Brain ventricles perform several functions that help keep the central nervous system healthy. Learn how these processes interact to produce a stable environment where your brain can function properly. Then, review these concepts with a quiz.
Definition of Brain Ventricles
If you’re like most people, you probably have not thought of your brain as an organ that floats in a bag of fluid. But in fact, your entire central nervous system (CNS), which consists of the brain and spinal cord, is suspended in this way.
Why? Where does the fluid come from, and what do ventricles have to do with it?First, let’s take a look at the larger picture, because it will help create an understanding of why the brain ventricles are so important. By definition, a ventricle is a hollow area or cavity within an organ, usually filled with some kind of fluid. For example, the heart has two ventricles that fill with blood, which is pumped throughout the body. Brain ventricles are similar but without the pumping action. Instead of blood, they are filled with cerebrospinal fluid (CSF), which is a clear fluid that has several functions in the CNS, including creating the blood-brain barrier as a cushion for the brain against the skull and a layer of protection against diseases and infections, toxins, and some drugs. We’ll cover CSF’s functions in more detail later.Together with the fluid, the ventricles are an intricate part of a unique and much larger system that provides nutrients and other vital substances to nerve cells.
This is because the brain is composed of specialized and delicate tissue found nowhere else in the body. Therefore, it’s susceptible to chemical and physical injury, and its maintenance and protection is paramount. The figures here demonstrate how such a complex system is organized and detail the many parts involved.
The Ventricular System
Within the brain there are four ventricles: two lateral (meaning away from the midline of the body), a third ventricle near the center of the brain, and the fourth ventricle under the cerebellum. They are all connected by smaller passageways that allow the CSF to circulate slowly among them.
This labyrinth is called the ventricular system. However, the CSF it contains also travels through the central canal located inside the spinal cord and also around the outside of the cord all the way to your tail bone. The CSF then circulates back up to the brain. The net result is that your CNS is floating in fluid within a bag of fibrous tissue called the dura mater. It’s the thickest of several membranes known as the meninges that cover the CNS.
Focus on Fluids
So where does this fluid come from? Your blood.
Inside each ventricle is a network of small blood vessels called the choroid plexus. Scientists refer to a branching network of vessels or nerves as a plexus; in this case, a choroid or blood-related plexus. It continually produces CSF by extracting the basic ingredients from the circulatory system.
Blood plasma, the clear fluid component of blood, is filtered through the cells of the choroid plexus, and it collects in the ventricles. The filtering process is specific and only allows certain items to pass through, such as particular proteins and gases, water, and some nutrient-rich material. The filtration action also helps to form the blood-brain barrier that protects the CNS from bacterial infections, toxins, and some drugs. This is the same concept as using a filter to make your coffee in the morning. The fluid you want gets through but the grinds stay behind.If CSF is constantly being produced, how does it leave the system so that the ventricles don’t become swollen with fluid and damage brain tissue? This can happen when things go wrong and the brain ventricles do become swollen, a condition known as hydrocephalus.
In another layer of the meninges called the arachnoid mater, named after its spiderweb-like appearance, are areas called arachnoid granulations. These sites allow the CSF to flow back into the bloodstream, like a one-way flood gate, thus controlling the fluid pressure within the ventricular system. As a whole, the brain ventricles and CSF integrate into a process that provides several functions to help meet the needs of the CNS.
Ventricular System Functions
Let’s take a look at some of these needs.1.
Shock AbsorptionThe total volume of CSF that the brain ventricles create helps to reduce or prevent damage from an external blow, by absorbing and dissipating the energy. For example, as CSF on the outside of the CNS absorbs the initial shock, fluid within the ventricles and spinal cord pushes outward and prevents these structures from collapsing.2. Reduce Physical StressImagine yourself floating in a pool.
Your muscles relax and those in your neck no longer have to work very hard to support your head in an upright position. On land, your skull is pushing downward onto your vertebrae, which respond by supporting this heavy load. The brain does the same thing; however, it is composed of very delicate tissue. By floating in a bag of fluid, the brain’s weight is partially neutralized so that it doesn’t press directly on the skull and cause tissue damage.
3. Provide Chemical BalanceThe CSF is actually a sea of selected chemical substances that contains hormones, nutrients, electrolytes, and waste products. Hormones are used for brain development and physical maintenance, the electrolytes provide necessary ions for the proper production of nerve impulses, and nutrients keep the nerve cells alive. Therefore, the cells produce waste products that enter the CSF. Because the fluid circulates in only one direction, the wastes are eventually removed via the arachnoid granulations.
As you can see, the brain ventricles are more than just holes in your head.
While they are indeed hollow areas or cavities within an organ, usually filled with some kind of fluid, they actually produce the fluid the entire central nervous system (CNS) (the brain and spinal cord) floats in for protection, and the bag of meningeal layers reabsorbs it. This fluid is cerebrospinal fluid (CSF), which is a clear fluid that has several functions in the CNS, including creating the blood-brain barrier as a cushion for the brain against the skull and a layer of protection against diseases and infections, toxins, and some drugs. The ventricles make up the ventricular system, which is made up of four separate brain vesicles that create a labyrinth of interconnected passageways.
The choroid plexus (a network of small blood vessels) is what produces the CSF, the dura mater (a bag of fibrous tissue) is what cushions the CSF in place, while the meninges (the thickest of several membranes) cover the whole thing. Finally, the arachnoid granulations are sites that allow the CSF to flow back into the bloodstream, like a one-way flood gate, thus controlling the fluid pressure within the ventricular system. This is basically part of a conveyor belt of CSF that supplies nerve cells with their required nutrients and simultaneously removes waste products.
Therefore, the ventricular system works in conjunction with other body parts to create mechanisms that ensure the CNS receives proper care and maintenance through chemical balance, shock absorption, and physical stress reduction on the brain.
Brain Ventricles Review
|There are four brain ventricles – two located on the sides of the brain, one near the center, and one under the cerebellum – that compose the ventricular system|
|Brain ventricles are hollow tubes filled with cerebrospinal fluid (CSF) that produce all the CSF for the entire central nervous system|
|The brain ventricles have multiple functions: *Provide shock absorption for the brain *Reduce the physical stress on the brain *Help the brain maintain a chemical balance|
When you are finished, you should be able to:
- Define ventricle and cerebrospinal fluid
- Recall where the brain ventricles are located and how many there are
- Summarize the roles of the brain ventricles
- List the functions of the cerebrospinal fluid and explain where it comes from
- Describe how the CSF is kept in balance
- Examine the needs of the CNS that the ventricular system works to meet