Since the time they were originally characterized, glial cells have been viewed as a class of cells whose role is to essentially do little more than provide support for neurons in the nervous system. In fact, the name "glia" actually derives from the Greek word for glue. These cells have mostly been viewed as the glue for the brain, but this view has changed significantly in the last 10 or more years.
Glial Cells in the Nervous System
Most people know about the presence of nerve cells, or neurons, in the brain. However, most people are unaware of the presence of an entirely different group of cells in the nervous system, the glia. In the central nervous system (the brain and spinal cord), the glia consist of three different types of cells: astrocytes, oligodendrocytes, and microglia. In the peripheral nervous system (the nerves that are found in the rest of your body) there is a different type of glial cell known as a Schwann cell.
Perhaps the most commonly thought of function for glial cells is the production of myelin. This fatty insulation is wrapped around a significant number of nerves, but not all, and allows for a dramatic enhancement in the speed of signals along the cell membrane through the process known as saltatory conduction. In the central nervous system, oligodendrocytes produce the myelin sheaths that wrap up the axons of nerve cells and leads to one of the clearly distinctive structures of the brain, white matter. And, of course, the myelin made by oligodendrocytes is the target of the disabling disorder multiple sclerosis (MS). In the peripheral nervous system, a subclass of the Schwann cells that are present are responsible for producing the myelin that wraps some of the peripheral nerves.
Immune Function of Glial Cells
One of the types of glial cells in the central nervous system is known as microglia. These specialized glial cells are the defenders of the central nervous system. They are recruited to sites of injury and are responsible for hunting down offending invading organisms and destroying them before they can cause any significant damage to the brain. This is a very important function since the brain is known to be"immune-privileged", that is it is not accessible by the bulk of the immune system that works in the rest of the body. This is due to the presence of the "blood-brain barrier".
Glia and Brain Function
Over the last decade or more, it has become increasingly apparent that glial cells do more than either simply produce myelin or "keep neurons happy". Glial cells are apparently critical players in the establishment of normal brain function and the maintenance of important brain circuits. Nowhere has this involvement been more studied than in the setting of schizophrenia. Numerous studies have now suggested that alterations in oligodendrocytes, and the white matter they are involved in generating, could be components in the development of selected neuropsychiatric disorders. Specialized magnetic resonance imaging studies of the brain have suggested that white matter regions in select parts of the brain are changed in people suffering from certain psychiatric conditions (Fields RD).
Perhaps the most interesting and intriguing change in understanding relating to the function of glial cells in the nervous system comes from studies over the last decade indicating that astrocytes in the brain participate in neural signaling networks. Astrocytes express neurotransmitter receptors, and indeed they themselves can release neurotransmitters. There is a growing agreement that astrocytes play an important role in both stabilizing and regulating synaptic circuits in the brain (Butt AM).
Research continues to point towards an important and growing role for glial cells in not only the development of the nervous system but also in its maintenance and synaptic communication. Pretty remarkable for a class of cells that were originally heralded for being sort of like glue.
To learn more about causes and treatments for schizophrenia, visit the schizophrenia pages at the Brain and Behavior Research Foundation (BBR Foundation) and at the US National Institute of Mental Health (NIMH).
Reference:
Fields, RD; White matter in learning, cognition and psychiatric disorders. Trends Neurosci. 2008 Jul;31(7):361-70.
Butt AM; ATP: a ubiquitous gliotransmitter integrating neuron-glial networks. Semin Cell Dev Biol. 2011 Apr;22(2):205-13.
Kenneth Rosen - I am a medical research doctor with more than 20 years of experience studying how the nervous system and skeletal muscle develop and ...
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