Glial cell

Definition

A non-neuronal cell of the nervous system that provides structural, metabolic, and homeostatic support to neurons without generating electrical impulses. In arthropods, glial cells include surface (perineurial) glia that form the outer blood-nerve barrier, cortex glia that ensheath neuronal cell bodies, and neuropil glia (including ensheathing and astrocyte-like subtypes) that invade synaptic regions and regulate ionic and neurotransmitter clearance. Arthropod glial cells are critical for maintaining the extracellular potassium balance necessary for sustained neural signaling, especially during high-frequency firing such as in flight motor patterns or escape responses.

Etymology

From Greek glia, 'glue', reflecting the original 19th-century view that these cells merely held neurons together; the term persists despite recognition of their active physiological roles.

Example

In the locust Schistocerca gregaria, giant glial cells in the ganglia exhibit spatial buffering of potassium ions released during intense neuronal activity, preventing depolarization block of the flight motor neurons that drive wing beating.

Synonyms

• neuroglia
• glia

Related Terms

• Neuron
• blood-brain barrier
• ganglion
• neuropil
• myelin
• astrocyte
• Schwann cell

Usage Notes

The term encompasses functionally analogous but evolutionarily distinct cell types across phyla. Arthropod glial cells lack true myelin (unlike vertebrate oligodendrocytes and Schwann cells) but form multilayered wrappings around axons in some crustaceans and insects that serve similar insulating functions. The relative abundance and morphological diversity of glial subtypes varies considerably between insect orders and life stages, with holometabolous insects showing dramatic reorganization of glial architecture during metamorphosis. In comparative neurobiology, 'glial cell' is preferred over 'neuroglia' when emphasizing cellular identity rather than tissue-level organization.