Ependymal cells are a specialized type of glial cell that originates from a layer of embryonic tissue called the neuroectoderm. They are a type of neuroepithelial tissue, functioning as a lining within the nervous system. Their primary functions are directly related to the fluid-filled cavities of the brain and spinal cord.
Location and Structure of Ependymal Cells
Ependymal cells form the delicate lining of the ventricles in the brain and the central canal of the spinal cord. This single-cell-thick layer, known as the ependyma, acts as a boundary between the cerebrospinal fluid and the brain tissue. These cells are typically simple cuboidal or columnar in shape, allowing them to fit together tightly.
The surface of these cells facing the fluid, called the apical side, is covered with two important structures: cilia and microvilli. Cilia are tiny, hair-like projections that can move, while microvilli are smaller, finger-like projections that increase the cell’s surface area. On their opposite side, the basal surface, ependymal cells have tentacle-like extensions that connect to other supportive brain cells called astrocytes, anchoring them within the nervous tissue.
Cerebrospinal Fluid Regulation
A primary responsibility of ependymal cells is managing cerebrospinal fluid (CSF). A specialized population of these cells helps form a structure called the choroid plexus, found within the brain’s ventricles. The choroid plexus is a network of blood vessels and a modified ependymal layer where cells take up water and molecules from the blood and secrete them into the ventricles as new CSF.
Once produced, the CSF must be circulated throughout the central nervous system. This movement is driven by the coordinated, rhythmic beating of the cilia on the ependymal cells’ surfaces. This constant motion helps to distribute nutrients and chemical messengers within the fluid and aids in flushing away waste products from the brain tissue.
Ependymal cells also contribute to forming a protective barrier. In the choroid plexus, the ependymal cells are connected by tight junctions, which limit the uncontrolled passage of substances. This creates the blood-CSF barrier, which meticulously regulates which molecules can move from the bloodstream into the cerebrospinal fluid, protecting the brain from harmful substances.
Role as Neural Stem Cells
Beyond their duties in fluid management, some ependymal cells can act as neural stem cells. Ependymal cells in specific regions, such as the forebrain, can be activated following an injury like a stroke. These cells can then serve as a reservoir to divide and generate new brain cells, a process called neuroregeneration.
This stem cell population can differentiate into various cell types, including new neurons and other glial cells. While they do not self-renew indefinitely, their existence points to a natural mechanism for brain repair. This capacity has made ependymal cells a focus of research, with scientists exploring how to harness this potential for new treatments for brain injuries and neurodegenerative diseases.
Connection to Neurological Conditions
The function of ependymal cells is so central to health that their dysfunction is linked to several neurological conditions. Tumors known as ependymomas can arise directly from these cells. These growths may obstruct the flow of cerebrospinal fluid, leading to serious complications depending on their location.
Damage to the ependymal lining can impair CSF circulation, leading to a condition called hydrocephalus. This disorder is characterized by an excessive accumulation of CSF within the ventricles, which increases pressure inside the skull and can cause brain damage. Obstruction of fluid pathways or problems with the cilia can contribute to this buildup.
Ependymal cells are also involved in the body’s response to inflammation in the central nervous system. In diseases like multiple sclerosis, these cells can be affected by the inflammatory process. Alterations in their function and integrity can contribute to the broader pathology seen in such conditions.