Glial Cells

Original Editor - Lucinda hampton

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Introduction[edit | edit source]

Neuroglia.png

The brain is made up of more than just neurones. Numerous glial cells give support to the neurones, and in addition aid in the maintenance of homeostasis, and form myelin. Although there are about 86-100 billion neurons in the brain, glial cells are the most abundant cells in the central nervous system.

Glial cells exist in the both central nervous system (CNS) and the peripheral nervous system (PNS).[1] The most notable glial cells include oligodendrocytes, astrocytes, microglia, and ependymal cells in the CNS and schwann cells, satellite cells, and enteric glial cells in the PNS,. Most glial cells are capable of mitotic division.[2][3][4] Size plays a role with the macroglia (larger glial cells) insulating, protecting, and helping neurons to develop and migrate. and the microglia (smaller types of glia) have phagocytic properties, digesting foreign particles.[5]

Glial Cell Types[edit | edit source]

Astrocytes[edit | edit source]

Astrocyte(green) in culture emitting many stellate extensions

Astrocytes are the most abundant cells in the brain. They are star-shaped cells that provide physical and nutritional support for neurons. Functions include: clean up brain "debris"; transport nutrients to neurons; hold neurons in place; digest parts of dead neurons; regulate content of extracellular space; promote synaptic connections; clear excess neurotransmitters; ensure the continued function of neurons[6].

Astrocytes also

  • Help to maintain the permeability of the blood-brain barrier where they sense glucose and ion levels inside the brain and regulate their flow into or out of it[5].
  • Are involved in gliosis in response to injury.[4]
  • Regulate extracellular fluid transport known as the glymphatic pathway (functionally represents the brain’s lymphatic system).[7]

Oligodendrocytes[edit | edit source]

Oligodendrocyte(green) & Astrocyte(red)

Oligodendrocytes are the myelin-forming cells of the CNS. . Myelin is composed of layered phospholipid membranes and serves to support and insulate axons, allowing for faster impulse transduction. Saltatory conduction occurs as the impulses jump across sodium ion-rich nodes of Ranvier. One oligodendrocyte myelinates multiple axons. Oligodendrocytes are incapable of replication upon injury[8].

Ependymal Cells[edit | edit source]

Sagittal view ventricular zone.

Ependymal cells, which create cerebral spinal fluid (CSF), line the ventricles of the brain and central canal of the spinal cord. These cells are cuboidal to columnar and have cilia and microvilli on their surfaces to circulate and absorb CSF

Depending on where they are located, ependymal cells also help to distribute neurotransmitters and hormones associated with the central nervous system. Also the microvilli of ependymal cells can absorb CSF and influence its flow and let certain substances in and out of the brain. Like the majority of glial cells, the ependyma also contributes to osmotic control within the brain via glucose and ion regulation[5].[8].

Radial Glia[edit | edit source]

Radial glial cells are at crucial in brain development, being the progenitors for neurons and macroglia (oligodendrocytes and astrocytes) and providing pathways for migration of neurons from the ventricular surface to their final positions in the brain.[9]

Interneuron(green)-radial(red)glial interactions, developing cerebral cortex

Radial glia also increased synapse stability, improve brain plasticity and play a role in neuroprotection. [10]

Microglia[edit | edit source]

Microglia phagoptosis of neuron cell.png

Microglia phagocytose and remove foreign or damaged material, cells, or organisms.[8] They are small, relatively sparse cells. They act as the brain's resident cleanup squad by phagocytosing apoptotic cells, plaques, and pathogens. In the resting healthy brain, microglia are highly dynamic, moving constantly to actively survey the brain parenchyma. [11] Microglia seem to be particularly involved in monitoring the integrity of synaptic function, optimizing different brain circuits to enable cognitive development (microglia cells eliminate previously-formed synapses that are no longer useful).[12]

Triggering of an immune response is a regular feature in neurodegenerative disorders, making microglia cells be in chronically activated phenotype. This is seen to be a contributing factor to neuronal dysfunction and cell death and is a current area of research.[13]

Schwann Cells[edit | edit source]

Satellite and Schwann cells, PNS

Schwann Cells (glial cell of the PNS) surrounds neurons, keeping them alive and covering them with a myelin sheath. They play essential roles in the development, maintenance, function, and regeneration of peripheral nerves.

Satellite Glial Cells[edit | edit source]

Satellite Glial Cells ensheath the somata of neuron bodies in sensory, sympathetic and parasympathetic ganglia. They are thought to have a similar role to astrocytes in the central nervous system (CNS). They supply nutrients to the surrounding neurons and also have some structural function. Satellite glial cells bundle the axons close together by surrounding them, keeping them from touching each other by squeezing its cytoplasm between the axons.[14]

References[edit | edit source]

  1. Radiopedia Glial cells Available from: https://radiopaedia.org/articles/glial-cells(last accessed 18.12.2020)
  2. Yuhas D, Jabr F. Know Your Neurons: What Is the Ratio of Glia to Neurons in the Brain?.Available from; https://blogs.scientificamerican.com/brainwaves/know-your-neurons-what-is-the-ratio-of-glia-to-neurons-in-the-brain/(last accessed 18.12.2020)
  3. Queensland Brain Institute Types of Glia Available:https://qbi.uq.edu.au/brain-basics/brain/brain-physiology/types-glia (accessed 21.1.2023)
  4. 4.0 4.1 Ludwig PE, Das JM. Histology, glial cells. InStatPearls [Internet] 2021 May 10. StatPearls Publishing.Available:https://www.ncbi.nlm.nih.gov/books/NBK441945/ (accessed 21.1.2023)
  5. 5.0 5.1 5.2 Biology Dic Glial cells Available:https://biologydictionary.net/glial-cells/ (accessed 10.5.2022)
  6. Washington Faculty neuroscience for kids Available from:https://faculty.washington.edu/chudler/glia.html (accessed 18.12.2020)
  7. radiopedia glymphatic pathway Available from:https://radiopaedia.org/articles/glymphatic-pathway?lang=gb (accessed 18.12.2020)
  8. 8.0 8.1 8.2 Ludwig PE, Das JM. Histology, Glial Cells. StatPearls [Internet]. 2020 Jun 19.Available from:https://www.ncbi.nlm.nih.gov/books/NBK441945/ (accessed 18.12.2020)
  9. Arellano JI, Morozov YM, Micali N, Rakic P. Radial glial cells: new views on old questions. Neurochemical research. 2021 Oct;46(10):2512-24. Available:https://pubmed.ncbi.nlm.nih.gov/33725233/ (accessed 25.1.2023)
  10. Psychology Wiki. Radial Glia Available from: https://psychology.wikia.org/wiki/Radial_glial_cells (accessed 19.12.20200
  11. Scanlon ST. Depressing effects of microglia. Science. 2020 Apr 17;368(6488):279-80.Available from;https://science.sciencemag.org/content/368/6488/279.2.full (last accessed 18.12.2020)
  12. Wake H, Moorhouse AJ, Nabekura J. Functions of microglia in the central nervous system-beyond the immune response. Neuron glia biology. 2011 Feb 1;7(1):47.Available from:https://www.cambridge.org/core/journals/neuron-glia-biology/article/abs/functions-of-microglia-in-the-central-nervous-system-beyond-the-immune-response/B262044DDADE74974C8A268DD258B29A (accessed 18.12.2020)
  13. Tejera D, Heneka MT. Microglia in neurodegenerative disorders. Microglia. 2019:57-67. Available:https://pubmed.ncbi.nlm.nih.gov/31392677/ (accessed 25.1.2023)
  14. Lavdas AA, Matsas R. Schwann cell morphology. Available: https://www.sciencedirect.com/science/article/pii/B9780128012383047589 (accessed 10.5.2022)