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Glial cells, or glia, are specialized cells found throughout the nervous system to support its functions. Historically they were not heavily studied because researchers were more interested in neurons, believing that glial cells acted primarily like mortar to hold the nervous system together. Research in the 1960s began to reveal that these cells actually played a number of important roles, including the ability to signal to each other and control signaling with other cells. Studies on their function are important for understanding how the nervous system works and recovers from injury.
One role of the glial cell is one of an insulator. A specific subtype known as the oligodendrocyte produces myelin, which protects neurons from each other and regulates the movement of signals. Glial cells like astrocytes offer structural support to hold neurons in position and also provide a supply of food and cleanup. As neurons produce waste, the surrounding cells remove it for processing. Other glial cells known as microglia can attack invading organisms and engulf dead neurons for removal.
Researchers working with neurons must cultivate glia alongside them to provide the necessary support. Otherwise, the neurons cannot survive in culture. The exact balance of numbers between glial cells and neurons is a subject of discussion; originally it was believed to be around nine to one, but other research suggests there may be more neurons present than originally believed by researchers attempting to count them. More glial cells than neurons are present overall in the nervous system, even if the precise number is uncertain.
Microglia arise from the bone marrow and are continually renewed throughout life. Other cells develop from the neural tube and crest, the same structures that give rise to the rest of the nervous system. They are distributed throughout the central and peripheral nervous system to provide support for a variety of functions. Regulating their environment is one of their most important tasks, making it possible for complex neurological signals to pass through the neurons.
Disorders can arise in the glial cells. These can include cancers, where cells start to reproduce out of control. Astrocytoma, for example, is a cancer arising in the astrocytes which occurs when a cell’s normal control mechanisms shut down and it keeps dividing and growing. Treating these conditions can be complex, as it may require surgery and other therapies in delicate areas of the brain, which could expose patients to risks like brain damage that leads to cognitive impairments.