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In our continuing discussions on action potentials, synapses, neurons, and the senses I wonder why glial cells seemed to have been overlooked. I realize that there isn't much literature out there concerning these cells especially since neurons have been getting most of the attention. Whenever someone mentions "brain cells", he or she is most likely refering to neurons, the cells responsible for the hard wiring of the brain by sending and receiving both chemical (neurotransmitters) and electrical information. But I read in my research for the first web paper that neurons only account for approximately 10 percent of the brain. The other 90 percent is made up of glial cells. Is this alarming (ok, surprising to me) proportion indicative of some underlying concept of the glia-neuron relationship?

In my research about neuroplasticity, it was revealed that some glial cells perform some of the same functions that neurons were thought to be solely responsible for: emitting and receiving neurotransmitters. To further research on glial cells I stumbled upon an article (link provided below) describing a study by Rockefeller University on C. elegans that suggests the glial cell's importance to sensory reception. The study concerned the amphid, an organ in the C. elegan's nervous system that contains both glia and neurons. The organ contains 12 neurons 4 of which are completely surrounded by glial cells while 8 are partially surrounded with sensory endings exposed. To test the importance of glia to the neurons, the scientists removed the glia and observed the resulting shape of the neurons, the neuron's ability to respond to odors and temperatures, and the neuron's ability to absorb certain dyes. In the absence of glia, the neurons that were once completely surrounded shrivelled but the neurons that were once partially surrounded maintained their shape. However, these 8 neurons responsible for receiving stimuli from the environment were rendered useless. The C. elegans displayed trouble in finding their ideal temperature by crawling towards higher and higher teperatures. Their sense of smell was also affected by showing no preference or aversion to particular odors. From a molecular standpoint, the researchers focused on FIG-1, a protein secreted by only glia surrounding the amphid sensory organ. Without this protein, the neurons of the sensory organ had trouble processing external stimuli. Since FIG-1 in C. elegans resembles thrombospondin, the protein secreted by glia in vertabrates, the researchers suggest that the glia-neuron relationships observed in C. elegans may elucidate glia-neuron relationships in humans.

Without Glial Cells, Animals Lose Their Senses