Your brain doesn't just contain neurons: Neurons versus Glial Cells
Updated: Dec 19, 2018
There is a stark difference between neurons and glial cells, both of which are key towards the functioning of the human brain. However, their difference can be summed up by the following image :
Firstly, types of each cell. The neuron can be divided into sensory, motor and interneurons (as well as unipolar, multipolar etc). By contrast, glial cells is an umbrella term for a variety of support cells: Astrocytes, Microglia, Oligodendroglia, Satellite cells, and Schwann cells, all of which are key to the neural support system (outlined below). The number and divisions of the various kinds of neurons and glial cells differ, making them unrelated.
This links onto the function of each type of cell. The neuron, being incredibly specialized, at a cellular level has primarily one overarching function: to fire. By this, I mean that the neuron has the potential to transmit electrical impulses across a synapse to the next, ultimately resulting in higher order functions such as movement and thought. Their functions can therefore broadly be divided into two areas: receiving and transmitting information. Conversely, each type of glial cell has its own specific functions that differ from neurons, such as the formation of myelin (the protective fatty sheath facilitating rapid electrical signalling) , guiding migration of neurons during neural development , regulating neurotransmitter release, axonal guidance and formation, and even inflammatory and immune responses. Evidently, the roles of neurons and glial cells differ greatly.
Moreover, if both types of cells differ in function, it is inevitable that they will differ in structure. Below are images of neurons and glial cells:
Glial cells :
The clear differences among the two are the inevitable lack of the long protruding axon in most glial cells (except for perhaps the oligodendryte). Furthermore, neurons have two protrusions on each end, referred to as dendrites and axons, while glial cells only have a singly labelled outgrowth. Moreoever, glial cells are unable to transmit signals or messages across each other via action potentials, and hence only have a resting potential - whereas neurons have the capacity to generate action potentials as well. Glial cells also lack the capability to release neurotransmitters as opposed to neurons; However, this is being contested with recent research displaying possible neurotransmission by astrocytes. Hence up until now, glial cells have known to be more as the bystanding support system of cells, but it is still an ongoing topic of research. I have also read sites stating that the glial cells ‘clean up’ and ‘provide nutrients’ to neurons, but have not been able to find much research indicating how this occurs, except by perhaps activing pro-inflammatory cytokines that support cell apoptosis during neuronal damage.
Lastly, there is a difference in their discovery - the first evidence for glial cells in 1824 dates much before the discovery of the first neuron in 1891.