Numbers
Neuroglial cells are generally smaller than neurons and outnumber them by five to ten times; they comprise about half the total volume of the brain and spinal cord.(Clinical Neuro-Anatomy, Richard S. Snell, 7th edition) The ratio differs from one part of the brain to another. The glia/neuron ratio in the cerebral cortex is 3.72 (60.84 billion glia; 16.34 billion neurons) while that of the cerebellum is only 0.23 (16.04 billion glia; 69.03 billion neurons). The ratio in the cerebral cortex gray matter is 1.48 (the white matter part has few neurons). The ratio of the basal ganglia, diencephalon and brainstem combined is 11.35.
Most cerebral cortex glia are oligodendrocytes (75.6%); astrocytes account for 17.3% and microglia (6.5%)
The amount of brain tissue that is made up of glial cells increases with brain size: the nematode brain contains only a few glia; a fruitfly's brain is 25% glia; that of a mouse, 65%; a human, 90%; and an elephant, 97%.
Read more about this topic: Neuroglia
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