35.3: Neurons and Glial Cells - Glia
- Describe the specific roles that the seven types of glia play in the nervous systems
While glia (or glial cells ) are often thought of as the supporting cast of the nervous system, the number of glial cells in the brain actually outnumbers the number of neurons by a factor of ten. Neurons would be unable to function without the vital roles that are fulfilled by these glial cells. Glia guide developing neurons to their destinations, buffer ions and chemicals that would otherwise harm neurons, and provide myelin sheaths around axons. Scientists have recently discovered that they also play a role in responding to nerve activity and modulating communication between nerve cells. When glia do not function properly, the result can be disastrous; most brain tumors are caused by mutations in glia.
Types of Glia
There are several different types of glia with different functions. Astrocytes make contact with both capillaries and neurons in the CNS. They provide nutrients and other substances to neurons, regulate the concentrations of ions and chemicals in the extracellular fluid, and provide structural support for synapses. Astrocytes also form the blood-brain barrier: a structure that blocks entrance of toxic substances into the brain. They have been shown, through calcium-imaging experiments, to become active in response to nerve activity, transmit calcium waves between astrocytes, and modulate the activity of surrounding synapses. Satellite glia provide nutrients and structural support for neurons in the PNS. Microglia scavenge and degrade dead cells, protecting the brain from invading microorganisms. Oligodendrocytes form myelin sheaths around axons in the CNS. One axon can be myelinated by several oligodendrocytes; one oligodendrocyte can provide myelin for multiple neurons. This is distinctive from the PNS where a single Schwann cell provides myelin for only one axon as the entire Schwann cell surrounds the axon. Radial glia serve as bridges for developing neurons as they migrate to their end destinations. Ependymal cells line fluid-filled ventricles of the brain and the central canal of the spinal cord. They are involved in the production of cerebrospinal fluid, which serves as a cushion for the brain, moves the fluid between the spinal cord and the brain, and is a component for the choroid plexus.
Contributions and Attributions
- OpenStax College, Biology. October 17, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44745/latest...ol11448/latest . License : CC BY: Attribution
- OpenStax College, Biology. November 25, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44747/latest...ol11448/latest . License : CC BY: Attribution
- Nervous system. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Nervous_system . License : CC BY-SA: Attribution-ShareAlike
- neuron. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/neuron . License : CC BY-SA: Attribution-ShareAlike
- nervous system. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/nervous_system . License : CC BY-SA: Attribution-ShareAlike
- glial cell. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/glial_cell . License : CC BY-SA: Attribution-ShareAlike
- OpenStax College, Introduction. October 17, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44745/latest...e_35_00_01.jpg . License : CC BY: Attribution
- OpenStax College, Biology. November 25, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44747/latest...ol11448/latest . License : CC BY: Attribution
- OpenStax College, Biology. October 17, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44747/latest...ol11448/latest . License : CC BY: Attribution
- synapse. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/synapse . License : CC BY-SA: Attribution-ShareAlike
- dendrite. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/dendrite . License : CC BY-SA: Attribution-ShareAlike
- axon. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/axon . License : CC BY-SA: Attribution-ShareAlike
- OpenStax College, Introduction. October 17, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44745/latest...e_35_00_01.jpg . License : CC BY: Attribution
- OpenStax College, Biology. November 25, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44747/latest...ol11448/latest . License : CC BY: Attribution
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- OpenStax College, Biology. October 17, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44747/latest...ol11448/latest . License : CC BY: Attribution
- Boundless. Provided by : Boundless Learning. Located at : www.boundless.com//biology/de...on/radial-glia . License : CC BY-SA: Attribution-ShareAlike
- Boundless. Provided by : Boundless Learning. Located at : www.boundless.com//biology/de...satellite-glia . License : CC BY-SA: Attribution-ShareAlike
- astrocyte. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/astrocyte . License : CC BY-SA: Attribution-ShareAlike
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Key Points
- Glia guide developing neurons to their destinations, buffer harmful ions and chemicals, and build the myelin sheaths around axons.
- In the CNS astrocytes provide nutrients to neurons, give synapses structural support, and block toxic substances from entering the brain; satellite glia provide nutrients and structural support for neurons in the PNS.
- Microglia scavenge and degrade dead cells, protecting the brain from invading microorganisms.
- Oligodendrocytes form myelin sheaths around axons in the CNS; Schwann cell forms myelin sheaths around axons in the PNS.
- Radial glia serve as bridges for developing neurons as they migrate to their end destinations.
- Ependymal cells line fluid-filled ventricles of the brain and central canal of the spinal cord which produce cerebrospinal fluid.
Key Terms
- satellite glia : glial cell that provides nutrients for neurons in the PNS
- radial glia : glial cell that serves as a bridge for developing neurons as they move to their end destinations
- astrocyte : a neuroglial cell, in the shape of a star, in the brain