Neuroglia Cells |
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| In this image, you see one large neuron, and a variety of glial cells. |
Glial cells have been a bit of a mystery in some ways. There was a time when they were thought to be simply a form of insulation, but not any longer. We now that there are many different forms of glial cells, and that they serve a variety of functions.
Here is a brief primer on glial cells from Wikipedia:
And now the podcast, in which we learn what is new in this area of research.Glial cells, commonly called neuroglia or simply glia (Greek for "glue"), are non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for the brain's neurons. In the human brain, there is roughly one glia for every neuron with a ratio of about two neurons for every three glia in the cerebral gray matter.[1]
As the Greek name implies, glia are commonly known as the glue of the nervous system; however, this is not fully accurate. The four main functions of glial cells are:
1. to surround neurons and hold them in place
2. to supply nutrients and oxygen to neurons
3. to insulate one neuron from another
4. to destroy pathogens and remove dead neurons.
They also modulate neurotransmission.[2]
Some glial cells function primarily as the physical support for neurons. Others regulate the internal environment of the brain, especially the fluid surrounding neurons and their synapses, and nutrify neurons. During early embryogeny, glial cells direct the migration of neurons and produce molecules that modify the growth of axons and dendrites. Recent research indicates that glial cells of the hippocampus and cerebellum participate in synaptic transmission, regulate the clearance of neurotransmitters from the synaptic cleft, release factors such as ATP, which modulate presynaptic function, and even release neurotransmitters themselves. Unlike the neuron, which is, in general, considered permanently post-mitotic[3], glial cells are capable of mitosis.
In the past, glia had been considered to lack certain features of neurons. For example, glial cells were not believed to have chemical synapses or to release neurotransmitters. They were considered to be the passive bystanders of neural transmission. However, recent studies have shown this to be untrue. For example, astrocytes are crucial in clearance of neurotransmitter from within the synaptic cleft, which provides distinction between arrival of action potentials and prevents toxic build-up of certain neurotransmitters such as glutamate (excitotoxicity). It is also thought that glia play a role in Alzheimer's disease. Furthermore, at least in vitro, astrocytes can release neurotransmitter glutamate in response to certain stimulation. Another unique type of glial cell, the oligodendrocyte precursor cells or OPCs, have very well-defined and functional synapses from at least two major groups of neurons. The only notable differences between neurons and glial cells are neurons' possession of axons and dendrites, and capacity to generate action potentials.
Glia ought not to be regarded as 'glue' in the nervous system as the name implies; rather, they are more of a partner to neurons. They are also crucial in the development of the nervous system and in processes such as synaptic plasticity and synaptogenesis. Glia has a role in the regulation of repair of neurons after injury. In the CNS, glia suppresses repair. Glial cells known as astrocytes enlarge and proliferate to form a scar and produce inhibitory molecules that inhibit regrowth of a damaged or severed axon. In the PNS, glial cells known as Schwann cells promote repair. After axonal injury, Schwann cells regress to an earlier developmental state to encourage regrowth of the axon. This difference between PNS and CNS raises hopes for the regeneration of nervous tissue in the CNS. For example a spinal cord may be able to be repaired following injury or severance.
Exploring Glial Cells with R. Douglas Fields
Posted on May 12th, 2010 by Ginger Campbell, MD
Recent research has discovered that glial cells (the non-neuronal cells that make up about 85% of the cells in the human nervous system) actually do more than just support neurons. In Episode 69 of the Brain Science Podcast I explore some of these recent discoveries with pioneering researcher, R. Douglas Fields, PhD. Dr. Fields is the author of The Other Brain: From Dementia to Schizophrenia, How New Discoveries about the Brain Are Revolutionizing Medicine and Science. The Other Brain provides a compelling introduction to this exciting new field. It is aimed at general readers, but it should also be on the must-read list for all students of neuroscience.
Episode Transcript (Download free PDF)
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References:
- The Other Brain: From Dementia to Schizophrenia, How New Discoveries about the Brain Are Revolutionizing Medicine and Science by R. Douglas Fields (2010)
- Glial Neurobiology: A Textbook by Alexei Verkhratsky and Arthur Butt (2007)
- Bullock, T. H., Bennett, M. V., Johnston, D., Josephson, R., Marder, E., Fields, R. D. “Neuroscience. The neuron doctrine, redux.” Science 310. 5749 (2005): 791-3.
Perspectives- Bullock, T. H. (2004) The Natural History of Neuroglia: an agenda for comparative studies. Neuron Glial Biology 1:97-100.
- Fields, R. D. (2006) Beyond the Neuron Doctrine. Scientific American Mind June/July 17:20-27.
Links:
- The Other Brain website
- R. Douglas Fields: Chief and Senior Researcher of the Section on Nervous System Development and Plasticity at the National Institute of Child Health and Human Development, which is part of NIH.
- Dr. Ichiji Tasaki; worked at NIH for over 50 years and was a pioneering researcher of nerve conduction. (See the episode transcript for links to the other researchers that were mentioned in this episode.)
Related Episodes of the Brain Science Podcast:
Announcements:
- The Brain Science Podcast application for iPhone/Touch now contains transcripts for all episodes. Your reviews are greatly appreciated.
- The next new episode of the Brain Science Podcast will come out in September, 2010.
- Be sure to check out my other podcast Books and Ideas.
- For more science podcasts go to http://sciencepodcasters.org.
- Stay informed by subscribing to the BSP Newsletter.
- Correction: Barbara Strauch is the author of The Secret Life of the Grown-up Brain: The Surprising Talents of the Middle-Aged Mind. (note the correct spelling of STRAUCH)
Listen to Episode 69
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