What is the Difference Between Astrocytes and Microglia

The main difference between astrocytes and microglia is that neuroepithelial progenitors are the origin of astrocytes whereas hematopoietic common myeloid progenitor is the origin of microglia.

Astrocytes and microglia are two types of glial cells that occur in the central nervous system. The main function of both astrocytes and microglia is to support the central nervous system.

Key Areas Covered

1. What is Astrocytes
    – Definition, Structure, Function
2. What is Microglia
     – Definition, Structure, Function
3. Similarities Between Astrocytes and Microglia
    – Outline of Common Features
4. Difference Between Astrocytes and Microglia
    – Comparison of Key Differences

Key Terms

Astrocytes, Microglia

What are Astrocytes

Astrocytes are characteristic star-shaped glial cells in the brain and the spinal cord. They perform many functions in the central nervous system. In general, astrocytes have the biochemical control of endothelial cells of the blood-brain barrier. They also control the provision of nutrients to the nervous tissue. In addition, they maintain the extracellular balance while regulating cerebral blood flow. Moreover, astrocytes have a role in repair and scarring.

Figure 1: Astrocytes

The proportion of astrocytes in the brain differs from region to region. However, it is the most numerous type of cell in the brain. Usually, the proportion of astrocytes varies from 20% to 40% of all ganglia. The major source of cholesterol in the brain is astrocytes. Apolipoprotein E is responsible for the transport of cholesterol from astrocytes to neurons. In general, astrocytes control the concentration of ions. They also provide structural support to the synapses.

What are Microglia

Microglia are another type of glial cells that occur in the central nervous system. Generally, 7% of the cells in the brain are microglia. Microglia are the main form of active immune defense cells in the brain and the spinal cord. Microglia occurs in the large, non-overlapping regions of the central nervous system. Functionally, microglia are the key cells in brain maintenance. Therefore, they remove damaged or unnecessary neurons, synapses, plaques, and infectious agents. Microglia are also sensitive to small pathological changes in the CNS.

Figure 2: Microglia

Furthermore, direct access to pathogenic factors is not possible in the central nervous system. Generally, this is due to a series of endothelial cells called the blood-brain barrier. In the case of the direct introduction of pathogens to the brain across the blood-brain barrier, microglial cells quickly decrease inflammation by destroying infectious agents. In addition, microglia have to recognize foreign bodies, swallow them, and must serve as antigen-presenting cells in order to activate T cells. 

Similarities Between Astrocytes and Microglia

• Astrocytes and microglia are two types of glial cells that occur in the central nervous system.
• Their function is to support the central nervous system.

Difference Between Astrocytes and Microglia

Definition

Astrocytes refer to large, star-shaped cells that hold nerve cells in place and help them develop and work the way they should while microglia refer to cells of mesodermal/mesenchymal origin that migrate into the CNS to become resident macrophages within the unique brain microenvironment.

Origin

Neuroepithelial progenitors are the origin of astrocytes while hematopoietic common myeloid progenitor is the origin of microglia.

Structure

Astrocytes are tissue-embedded, nonmotile, and positionally stable while microglia contain processes with constant motion.

Function

Astrocytes nourish neurons while microglia protect neurons.

Conclusion

In brief, astrocytes and microglia are two types of glial cells that occur in the central nervous system. Astrocytes originate from neuroepithelial progenitors. They are typically tissue-embedded, nonmotile, and positionally stable. Moreover, the main function of astrocytes is to nourish neurons. Microglia, on the other hand, originate from the hematopoietic common myeloid progenitor and contain processes with constant motion. They also protect neurons. Therefore, the main difference between astrocytes and microglia is their structure and function.  

References:

1. Vainchtein ID, Molofsky AV. Astrocytes and Microglia: In Sickness and in Health. Trends Neurosci. 2020 Mar;43(3):144-154. doi: 10.1016/j.tins.2020.01.003. Epub 2020 Feb 7. PMID: 32044129; PMCID: PMC7472912.
2. Learning, Lumen. “Biology for Majors II.” Lumen, 

Image Courtesy:

1. “Human astrocyte” By Bruno Pascal – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Mikroglej 1” By GrzegorzWicher – Own Work (Public Domain) via Commons Wikimedia