Our pink-grey brain looks like a continuous strand of thin sausages folded up so it would fit into our skull. But amongst the two spheres of "grey matter" are these hollow cavities. From the side, these cavities look like the creatures Ellen Ripley battles in the Alien movies. Nor does it appear a lot of thinking goes on in these spaces. Yet, the ventricles of the brain do serve a vital purpose.
The ventricles of the brain are the cavities making up the ventricular system. The four cavities contain and produce cerebrospinal fluid (CSF). CSF has four main functions: structural support, protecting the brain, transporting nutrients to the nervous system tissue, and removing waste and toxins.
It's common to think of the skull as an aquarium where our brain floats, all happy and warm, as it serves its role as our supercomputer. People make jokes about humans not really needing their bodies, "Just stick my brain in a jar of water." But that "water" does more than keep our brains moist, and in order to serve its vital purpose, it depends on the ventricular system.
What Are Ventricles?
The ventricular system comprises of four cavities amongst the brain:
- Right lateral ventricle
- Left lateral ventricle
- Third ventricle
- Fourth ventricle
These cavities have a membrane lining known as the choroid plexus, making our essential cerebrospinal fluid (CSF).
The cells of the choroid plexus are ependymal, a type of glial cell. Glial cells are often referred to as the nervous system's "glue" or the brain's "white matter." However, glial cells are actually essential support for neurons. Without the glial cells, the ventricles could not perform their vital roles.
What Are The Ventricles Main Role?
The ventricles' primary roles are:
- Producing cerebrospinal fluid
- Distribution and circulation of the cerebrospinal fluid
So for those that think of the skull as an aquarium, imagine it as having an incredibly fancy filtration and support system. This filtration system is our ventricular system, making a nutritious liquid, circulating it, and cleaning itself.
What Are The Four Ventricles Of The Brain?
As stated above, there are four ventricles of the brain:
- Right lateral ventricle
- Left lateral ventricle
- Third ventricle
- Fourth ventricle
These four ventricles work together in separate areas of the brain, making and transporting cerebrospinal fluid around the inside of the skull and spine. The first two ventricles feed into the third, which funnels into the fourth that eventually drains into the spinal cord.
The Right & Left Lateral Ventricles Of The Brain
The first two ventricles are essentially mirror images of each other. These are shaped like the profile of a sock puppet's mouth, making a "c" (ready to bite the other socket puppet). These aggressive Cs are positioned on each side of the cerebral cortex, which we recognize by its folded sausage-like structure. The walls of the lateral ventricles are made of the choroid plexus, as are the roofs of the third and fourth.
The C has three horns that extend into the lobes of the brain: frontal, occipital, and temporal. The interventricular foramen is an opening near the brain's center, between the two hemispheres. This opening, also known as the foramen of Monro, connects the lateral ventricles to the third ventricle.
The Third Ventricle Of The Brain
The third ventricle is much smaller than the first two. This narrow ventricle is positioned on the diencephalon, between the right and left lateral ventricles. It is an odd, funnel-like cavity, often described as a "misshaped donut." It links to the fourth ventricle via the cerebral aqueduct.
The "hole" of the misshaped Danish is known as the interthalamic adhesion, which forms the wall of the third ventricle. It is pretty tiny, around a centimeter long. Despite its minute size, it is a subject of great debate, including if it should be classified as gray commissure or white commissure. More intriguing is that 20% of people don't seem to have one and are no worse off for its absence.
The Fourth Ventricle Of The Brain
The fourth ventricle is low down in the back of the skull, between the cerebellum and the brainstem. From a certain angle, this ventricle looks like a kite. It produces the least CSF of the four ventricles.
CSF in the fourth ventricle is drained into the central spinal canal and the subarachnoid cisterns. The central spinal canal keeps the spinal cord full of essential CSF. The subarachnoid cisterns ensure the brain is kept "floating" in CSF.
What Are The Four Main Functions of Cerebrospinal Fluid?
Cerebrospinal fluid (CSF) is essential to our brain and spinal cord. Each full-grown person has around 90 to 200 ml of CSF circulating in their body. Thanks to this circulation, our brains and spine are kept at a stable temperature.
Cerebrospinal fluid is not recycled through the ventricles like the heart takes in and pumps out blood. Instead, the ventricles are continuously making cerebrospinal fluid, distributing it, where it eventually is disposed of. The average adult ventricle system produces 20ml of CSF per hour.
The four main functions of cerebrospinal fluid are:
- Acting as a support structure for the brain
- Acting as a protective shock absorber for the brain and spinal cord
- Supplying nutrients to the nervous system tissue
- Acting as a waste removal system
Cerebrospinal Fluid Is The Brain's Structural Support
The cerebrospinal fluid acts as liquid structural support to the brain. With all that CSF creating an aquarium of our skulls, the brain is buoyant. The suspended state cushions the brain from the stress gravity puts on it. Thus, CSF is essentially protecting the brain from gravity. The support is significant; for example, a 1500g brain only "weighs" 50g when suspended in CSF.
Without CSF, the brain's weight and pull from gravity can cause it to lose its shape. The pulling and stretching can then lead to tragic tearing. This is partly why when people suffer a CSF leak, there is fear of damage to the brain, even if the person hasn't received direct trauma to the head.
Cerebrospinal Fluid Is The Brain's Shock Absorption
Your brain is the most essential organ to a person's existence. People have successfully lived on after having a new heart or lung transported into their body, but the brain is vital to keeping them going. Thus, your body protects your brain with a hard bone: the skull.
The problem is that the solid walls of the skull are dangerous for the delicate organ. Thus, the cerebrospinal fluid surrounds the brain and will act as a shock absorber if you knock your head. It isn't perfect. A nasty fall or a horrible car crash can still result in the brain hitting the skull, causing injury and life-threatening swelling. But without the cerebrospinal fluid, even a seemingly minor knock could be disastrous.
Cerebrospinal Fluid Is The Brain's Food Supply Chain
Cerebrospinal fluid is more than water. It is a nutrient-rich liquid composed of substances such as glucose, proteins, lipids, and electrolytes. As the brain's ventricles produce and distribute the CSF, the fluid bathes the brain and spinal cord, bringing them all these essential nutrients to function and be healthy.
Cerebrospinal Fluid Is The Brain's Waste Removal System
The human body has its own sewer and dumpster systems to ensure there isn't deadly or disease-causing buildup of unnecessary matter and toxins. Cerebrospinal fluid plays a vital role in the body's waste management system.
As the CSF travels around the brain and spinal column, dropping off nutrients, it is also "picking up the trash." The proverbial trash is produced by nerve cells that release toxins and by-products. When the CSF eventually empties into the bloodstream, it takes the "trash" with it. These toxins and waste products are then carried to the body's "processing plants," such as the kidneys.
Can Cerebrospinal Fluid Be Blocked Or Leak?
Cerebrospinal fluid (CSF) can be blocked or leak out of the body, and this can cause life-threatening issues. Many problems result from the body having no regulating mechanism for the production of CSF. The body keeps making it at the same rate no matter what has happened. Thus, if there is a blockage in the drainage system, pressure will build up as CSF continues to be produced.
In small children, this phenomenon is often seen in the condition commonly known as "water on the brain." Unlike older kids and adults, these very young children have a skull that hasn't fully hardened. Thus, the child's actual head will swell with the growing buildup of CSF.
These blockages are often from trauma, such as a brain bleed blocking a passage in the ventricles. However, disease can cause blockages as well. One of the most famous is meningitis. As the disease causes inflammation in the meninges membranes, blockages can arise, which will go on to cause a condition called hydrocephalus.
Cerebrospinal fluid can also leak from the spine or cranium. Leaks are not common, but they can occur through trauma or as an unfortunate side-effect from a medical procedure like a lumbar puncture. A spinal leak isn't always life-threatening. Sometimes it only causes a headache, and a person needs to rest without further treatment as the body gradually rebuilds supply.
But other times, a leak can have grave consequences, resulting in debilitating conditions like memory loss. A CSF leak can also result in infection or disease, such as meningitis.
History Of Our Knowledge Of the Ventricles
Humans have known about the ventricles for a long time, but their beliefs were not always scientifically accurate. For example, the Ancient Greeks considered them "psychic pneuma." The "pneuma" wasn't in one part of the body, but many, and they were thought to be behind many of the roles our autonomic nervous system carries out, such as breathing.
The pneuma was often believed to be able to do these functions due to their connections to the soul or spirit. Take Plato, who split the pneuma into levels, where we first inhaled air from God. Then, the natural spirit of the veins would become the vital spirit when it entered the heart. But the highest form of pneuma was the "hollow" ones in our heads, and this was where the animal spirit dwelled. It was this spirit that was our essence of life.
The ancient Egyptians were also aware of cerebrospinal fluid, although not necessarily knowledgeable of why it existed. However, there are accounts from that time of the skull filling up with the liquid.
Leonardo da Vinci, who lived between 1542 and 1519, was fascinated by the ventricular system. He even made a model of it by injecting hot, liquid wax into the system by way of the fourth ventricle. Once the wax had hardened, da Vinci would remove the surrounding brain tissue, thus, creating a cast.
However, da Vinci did not put together that it was responsible for making cerebrospinal fluid. In fact, many presumed the ventricles were gaseous caverns.
It was Andreas Vesalius in 1543 that identified that the ventricles held liquid rather than gas. His insights slowly pushed out theories of gas and "spirits." But his work didn't lead him to discover the complete picture of the ventricular system. It would take nearly a century later until Thomas Willis proposed that CFS was made in the choroid plexus.
However, Willis' discovery didn't do away with people's attempts to connect the brain to spirits. René Descartes, for example, believed in the fluid of the brain ventricles. However, he argued that its flow was distributing spirits. He also thought the brain worked similar to the heart, pumping the fluids around.
But as much as it is fun to laugh at these older theories, the truth is that science has yet to fully unravel all the mysteries surrounding CFS. For example, scientists are trying to decide how much CSF influences the mind's functionality. One study found that young cerebrospinal fluid improved the memories of older mice. However, what this means for our future health and cognitive function as humans age remains to be seen.
Conclusion
The brain's four ventricles are responsible for the production of cerebrospinal fluid and its distribution. CSF is vital to our brains and spinal health, including protection, nourishment, and ridding it of toxins and buildup. However, the role of CSF continues to be studied and debated as many questions remain.
Resources
https://emedicine.medscape.com/article/1923254-overview
https://www.ncbi.nlm.nih.gov/books/NBK532932/
https://www.labce.com/spg1995235_three_main_functions_of_csf.aspx
