Ventricular System of the Brain

The ventricular system is a series of connecting hollow spaces called ventricles in the brain that are filled with cerebrospinal fluid. The ventricular system consists of two lateral ventricles, the third ventricle, and the fourth ventricle. The cerebral ventricles are connected by small pores called foramina, as well as by larger channels. The interventricular foramina or foramina of Monro connect the lateral ventricles to the third ventricle. The third ventricle is connected to the fourth ventricle by a canal called the Aqueduct of Sylvius or cerebral aqueduct. The fourth ventricle extends to become the central canal, which is also filled with cerebrospinal fluid and encases the spinal cord. Cerebral ventricles provide a pathway for the circulation of cerebrospinal fluid throughout the central nervous system. This essential fluid protects the brain and spinal cord from trauma and provides nutrients for central nervous system structures. Lateral Ventricles The lateral ventricles consist of a left and right ventricle, with one ventricle positioned in each hemisphere of the cerebrum. They are the largest of the ventricles and have extensions that resemble horns. The lateral ventricles extend through all four cerebral cortex lobes, with the central area of each ventricle being located in the parietal lobes. Each lateral ventricle is connected to the third ventricle by channels called interventricular foramina. Third Ventricle The third ventricle is located in the middle of the diencephalon, between the left and right thalamus. Part of the choroid plexus known as the tela chorioidea sits above the third ventricle. The choroid plexus produces cerebrospinal fluid. Interventricular foramina channels between the lateral and third ventricles allow cerebrospinal fluid to flow from the lateral ventricles to the third ventricle. The third ventricle is connected to the fourth ventricle by the cerebral aqueduct, which extends through the midbrain. Fourth Ventricle The fourth ventricle is located in the brainstem, posterior to the pons and medulla oblongata. The fourth ventricle is continuous with the cerebral aqueduct and the central canal of the spinal cord. This ventricle also connects with the subarachnoid space. The subarachnoid space is the space between the arachnoid matter and the pia mater of the meninges. The meninges  is a layered membrane that covers and protects the brain and spinal cord. The meninges consists of an outer layer (dura mater), a middle layer (arachnoid mater) and an inner layer (pia mater). Connections of the fourth ventricle with the central canal and subarachnoid space allow cerebrospinal fluid to circulate through the central nervous system. Cerebrospinal Fluid Cerebrospinal fluid is a clear aqueous substance that is produce by the choroid plexus. The choroid plexus is a network of capillaries and specialized epithelial tissue called ependyma. It is found in the pia mater membrane of the meninges. Ciliated ependyma lines the cerebral ventricles and central canal. Cerebrospinal fluid is produced as ependymal cells filter fluid from the blood. In addition to producing cerebrospinal fluid, the choroid plexus (along with the arachnoid membrane) acts as a barrier between the blood and the cerebrospinal fluid. This blood–cerebrospinal fluid barrier serves to protect the brain from harmful substances in the blood. The choroid plexus continually produces cerebrospinal fluid, which is ultimately reabsorbed into the venous system by membrane projections from the arachnoid mater that extend from the subarachnoid space into the dura mater. Cerebrospinal fluid is produced and reabsorbed at nearly the same rate to prevent pressure within the ventricular system from getting too high. Cerebrospinal fluid fills the cavities of the cerebral ventricles, the central canal of the spinal cord, and the subarachnoid space. The flow of cerebrospinal fluid goes from the lateral ventricles to the third ventricle via the interventricular foramina. From the third ventricle, the fluid flows to the fourth ventricle by way of the cerebral aqueduct. The fluid then flows from the fourth ventricle to the central canal and the subarachnoid space. The movement of cerebrospinal fluid is a result of hydrostatic pressure, cilia movement in ependymal cells, and artery pulsations. Ventricular System Diseases Hydrocephalus and ventriculitis are two conditions that prevent the ventricular system from functioning normally. Hydrocephalus results from the excess accumulation of cerebrospinal fluid in the brain. The excess fluid causes the ventricles to widen. This fluid accumulation puts pressure on the brain. Cerebrospinal fluid can accumulate in the ventricles if the ventricles become blocked or if connecting passages, such as the cerebral aqueduct, become narrow. Ventriculitis is inflammation of the brain ventricles that typically results from an infection. The infection can be caused by a number of different bacteria and viruses. Ventriculitis is most commonly seen in individuals who have had invasive brain surgery. Sources: Purves, Dale. â€Å"The Ventricular System.† Neuroscience. 2nd edition., U.S. National Library of Medicine, 1 Jan. 1970, www.ncbi.nlm.nih.gov/books/NBK11083/.The Editors of Encyclopà ¦dia Britannica. â€Å"Cerebrospinal fluid.† Encyclopà ¦dia Britannica, Encyclopà ¦dia Britannica, inc., 17 Nov. 2017, www.britannica.com/science/cerebrospinal-fluid.