Neuroglia: Realising their true potential

Abstract

The name neuroglia is generally translated as nerve glue. In the recent past, this has been used to describe passive structural cells. Presently, this view has been challenged and the true dynamic and multifunctional nature of neuroglia is beginning to be appreciated. In the central nervous system, the main kinds of neuroglia are astrocytes (the primary homeostatic cells that ensure synaptic transmission), oligodendrocytes (which form the myelin that ensures rapid electrical transmission) and microglia (the main immune cells). In the peripheral nervous system, neuroglia comprise Schwann cells, satellite glia and enteric glia. These functionally diverse and specialised cells are fundamental to function at the molecular, cellular, tissue and system levels. Without nerve glue, the body cannot function and the future will begin to unlock their importance in higher cognitive functions that set humans apart from other animals and their true potential as therapeutic targets in neurodegenerative and other diseases.

Keywords: Glia; Schwann cell; astrocyte; enteric glia; microglia; oligodendrocyte; satellite glia.

Figure 1.

Neuroglial diversity. Neuroglia are sub-classified into CNS and PNS glia, but overall their functions are the same – to provide homeostatic, structural and metabolic support of neurons, to meylinate their axons to ensure rapid signal transmission and to be the main defensive and immunocompetent cells. In the CNS, the main glial cell types are astrocytes, oligodendrocytes and microglia. In the PNS, the main neuroglia are Schwann cells, satellite glial cells within the ganglia and enteric glia, which support neurons within the enteric nervous system of the gastrointestinal tract. The interface between the CNS and the PNS marks a change from an environment of astrocytes, oligodendrocytes and microglia, to one of Schwann cells and satellite glia; there is no change in the axon as it passes from one domain to the other, and PNS and CNS neurons are fundamentally the same. In the broadest sense, CNS and PNS neuroglia are essential for normal bodily function.

Figure 2.

Neuroglia in the CNS. CNS glia are multifunctional cells specialised to enable neurons to perform their function of information transfer. The division of labour between glia and neurons is fundamental to the evolution of the human brain into a supercomputer that fits within the small space of the cranium. It has taken over 100 years to redefine neuroglia as being more than brain glue. Nonetheless, the importance of glue should not be underestimated – the disruption of neuroglia has devastating effects on the neuronal function and is involved in every neuropathology. Quite literally, the brain falls apart without nerve glue and increased knowledge of glial cell biology is beginning to lead to a greater appreciation of the true potential of glial cells as therapeutic targets.