CSF flows through the subarachnoid space – the space between the two layers of meninges that are closest to the skull (the arachnoid layer and the dura mater). CSF also fills the brain's ventricles, and flows down the middle of the spinal cord (the central canal).
Contents[change | change source]
- Protein (though much less than plasma carries)
- Glucose (sugar)
- Neurotransmitters (chemical messengers)
- Electrolytes (salts), like sodium, potassium, calcium, magnesium, and chloride.
What CSF does[change | change source]
CSF helps the brain float[change | change source]
Being surrounded by CSF helps the brain float inside the skull, like a buoy in water. Because the brain is surrounded by fluid, it floats like it weighs only 2% of what it really does. If the brain did not have CSF to float in, it would sit on the bottom of the skull. The brain's weight would push the bottom of the brain against the skull. Blood would not be able to get to the bottom of the brain because the blood vessels would be getting crushed by the weight of the brain on top of them. Without getting blood (and the oxygen it carries), the neurons in the bottom of the brain would die.
CSF is the brain's cushion[change | change source]
When a person hits their head, CSF acts like the airbag in a car and can sometimes keep the brain from slamming into the inside of the skull. However, when a person hits their head very hard – in a car accident, for example – the CSF cannot protect the brain from hitting the skull. This can cause concussions, bleeding in the brain, brain damage, or even death.
CSF rinses toxins out of the brain[change | change source]
The brain's cells do chemical reactions to change one chemical to another chemical that the brain needs. Sometimes, after a chemical reaction, chemicals that the brain does not need are left over. These chemicals are called "waste products." For example, when the brain's cells use oxygen and glucose (sugar) to create energy, carbon dioxide (CO2) is left over. Too much carbon dioxide can poison the brain.
To keep waste products from building up in the CSF, the choroid plexuses make new CSF about four times a day. The old CSF drains out into the bloodstream, bringing waste products and toxins with it. In this way, the CSF rinses things that could hurt the brain out into the bloodstream. The bloodstream can then carry these chemicals to organs that can get rid of them, like the kidneys and the lungs. For example, the bloodstream carries carbon dioxide to the lungs, where it can be breathed out.
Testing CSF[change | change source]
Doctors can use samples of CSF to find out if a person has a brain infection, like meningitis, encephalitis, or syphilis. CSF samples can also show bleeding from certain parts of the brain. Swelling in the brain, caused by some inflammatory diseases like multiple sclerosis, can show in a CSF sample as well.
Results[change | change source]
Normal CSF should be clear and colorless, with no red blood cells, and very few white blood cells.
Signs of a brain infection include:
- CSF that is cloudy, yellow, or pink
- More protein in the CSF than normal
- More white blood cells in the CSF than normal
- Less glucose (sugar) in the CSF than normal
- Bacteria, viruses, fungi, or other pathogens in the CSF
Protein levels that are higher than normal can be a sign of inflammation in the brain. However, they can also be a sign of other problems, like a bleed in the brain; a brain tumor; epilepsy; and "acute alcoholism."
Problems with CSF[change | change source]
Too much[change | change source]
Head injuries and some diseases can make too much CSF build up in the brain. This is called hydrocephalus. The extra fluid puts pressure on (squeezes) the brain. This is called increased intracranial pressure. If the pressure gets high enough, the brain's blood vessels get crushed, and blood cannot get to the brain. If a person's brain does not get enough blood and oxygen, they will become unconscious and their brain cells will die. Eventually, the person will die.
Not enough[change | change source]
Some problems can cause CSF to leak out through a hole or tear in the dura mater (the layer of the meninges that is next to the skull and the bones of the spinal cord). CSF leaks are usually a complication of a lumbar puncture or certain kinds of surgery on the head, neck, or brain. However, an injury to the head or spine can also cause a CSF leak. Sometimes, doctors cannot find a cause for a CSF leak.
- Bacteria, viruses, or other pathogens can get in through the same hole CSF is leaking out of. This can cause brain infections like meningitis.
- Without enough CSF to float in, the brain sits on the bottom of the skull. The brain's weight can:
Related pages[change | change source]
References[change | change source]
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- "Hydrocephalus Fact Sheet". National Institute of Neurological Disorders and Stroke. United States National Institutes of Health. February 3, 2016. Retrieved February 6, 2016.
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- Schievink WI 2006. "Spontaneous Spinal Cerebrospinal Fluid Leaks and Intracranial Hypotension". Journal of the American Medical Association 295 (19): 2286–96. doi:10.1001/jama.295.19.2286. PMID 16705110.