The ependyma is a cellular membrane that surrounds the ventricles of the brain and the spinal cord. It typically consists of ependymal cells that have hair-like projections called cilia, which can help move Cerebrospinal Fluid (CSF) throughout the spinal column and brain. There are also cells called tanycytes in the ependyma, which often connect to nerve cells and may help move various types of molecules to and from the brain. These cells can control pituitary gland functions and may also affect the synthesis of nitric oxide to control neurological activity and blood flow. Structures called microvilli in the membrane can absorb CSF.
Ependymal cells are linked to various small organs, including the choroid plexuses that secrete cerebrospinal fluid, and the area postrema, at the end of the fourth ventricle of the brain, which is usually dominated by microvilli. The ependyma is typically connected to a pineal gland responsible for melatonin secretion, the posterior pituitary gland, and other small organs in the brain. Also acting as a physical barrier, the membrane can also block potentially dangerous materials in the CSF from causing brain damage. It often filters out toxins before any molecules or fluids can pass through.
The filtration process is usually aided by enzymes that allow molecules to be transported. Toxins are blocked, and substances called amines, which include serotonin and dopamine, can be deactivated by an enzyme called monoamine oxidase located in the ependyma. Tanycytes that are connected to nerve fibers sometimes control pituitary hormone levels, and are often present in a part of the brain called the hypothalamus. There are also places in the ependyma where a substance that regulates water and electrolytes in the brain can bind to.
Some medical studies have suggested that there may be stem cells in the ependyma. Neural cells of this type are thought by some researchers to possibly restore hearing when they are implanted into the cochlea, and organ in the inner ear. Medical problems associated with the membrane can include inflammation, a tumor called an ependymoma, and a type of tumor that originates in the choroid plexuses.
The ependyma could also be involved in neurological recovery after an injury to the brain or other parts of the central nervous system. A substance called fibroblast growth factor may be regulated by the membrane’s cells and activated after trauma. Neurological activity, blood flow, and the ability of the nervous system to recover, therefore, are regulated by this protective layer of cells.