Glia, also known as glial cells or neuroglia, play an active role in maintaining homeostasis in the central nervous system (CNS), which includes the brain and spinal cord, as well as the peripheral nervous system. Glia, non-neuronal cells, do not generate electrical impulses themselves. The neuroglia definition underscores their contribution to supporting and defending neurons by forming myelin.

In the CNS, glial cells such as oligodendrocytes, astrocytes, ependymal cells, and microglia perform essential functions. In the peripheral nervous system, Schwann cells and satellite cells are the glial components. These cells serve four primary purposes: protecting and stabilizing neurons, delivering nutrients and oxygen to neurons, insulating one neuron from another, and removing pathogens and damaged neurons. Glia actively participate in neurotransmission, synaptic interactions, and physiological functions like breathing. Contrary to the previous belief that glia outnumber neurons by a factor of ten, recent research utilizing advanced technologies and a reevaluation of historical quantitative data suggests a ratio of less than one to one, with considerable variation in different brain tissues.

Notably, glial cells exhibit greater diversity and functionality than neurons. They can respond to and modulate neurotransmission through various mechanisms and may also impact memory consolidation and retention.

There are several types of neuroglial cells, each with specific roles and functions:

1. Astrocytes

   – Most abundant glial cells in the central nervous system (CNS).

   – Provide physical support to neurons and help maintain the blood-brain barrier.

   – Regulate the chemical environment by taking up excess neurotransmitters and ions.

   – Contribute to the formation of neural synapses.

2. Microglia

Microglia actively defend central nervous system neurons as phagocytosis-capable specialized macrophages. The first wave of mononuclear cells, emerging from yolk sac blood islands early in development, forms microglia, which colonize the brain soon after neural precursors start differentiation. These cells can be found throughout the brain and spine. Microglial cells, smaller than macroglial cells, have oblong nuclei and a dynamic form. They move within the brain and proliferate in response to damage. In a stable central nervous system, microglia actively sample all aspects of their environment, including macroglia, neurons, and blood vessels.

3. Oligodendrocytes

   – Found in the CNS.

   – Responsible for producing and maintaining myelin, a fatty substance that insulates axons and enhances the speed of nerve impulse transmission.

4. Schwann Cells

   – Found in the peripheral nervous system (PNS).

   – Similar to oligodendrocytes, Schwann cells produce myelin to insulate peripheral nerves.

   – Aid in the regeneration of damaged peripheral nerves.

5. Ependymal Cells

   – Line the brain’s ventricles and the spinal cord’s central canal.

   – Involved in the production and circulation of cerebrospinal fluid (CSF).

6. Radial Glia

   – Play a crucial role in the development of the nervous system.

   – Serve as a scaffold for migrating neurons during embryonic development.

   – Differentiate into neurons or glial cells.

Collectively, neuroglial cells provide structural support, insulation, immune defense, and homeostasis within the nervous system. While neurons are primarily responsible for transmitting electrical signals, neuroglia plays indispensable roles in maintaining the overall health and functionality of the nervous tissue. The intricate interactions between neurons and neuroglia contribute to the complex and dynamic nature of the nervous system.

Neuroglial Cell Functions:

Physical Support and Resource Supply:

• Glial cells provide physical support to neurons.
• Some glial cells supply resources to neurons and regulate extracellular fluid in the brain.
• They guide the migration of neurons during embryogenesis and produce molecules that stimulate axon and dendrite production.

Neuron Repair and Development:

• Glia contributes to nervous system growth, synaptic plasticity, and synaptogenesis.
• In the central nervous system (CNS), astrocytes inhibit repair by creating inhibitory molecules and scar tissue.
• Schwann cells in the peripheral nervous system (PNS) facilitate recovery by promoting axon regrowth.

Myelin Sheath Creation

• Oligodendrocytes in the CNS form myelin sheaths around axons, protecting nerve fibers and speeding up signal transmission.
• Schwann cells in the PNS wind around nerve fibers, creating myelin sheaths that aid in conductivity and fiber regeneration.

Neurotransmission

• Astrocytes play a vital role in the tripartite synapse, clearing neurotransmitters from the synaptic cleft and preventing toxic build-up.
• Stimulated astrocytes release gliotransmitters like glutamate, ATP, and D-serine.

Neuroglial Cell Clinical Significance

• In CNS Repair:
• Glial cells in the PNS aid in restoring lost neural function, but CNS response to injury is limited.
• Regrowth in the CNS occurs only with mild damage; severe injuries may lead to survival of existing neurons.
• Neurodegenerative Diseases:
• Research suggests glial cells in Alzheimer’s disease may exacerbate the condition.
• Glial cells’ scarring and inflammation are linked to neuron degeneration in amyotrophic lateral sclerosis and affect neuron regeneration in Alzheimer’s disease.
• Physical Harm to CNS:
• Adverse exposures like hypoxia or trauma can cause physical harm to the CNS.
• Glial cells induce apoptosis in damaged CNS areas, leading to inflammation and the release of growth-inhibitory molecules.

Understanding neuroglial cell functions is crucial for comprehending their roles in neural health, repair, and diseases.