For example, high glycine concentration disrupts temperature and blood pressure control, and high CSF pH causes dizziness and syncope. To use Davson’s term, the CSF has a “sink action” by which the various substances formed in the nervous tissue during its metabolic activity diffuse rapidly into the CSF and are thus removed into the bloodstream as CSF is absorbed.
4. Prevention of brain ischemia: The prevention of brain ischemia is made by decreasing the amount of CSF in the limited space inside the skull. This decreases total intracranial pressure and facilitates blood perfusion.
5. Clearing waste: CSF has been shown by the research group of Maiken Nedergaard to be critical in the brain’s glymphatic system, which plays an important role in flushing metabolic toxins or waste from the brain’s tissues’ cellular interstitial fluid (ISF). CSF flushing of wastes from brain tissue is further increased during sleep, which results from the opening of extracellular channels controlled through the contraction of glials cells, which allows for the rapid influx of CSF into the brain. These findings indicate that CSF may play a large role during sleep in clearing metabolic waste, like beta amyloid, that are produced by the activity in the awake brain.
6. Endocrine medium for the brain: the CSF serves to transport hormones to other areas of the brain. Hormones released into the CSF can be carried to remote sites of the brain where they may act.
Typical Cerebrospinal Fluid (CSF) and Plasma Concentrations of Various Substances
Substance CSF Plasma CSF/plasma ratio
Electrolytes (mEq/l) Na+ 138 138 1.0
K+ 2.8 4.5 0.6
Cl− 119 102 1.2
HCO−3 22 24 0.9
Ca2+ 2.1 4.8 0.4
Mg2+ 2.3 1.7 1.4
PO3−4 0.5 1.8 0.3
Metabolites (mM) Glucose 3.3 5.0 0.7
Lactate 1.6 1.0 1.6
Pyruvate 0.08 0.11 0.7
Urea 4.7 5.4 0.9
Creatinine 0.09 0.14 0.7
Amino acids (μM) Alanine 26.0 350 0.1
Arginine 22.4 80.9 0.3
Aspartic acid 0.2 2.0 0.1
Asparagine 13.5 112 0.1
Glutamic acid 26.1 61.3 0.4
Glutamine 552 641 0.9
Glycine 5.9 283 0.02
Histidine 12.3 79.8 0.2
Isoleucine 6.2 76.7 0.1
Leucine 14.8 155 0.1
Lysine 20.8 171 0.1
Methionine 2.5 27.7 0.1
Ornithine 3.8 73.5 0.1
Phenylalanine 9.9 64.0 0.2
Phosphoethanolamine 5.4 5.1 1.0
Phosphoserine 4.2 8.3 0.6
Serine 29.5 140 0.2
Taurine 7.6 77.2 0.1
Threonine 35.5 166 0.2
Tyrosine 9.5 73.0 0.1
Valine 19.9 309 0.1
Proteins (mg/l) Total protein 350 70,000 0.005
Albumin 155 36,600 0.004
Transferrin 14.4 2,040 0.007
IgG 12.3 9,870 0.001
IgA 1.3 1,750 0.001
IgM 0.6 700 0.001
From: Constancy of the Internal Environment of the Brain Basic Neurochemistry: Molecular, Cellular and Medical Aspects. 6th edition.
Siegel GJ, Agranoff BW, Albers RW, et al., editors.
Philadelphia: Lippincott-Raven; 1999.
Copyright © 1999, American Society for Neurochemistry
The Table below lists the researched substances that enhance the cerebral spinal fluid:
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