Glia cells and neurons: structure and function

Gila Cells & Neurons

Glia cells, neurons, and the synaptic gap

Glia cells remain a little-understood quantity that exists in the nervous systems of virtually all living beings. Almost all creatures with a brain have these cells. Early experiments revealed that if the glia cells are removed in even a simple organism, the corresponding neurons die out, and if the neurons are removed, the corresponding glia cells die. Only one species of very simple worm has been found to live after the removal of its glia, and even then "over time, the neurons slowly deform into unrecognizable shapes, and abnormal functions" (Studying glia development, 2008, Virtual Worlds). Normal brain functioning and cognition are thus clearly interlinked to the correct interplay between glia cells and neurotransmitters. The degeneration of the developing brain of this species of worm suggests that glia "listen in" on neuronal communication and act based on what the glia "hear" from the chemical messenger cells of neurotransmitters in a vitally important way (Chen 2009).

Glia cells are located around the neurons, near long branches called axons that carry electrical signals to buds at the end of the branch of the neurons. The axon bud's neurotransmitters, the chemical messenger molecules, send the signal across a short synaptic gap to a "twig-like receptor, or dendrite, on an adjacent neuron" (Chen 2009). But the glia cells have a variety of receptors on their membranes that can also respond to chemicals like neurotransmitters. Glia can communicate by reacting to signals from neurotransmitters that neurons do not recognize (Chen 2009). This suggests that they have their own uniquely important role in the communication process.

Glia cells sense "neuronal action potentials by detecting ATP that is either released by a firing axon or leaked from the synapse. The glia cell relays the message inside itself via calcium ions. The ions activate enzymes that release ATP to other glial cells or activate enzymes that control the readout of genes" (Chen 2009). For example, glia cells are involved in the process of generating the myelin insulation around axons which is vital "to the conduction of nerve impulses at high speed over long distances. Its [mylelin insulation] growth enables a baby to gradually hold up its head, and its destruction by diseases such as multiple sclerosis causes severe impairment" (Chen 2009). Researchers have also found that both brain tumors and neurodegenerative diseases, such as Alzheimer's disease may be the result of problems with glia cells. Clearly, glia "are more than mere support cells that cater to the needs of neurons" and a "dynamic dialogue between glia and neurons takes place," contrary to what was once thought (Glia guide brain development in worms, 2008, Virtual Worlds).

In the case of the worm that had its glia removed, dendrites or communication receptors "were dramatically shortened and their axons, unable to branch to their expected locations, failed to make the right connections. Moreover, the team showed that neurons located closer to the removed glia have a more abnormal pattern of axon branching compared to those farther away, suggesting that a chemical glia secrete does, in fact, tell axons where to go and, perhaps, how to get there" (Glia guide brain development in worms, 2008, Virtual Worlds). Glia thus could be said to perform a kind of 'traffic cop' as well as communication function within the nervous system.