Did you know that most of the central nervous system (CNS) cells are not neurons?
Glial cells, also called neuroglia or simply glia, greatly outnumber neurons in the CNS, the brain and the spinal cord. The word glia comes form the Greek word for “glue”, as glial cells were initially thought of being just a glue of the nervous system that hold neurons in place. However researchers have found this description to be greatly insufficient as novel functions of glia have shown them to be extremely important for neuronal homeostasis, function and metabolism in both healthy and pathogenic state.
Under microscope both neurons and glia look very similar to the untrained eye. Even for someone experienced, subtle differences in morphology of neurons and glia might not be that obvious. The main difference between neurons and glia is that the neurons are able get electrochemically stimulated due to changes in their intracellular ion concentrations and fire action potentials that are the , whereas glia are not able to do so.
Some of the very common glia in CNS are as follows:
Astrocytes: Most abundant cell type in CNS! They are named after their star-like shape. Astrocytes form the blood brain barrier and function in regulation of interaction between two neurons at sites called synapses.
Oligodendrocytes: Lipid-rich insulators of neuronal projections that speed up the propagation of action potentials to reach nerve terminals and proceed on to next neuron by traveling across synapses.
Microglia: Scavenger cells that remove cellular debris at sites of injury.
Interestingly even though neurons are not able to regenerate in adult CNS, glia can undergo cell division. In fact after a serious injury or stroke, glia often undergo an extensive degree of proliferation, forming reactive glia at the site of damage. Since developmentally glia and neurons are generated from a common progenitor, some researchers are trying to convert glial cells that proliferate at the scar site into functional neurons. This will especially be important for patients of CNS injuries, e.g. traumatic brain injury (TBI) or spinal cord injuries, where there is currently no treatment for recovering human nerve function after injury to the central nervous system.
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