The ventricles of the brain (Lat. ventriculi cerebri) are a system of 4 interconnected cavities distributed throughout the deeper parts of the brain. Each ventricle is home to a choroid plexus – a brain structure responsible for the production of cerebrospinal fluid.
The two largest cavities are the lateral ventricles in the cerebrum, the third ventricle is located in the diencephalon of the forebrain (between the right and left thalamus), while the fourth ventricle is located at the back of the pons and in the upper half of the medulla oblongata.
The entire surface of the ventricular system is made up of an epithelial cell layer, labeled as an ependyma.
What Is Choroid Plexus?
The choroid plexus refers to a secretory tissue located in each of the 4 ventricles of the brain. It’s a network of capillaries and vitally important ependymal cells that are found in the walls and roofs of this ventricle system. These cells produce cerebrospinal fluid and transport it within the cranial cavity, i.e. the skull.
The choroid plexus has two major roles in the function of the body. Apart from the fact it’s in charge of the production of cerebrospinal fluid, it also provides the brain and other central nervous system tissue with a barrier from toxic matter.
Why Are the Ependymal Cells So Important?
The ependymal cells are a subtype of glial cells. They are responsible for the transport of electrolytes between the cerebrospinal fluid and the brain parenchyma, as well as for the maintenance of homeostasis in the brain and the formation of the blood-cerebrospinal fluid barrier.
However, their most important function is the production of the cerebrospinal fluid that is secreted into the ventricles of the brain.
What Is the Structure of the Ventricles of the Brain?
As we already mentioned, the ventricle system of the brain comprises of 4 elements:
- Left and right ventricle of the brain
- Third ventricle of the brain
- Fourth ventricle of the brain
In addition, these communicating cavities are interconnected with several foramina.
Left and Right (Lateral) Ventricles of the Brain
The left and right (lateral) ventricles are C-shaped structures located within both hemispheres of the cerebrum. They have structures in the form of “horns” that branch into the frontal, occipital, and temporal lobes, while the central part (the body) is located in the parietal lobe of the cerebral cortex:
- Body of the lateral ventricles
- Anterior (frontal) horn of the lateral ventricles
- Posterior (occipital) horn of the lateral ventricles
- Inferior (temporal) horn of the lateral ventricles
These lateral cavities, together with their interconnecting channels, comprise the cerebral ventricular system.
Third Ventricle of the Brain
The third ventricle is connected to the lateral ventricles by the foramen of Monro. The third ventricle is located right in the middle of the right and the left lobe of the thalamus. Also, there are 4 protrusions on the anterior surface of the ventricle:
- Supra-optic recess – located above the optic chiasm
- Infundibular recess – located above the optic stalk
- Infundibular recess – located above the pituitary infundibulum
- Pineal recess – protrudes into the pineal infundibulum
The floor of the third ventricle is made up of optic chiasma, the tuber cinereum and the infundibulum, the mamillary bodies, the posterior perforated substance, and the tegmentum of the midbrain, while its roof comprises of the ependyma that branches across the two lobes of the thalamus and the surface of the ventricular system of the brain.
Fourth Ventricle of the Brain
The fourth ventricle of the brain is a diamond-shaped cavity located in the brainstem. This ventricle has both a roof (composed of the cerebellum) and a floor (made up of the rhomboid fossa).
The upper part of the roof comprises the upper cerebellar peduncles and the medullary velum (a thin sheet of white matter). The lower part of the fourth ventricle’s roof is made of non-nervous tissue labeled as the inferior medullary velum.
The most characteristic feature of this brain cavity is, certainly, the rhomboid fossa – the floor of this ventricle. The rhomboid fossa can be divided into a left and right half by the median sulcus, and into an upper and lower triangle by the stria medullaris.
The Foramina of the Ventricular System of the Brain
The human skull contains numerous openings shaped like small holes, called foramina. There are 21 of these special holes on the human skull, serving as passages for the cranial nerves, blood vessels, and arteries of the face that further connect to the tissues of one part of the body to another.
There are 4 foramina that connect the ventricle system structures of the brain:
- Interventricular foramina (or: Foramina of Monro) – These channels connect the lateral ventricle to the third ventricle of the brain.
- Cerebral aqueduct (Sylvius) – The cerebral aqueduct is one of the most notable parts of the mesencephalon, since it provides a pathway for the cerebrospinal fluid to flow between the third and the fourth ventricle in the brain. This cerebral aqueduct is also known as the Sylvian Aqueduct, or The Aqueduct of Sylvius – named after the anatomist Franciscus Sylvius who first discovered it.
- Median aperture (or: Foramina of Magendie) – This foramina supports the flow of the cerebrospinal fluid from the fourth ventricle to the subarachnoid space in the brain.
- Right and left lateral aperture (or: Foramina of Luschka) – This paired structure connects the fourth ventricle to the subarachnoid space in the brain.
The Cerebrospinal Fluid and Its Function
What Is the Cerebrospinal Fluid?
The cerebrospinal fluid is a clear and colorless liquid which is renewed four to five times a day. The tissue of the brain floats in cerebrospinal fluid (CSF) within the skull. The fluid consists of water and other plasma components, amino acids, as well as glucose that provides nourishment to the brain tissue.
The cerebrospinal fluid protects and nourishes both the brain and spinal cord while it flows around them. It carries the proteins and glucose that provide energy for the proper function of the brain cells. It also contains lymphocytes that guard the brain structures against infection.
Where Is the Cerebrospinal Fluid Produced in the Brain?
The cerebrospinal fluid is produced by the choroid plexuses in the lateral ventricles and drains into the third ventricle. From there, it flows into the fourth ventricle, which is located in front of the cerebellum. The cerebral fluid is able to circulate in the brain via pulsations of the cerebral arteries.
What Are the Main Functions of the Cerebrospinal Fluid of the Brain?
The cerebrospinal fluid has 5 primary functions in the human brain:
- Protection – It protects both the brain and the spinal cord from trauma by cushioning the structures of the brain, thus limiting neural injuries.
- Buoyancy – The cerebrospinal fluid provides buoyancy and moisture to the brain and spinal cord.
- Chemical stability and nutrition – The cerebrospinal fluid both supplies nutrients to the tissues of the central nervous system and creates a functional environment so that the brain structures can perform their functions properly.
- Waste removal – The cerebrospinal fluid removes the waste products that result from the metabolism of the brain cells.
- Prevention of brain ischemia – By decreasing the flow of the cerebrospinal fluid within the skull, the pressure on the structures is relieved, and in that way, the CSF supports the prevention of brain ischemia.
How Does the Cerebrospinal Fluid Circulate in the Brain?
The circulation of the cerebrospinal fluid in the brain can be described in four steps:
- Site of fluid production (choroid plexuses) – The cerebrospinal fluid found in the ventricles in the brain is produced in clusters of thin-walled capillaries, known as choroid plexuses. These capillaries line the walls of the ventricles.
- Direction of flow – Fluid moves from the brain’s lateral ventricles into the third and fourth ventricles. The fluid then flows up the back of the brain, down around the spinal cord, and up to the front of the brain.
- Circulation around the spinal cord – The cerebrospinal fluid ebbs and flows around the spinal cord and through its central canal.
- Site of reabsorption (arachnoid granulations) – After circulating around the brain, the cerebrospinal fluid is reabsorbed into the blood via structures known as arachnoid granulations, which are projections of the arachnoid layer into the large sagittal sinus, or cerebral vein.
What Is the Function of the Ventricles of the Brain and Why Are They So Important?
Even though the brain is protected from external damage by the skull and, on the inside, wrapped in three meningeal layers – the dura mater, arachnoid mater, and pia mater, there still is some space left between the structures of the brain. Hence, this space is filled with the cerebrospinal fluid that is produced in the ventricular (hollow) system of the brain.
The ventricles of the brain are of vital importance to the normal functioning of the central nervous system and its structures. They protect the brain by cushioning it with the cerebrospinal fluid, thus protecting it from any head trauma that could lead to fatal consequences.
What Happens When the Ventricles of the Brain Become Dysfunctional?
Any damage to the ependymal cells that line the ventricles or a change in the flow and structure of the cerebrospinal fluid can lead to life-endangering medical conditions or diseases.
One of them is Hydrocephalus – a medical condition caused by the enlargement of the head due to a build-up of excess cerebrospinal fluid. It mostly occurs due to impaired circulation or absorption. The resulting medical condition can cause damage to the brain tissue due to the direct pressure the overfilled brain cavities cause.
Fun Facts
Did you know?
- The lateral (side) ventricles are the largest cavities in the human brain. There is one lateral ventricle in each of the brain’s hemispheres.
- The ventricular system is derived from the lumen of the neural tube.
- Buoyancy is the force that the cerebrospinal fluid exerts on the structures of the brain that are wholly or partly immersed in it. There are three types of buoyancy – positive, negative, and neutral.
- Positive buoyancy occurs when an object happens to be lighter than the fluid that opposes its weight. Therefore, the object will float. This is because the buoyant force is greater than the weight of the object.
- Negative buoyancy occurs when an object happens to be denser than the fluid displaced by it. Here the object will sink because its weight happens to be greater than the buoyant force.
- Neutral buoyancy occurs when the weight of an object is equal to the fluid it displaces. A good example of this are scuba divers. Namely, a scuba diver is skilled in techniques to regulate buoyancy underwater.
- Buoyancy is also called the Archimedes principle, after the Greek mathematician Archimedes who discovered it.
- The cerebrospinal fluid also plays a vital role in the autoregulation of cerebral blood flow.
- Ischemia occurs when the structures of the brain do not receive a sufficient supply of oxygen in order to keep the cellular metabolism functional. This can result in severe damage to the tissues of the brain.
- The foramina of the skull are of great importance because of the fact that many of the most important blood vessels and nerves pass through them in order to both supply the brain and to carry information to and from the brain, which is a highly complex process.