PN 003 Microglia

Microglia

Transmission electron microscopy (TEM) of the cerebral cortex. This large composite image shows a microglia and the surrounding neuropil.

• Microglia (purple)
• Pyramidal Neurons (green)
  • Dendrites (dark green)
  • Dendritic Spines (light blue)
• Axon Terminals (orange) - form synapses with dendritic spines
  • Synaptic vesicles (purple)
• Protoplasmic Astrocytes (tan)
• Capillary (light red) - surrounded by a basal lamina (purple)

We will take a closer look at microglia in the following pages.

Subcellular Structures

• Nucleus (blue) / Nuclear Envelope (purple)
• Golgi Apparatus (yellow)
• Mitochondria (red)
• Endoplasmic Reticulum (cyan)

Courtesy of Patrick C. Nahimey, Division of Medical Sciences, University of Victoria, Victoria, British Columbia, Canada.

Microglia

Microglia are resident immune cells in the central nervous system. They engulf and digest dead cells, cellular debris, and pathogens, similar to macrophages in the rest of the body. They are the smallest and least numerous of the glial cells.

• Cell Body - small nucleus (blue) of condensed chromatin and little cytoplasm
  • Distinctive long cisternae of rough endoplasmic reticulum (cyan), contrary to other glial cell types
  • Active microglia have many lysosomes, lipofuscin, and other lipid bodies
• Processes - extend long, thin processes with irregular contours
  • Highly dynamic, rapidly extending and retracting to survey their environment
• Cytoskeleton - significantly fewer filaments compared to other glial cell types
  • Dynamic rearrangement of actin filaments is crucial for motility and phagocytosis

When microglia detect a problem, they undergo a process known as “activation.” The cell body enlarges as processes retract to allow movement toward areas of injury, inflammation, or infection. The activated microglia become phagocytic clearing away cellular debris or foreign substances.