In 1925 the famous neurosurgeon Dr. Harvey Cushing published one of his lectures in Lancet in which he described cerebrospinal fluid (CSF) as the third circulatory system of the brain. The dynamic flow of the third circulatory system of the brain and cord can be compared to a current that comes out of large lakes and rivers fed by rainfall and streams and connected by a gulf to a much larger ocean. Winds whip up the water and the currents and tides collide in the gulf, which results in waves.
The sketch above on the right shows the Great Lakes of North America where rain water gathers from surrounding hills and streams. The water is carried by currents that flow out of the lakes by way of the Saint Lawrence River where it enters the Saint Lawrence Gulf, which is continuous with the ocean. Compared to the vast Atlantic Ocean, all the Great Lakes combined are much smaller in size and capacity.
While the current flows out of the Great Lakes to the ocean the tide of the ocean it runs into varies with the moon and time of day. Sometimes it moves out to sea in the same direction as the flow of the Saint Lawrence. Othertimes the tide comes in and flows against the river’s current. This creates conflict and turbulance where the two meet in the gulf. Over time the water turbulance caused by the ebb and flow of the tide erodes the coasts of Northern America and helps shape its shorelines.
Cerebrospinal fluid (CSF), a filtrate of blood, is basically water with some sugar and other elements mixed in. CSF is produced in the four ventricles (chambers) of the brain. From there it follows through various channels and into every nook and cranny of the brain. It also flows down through the spinal cord. For the most part, as far as we currently know, most CSF finds its way from the cord back to the brain where it eventually flows into the major veins of the brain and exits the skull by way of the internal jugular and vertebral veins.
Click on the sketch of the brain below to enlarge it. (This is a sagittal view meaning looking at one half of the brain and cord as though they were split from front to back.) In this analogy the person is lying on their side. Now look at the sketch as though it was a nautical map of many lakes and rivers with the brain and cord being the land masses. All the folds, creases, crevices and cracks you see in the brain are like large and small fiords filled with water (CSF). The coast of the brain is completely surrounded by the sea so that no surface is untouched by water (CSF). The cord is, likewise, surrounded by water. Both are further bound by large rivers, which are the dural sinuses (veins) of the brain and vertebral veins of the cord.
CSF begins its journey in the lateral ventricles (lakes) located in the center of the brain. The squiggly lines surrounding the lakes are like mountains from which water flows down through streams to fill the lakes. The arrows show the direction of the current and CSF flow in the brain and cord.
The first two lakes flow into the next lake (third ventricle) where additional water from surrounding hills enter the system. It then flows through a tight canal called an aqueduct and enters yet another lake (fourth ventricle) with a large land mass protruding into it. Again, rivers from the surrounding hills that line the coast contribute even more water but this is the last place where water enters the system.
From the last lake (the fourth ventricle) CSF flows out into a gulf called the basal cisterns of the brain. From here, in the gulf, it can flow in one of two directions. It can either flow back up to the top of the brain or it can flow down into the cord. At the bottom of the cord is a large sea called the lumbar cistern. The capacity and volume of CSF (water) in the cord and lumbar cistern, like the ocean, is far greater than the combined capacity of all the ventricles, cisterns and spaces in the brain.
The direction CSF takes when it enters the gulf of the basal cisterns depends on which way the tide is going which is determined by the gravitational pull of the earth, as well as the time of day, which will be explained below. If it gets strong enough, wind can also affect the current and flow of CSF (water) in the cisterns (gulf). It can even cause it to take alternative routes. In either case, once it leaves the (ventricles) lakes where it is produced, CSF moves through channels that don’t contribute any additional water. Those channels are depicted by spaces with stipled lines.
In the position described above (the person on their side) the tide is in and the flow of CSF in the brain and the cord is mostly upwards toward the top of the brain. When it reaches the top of the brain it empties into part of the drainage system of the brain called the venous lacunae, lacunae means lakes. The venous lacunae contain canals called arachnoid granulations that are small protrusions (villi) of the arachnoid layer (middle covering of the brain) that connect the CSF pathways to the largest vein of the brain called the superior sagittal sinus. They transfer CSF back into the blood stream through the venous drainage system.
After it leaves the stipled CSF pathways and enters the superior sagittal sinus by way of the arachnoid granulation, slightly further down you can see a white circle called a confluence. A confluence is a place where rivers meet. In this case several large veins (rivers) meet at the confluence. From here the large veins drain down into the basement of the skull called the posterior fossa and enter into either the internal jugular veins or vertebral veins.
The tide changes in this analogy when we turn the system upright. When we stand upright, the current speeds up and the tide flows away from the brain. During the night when we sleep the tide returns back toward the brain. Hanging upside down (inversion) causes a strong reversal in the tide. Straining while holding the breath, which is called a Valsalva maneuver also causes back pressure against the current and can, likewise, reverse tides. Strong tides can cause rivers to change their course in the brain and seek other outlets. In my book, The Downside of Upright Posture, I discuss giraffes, bats and whales and the forces they have to deal with. Giraffes and bats had to find ways to contend with tides caused by exceptional inversion flows from long necks and spending long periods of time hanging upside down. In giraffes it occurs when they lower their head to drink water. In bats the tides shift when they sleep. In humans tides shift when we wake up from lying down to sit or stand upright.
The first place to feel the affects of shifts in currents and tides in the brain is where they collide in the gulf of the basal cisterns. If you look closely at the picture you will see a cistern above and below the cerebellum. There are also cisterns below and in front of the cord. The cisterns in the spaces above the pons of the cord and the cerebellum surround the midbrain. Among other things the midbrain contains the cerebral aqueduct (canal for CSF flow) and the substantia nigra. The substantia nigra is where dopamine is produced and is affected in Parkinson’s disease. I suspect that increased volume and pressure in the ventricles and cisterns may play a role in Parkinson’s disease. Increased CSF volume and pressure in the ventricles and cisterns may play a role in other neurodegenerative diseases as well.
The wind in the system comes from respiration (breathing). Most times breathing merely creates ripples that help to move CSF along. Sometimes, however, it causes a great deal of back pressure, such as in a Valsalva maneuver mentioned above, which forces CSF to find alternative outlets to exit the brain in order to keep things flowing and prevent backups in the system.
When it comes to the impact of currents, winds and tides, tide has a far greater influence on CSF flow. When large ocean tides rush into small river channels tidal bores (waves) occur. Where river currents and ocean tides collide standing waves called clapotis can occur. Tidal bores and clapotis (covered in my last blog) cause turbulance that moves depris which scour and undermine anything in its wake. Coasts are shaped by the relentless ebb and flow of daily tides. Anything that stands in its way or disrupts the ebb and flow of relentless tide and current is subject to erosion. The same thing happens in the brain.
When it comes to the brain the posterior fossa is the first area to feel the affect of tidal bores and clapotis. If the tidal waves are strong enough it can start to back up into the lakes (ventricles) and affect the structures that line their shores. The first ventricle (lake) to feel the affect is the fourth ventricle (lowest). Not surprisingly, the cisterns and ventricles are similarly affected in Dandy-Walker syndrome seen in children and a variant of Parkinson’s disease called multisystem atrophy or olivopontine cerebellar atrophy seen in adults. Both conditions are associated with enlarged cisterns and cystic (enlarged) fourth ventricles mentioned in previous posts.
Dandy-Walker sydrome is a congenital malformation of the brain originally referred to as Dandy-Walker cysts. It was named after Dr. Walter Edward Dandy and Dr. Earl Walker. The contributions of Dr. Dandy to neurosurgery and our understanding of CSF flow and hydrocephalus are legendary and far too numerous to describe here. Among other things he trained under Dr. Harvey Cushing mentioned above. The Dandy Walker cyst-like malformation is somewhat like a reverse Chiari malformation in that the posterior fossa is too large, the brainstem and cerebellum are too small and the cerebellum herniates upward into the tentorium cerebelli rather than downwards into the foramen magnum. Brain shrinkage and increased CSF volume has also been associated with Alzheimer’s disease and multiple sclerosis.
The choke point in the CSF and venous circulatory system of the brain is in the foramen magnum and upper cervical spinal canal. Degeneration (spondylosis) and misaligments of the lower cervical spine can further affect the current and flow of blood and CSF between the brain and cord. For additional information regarding the connection between the brain and cord visit our site at www.upright-health.com.