Cerebrospinal Fluid: Flow, Function and Why It Matters

Cerebrospinal fluid, or CSF, is one of the most important fluids in the body. It surrounds the brain and spinal cord, fills the ventricles inside the brain, and works as a cushion, a transport system and a waste-removal route all at once.

Where it comes from and where it goes

CSF is made mostly by the choroid plexus inside the brain’s ventricles. About 500 mL is produced each day, even though only 125–150 mL is present at any moment, so the fluid is replaced three to four times daily. It flows through the ventricles, around the brain and spinal cord, and drains mainly through the arachnoid granulations into the venous sinuses, with additional drainage through lymphatic pathways.

What moves it

CSF is pushed along by the heartbeat, by breathing, and by slower oscillations in the blood vessels. Researchers still debate how much each one contributes, and imaging studies show breathing plays a larger role than once thought. CSF also moves back and forth between the skull and the spinal canal through the opening at the base of the skull with each heartbeat, which helps absorb the pressure of every pulse.

Why it matters

CSF cushions the brain, helps manage pressure inside the skull, and carries away metabolic waste. Waste clearance appears to increase during sleep, which is one reason sleep matters for brain health.

Standing up changes the plumbing

The brain floats in CSF, which cuts its effective weight from about three pounds to about three ounces. CSF drains into the venous sinuses, and where that blood leaves the head depends on posture. Lying down, most of it exits through the jugular veins. Standing, the jugular veins narrow and a larger share travels down the network of veins along the spine instead. That route passes through the base of the skull and the upper neck, which is one reason I look at the occiput and the top of the neck together.

CSF and cranial adjusting

Cranial practitioners have long treated CSF as central. Sutherland built his concept of the primary respiratory mechanism around its fluctuation. In my practice I think of CSF flow, the membranes it moves through, and the cranium that surrounds them as one system, and that’s a large part of why I assess and adjust the cranium. Direct evidence in humans that cranial adjusting changes CSF flow is still limited, and it’s the research I’d most like to see.

References

• Valdueza JM, et al. Postural dependency of the cerebral venous outflow. Lancet. 2000;355(9199):200–201.
• Gisolf J, van Lieshout JJ, van Heusden K, Pott F, Stok WJ, Karemaker JM. Human cerebral venous outflow pathway depends on posture and central venous pressure. J Physiol. 2004;560(Pt 1):317–327.
• Flanagan M. Craniospinal Hydrodynamics in Neurodegenerative and Neurological Disorders. New York: Nova Science Publishers; 2016.
• Flanagan M. The Downside of Upright Posture: The Anatomical Causes of Alzheimer’s, Parkinson’s, and Multiple Sclerosis. Minneapolis: Two Harbors Press; 2010.