What Are Neuroglia Cells?

Neurons and Glial Cells
Cells of the Brain: neurons are yellow, astrocytes are orange, oligodendrocytes are grey and microglia are white. Credit: JUAN GARTNER/Science Photo Library/Getty Images

What Are Neuroglia?

Neuroglia, also called glial cells, are cells of the nervous system. They compose a voluminous support system that is essential to the proper operation of nervous tissue and the nervous system. Unlike neurons, glial cells do not have axons, dendrites, or conduct nerve impulses. Neuroglia are typically smaller than neurons and are about three times more numerous in the nervous system.

Glia perform a plethora of functions in the nervous system. These functions include providing support for the brain, assisting in nervous system repair and maintenance, assisting in the development of the nervous system, insulating neurons, and providing metabolic functions for neurons.

Types of Glial Cells and Their Function

There are several types of glial cells present in the central nervous system (CNS) and peripheral nervous system of humans. Six main types of neuroglia include:

  • Astrocytes
    Astrocytes are found in the brain and spinal cord and are 50 times more prevalent than neurons. Not only are astrocytes the most abundant neuroglia, but they are also the most abundant cell type in the brain. Astrocytes are noted for their star-shape. They reside in endothelial cells of the CNS that form the blood-brain barrier. This barrier prevents some substances from entering the brain and permits others entry. The two main categories of astrocytes are protoplasmic astrocytes and fibrous astrocytes. Protoplasmic astrocytes are found in the gray matter of the cerebral cortex, while fibrous astrocytes are found in white matter of the brain. The primary function of astrocytes is to provide structural and metabolic support for neurons. Additionally, astrocytes aid in signaling between neurons and brain blood vessels. This allows blood flow to increase or decrease depending on neuron activity. Other functions of astrocytes include glycogen storage, nutrient provision, ion concentration regulation, and neuron repair.
  • Ependymal Cells
    Ependymal cells are specialized cells that line the cerebral ventricles and central canal of the spinal cord. They are found within the choroid plexus of the meninges. These ciliated cells surround the capillaries of the choroid plexus and form cerebrospinal fluid (CSF). Functions of ependymal cells include CSF production, nutrient provision for neurons, filtration of harmful substances, and neurotransmitter distribution.
  • Microglia
    Microglia are extremely small cells of the central nervous system that remove cellular waste and protect against microorganisms (bacteria, viruses, parasites, etc.). Microglia are thought to be macrophages, a type of white blood cell that protects against foreign matter. They also help to reduce inflammation through the release of anti-inflammatory chemical signals. Microglia also function to protect the brain when neurons become injured or diseased by disabling the malfunctioning neurons.
  • Satellite Cells
    These glial cells cover and protect neurons of the peripheral nervous system. They provide structure and metabolic support for sensory, sympathetic, and parasympathetic nerves. Sensory satellite glial cells are involved in the development of chronic pain.
  • Oligodendrocytes
    Oligodendrocytes are central nervous system structures that wrap some neuronal axons to form an insulating coat known as the myelin sheath. The myelin sheath, composed of lipids and proteins, functions as an electrical insulator of axons and promotes a more efficient conduction of nerve impulses. Oligodendrocytes are found in the brain's white matter, while satellite oligodendrocytes are found in gray matter. Satellite oligodendrocytes do not form myelin.
  • Schwann Cells
    Schwann cells are neuroglia that wrap around some neuronal axons to form the myelin sheath in peripheral nervous system structures. Schwann cells help to improve nerve signal conduction, assist in nerve regeneration, and aid in antigen recognition by T cells. Schwann cells play a vital role in nerve repair. These cells migrate to the site of injury and release growth factors to promote nerve regeneration. Schwann cells then myelinate the newly generated nerve axons. Schwann cells are being heavily researched for their potential use in spinal cord injury repair.

Oligodendrocytes and Schwann cells indirectly assist in the conduction of impulses as myelinated nerves can conduct impulses quicker than unmyelinated ones. Interestingly enough, the white matter in the brain gets its color from the large number of myelinated nerve cells that it contains.

Other Animal Tissue Types

Neuroglia are just one type of tissue found in animal organisms. Other tissue types include:

Nervous Tissue: This is the primary tissue of the central nervous system. It is composed of neurons and is responsible for controlling body functions.

Epithelial Tissue: This tissue covers the outside of the body and lines organs. It provides a protective barrier against germs.

Connective Tissue: As the name suggests, connective tissue supports and connects tissues to other underlying tissues.

Muscle Tissue: The primary tissue responsible for movement, muscle tissue is capable of contraction.

Sources:

  • Purves, Dale. “Neuroglial Cells.” Neuroscience. 2nd Edition., U.S. National Library of Medicine, 1 Jan. 1970, www.ncbi.nlm.nih.gov/books/NBK10869/.
  • Sofroniew, Michael V., and Harry V. Vinters. “Astrocytes: Biology and Pathology.” SpringerLink, Springer-Verlag, 10 Dec. 2009, link.springer.com/article/10.1007/s00401-009-0619-8.
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Bailey, Regina. "What Are Neuroglia Cells?" ThoughtCo, Apr. 6, 2018, thoughtco.com/neuroglia-nervous-tissue-glial-cells-anatomy-373198. Bailey, Regina. (2018, April 6). What Are Neuroglia Cells? Retrieved from https://www.thoughtco.com/neuroglia-nervous-tissue-glial-cells-anatomy-373198 Bailey, Regina. "What Are Neuroglia Cells?" ThoughtCo. https://www.thoughtco.com/neuroglia-nervous-tissue-glial-cells-anatomy-373198 (accessed April 19, 2018).