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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.