V. Microglia

A. Characteristics of normal microglia

Microglia are mesoderm-derived cells (in contrast to the macroglia -- astrocytes, oligodendrocytes, and ependyma -- which are derived from neuroectoderm).  Microglia are the CNS representatives of the reticuloendothelial system.  One major function is to serve as a fixed macrophage system. 

B. Pathological reactions

Microglial cells become activated in response to injury and may respond by

• proliferation
• developing elongated nuclei (rod cells)
• forming aggregates around areas of tissue necrosis or dying neurons (neuronophagia, microglial nodule or shrub

In addition to microglia, blood-derived macrophages serve as phagocytic cells in the CNS.