Neuroscience
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Microglia

Microglia, in contrast to the other types of glial cells, originate from embryonic mesoderm. They are present throughout the central nervous system, but tend to be inconspicuous in mature normal tissue and are difficult to identify with the light or electron microscope. They are more abundant in gray matter, and may compromise up to 5-10% of the neuroglia in the cerebral cortex.

The general appearance of microglia is similar to oligodendrocytes, although they are smaller and have undulating processes with spine-like projections. Microglial nuclei are elongated or triangular and stain deeply with alkaline dyes.

Following damage to nervous tissue, microglia proliferate and migrate to the site of injury where they clear cellular debris by phagocytosis. The reacting microglia have a swollen form with shortened processes and are difficult to discriminate from phagocytes from the periphery or migrating perivascular cells. It is estimated that at least one third of the phagocytes appearing in the area of a lesion are of CNS origin.

Figure 8.18

• View a Microglia cell

A. Neurons
B. Microglia
C. Fibrous astrocytes
D. Protoplasmic astrocytes
E. Macrophages