Key Roles of Neuroglia in the Nervous System Explained
Neuroglia Meaning
Neuroglia Definition: Glia, also known as glial cells or neuroglia, are non-neuronal cells that do not contain electrical impulses in the central nervous system (brain and spinal cord) and peripheral nervous system. Neuroglia definition tells that it helps neurons maintain homeostasis by forming myelin and providing support and defence.
Oligodendrocytes, astrocytes, ependymal cells, and microglia are glial cells in the central nervous system, while Schwann cells and satellite cells are glial cells in the peripheral nervous system. They serve four primary purposes: to protect and keep neurons in location, to deliver nutrients and oxygen to neurons, to insulate one neuron from some other, and to eliminate pathogens and damaged neurons.
They're also involved in neurotransmission and synaptic interactions, as well as physiological functions including breathing. Although it was once believed that glia outnumbers neurons by a factor of ten, recent research using newer technologies and reappraisal of historical quantitative data indicates a ratio of less than one to one, with significant variation between brain tissue.
Glial cells are much more diverse and functional than neurons, and they can respond to and control neurotransmission in a variety of ways. They may also have an effect on memory consolidation and retention.
Types:
Macroglia:
It is derived from ectodermal tissue.
Microglia:
Microglia are phagocytosis-capable specialised macrophages that defend central nervous system neurons. They're made up of the first wave of mononuclear cells, which emerge from yolk sac blood islands early in development and colonise the brain soon after neural precursors start to differentiate. These cells can be located in any part of the brain and spine. Microglial cells are smaller than macroglial cells, with oblong nuclei and a shifting form. They move around inside the brain and expand once it is affected. Microglia systems in a stable central nervous system actively sample all facets of their environment (macroglia, neurons, and blood vessels).
Other Forms:
Pituicytes are glial cells containing astrocyte-like features that come from the posterior pituitary. Tanycytes are ependymal cells that descend from radial glia and form the bottom of the third ventricle in the hypothalamus' median eminence. The fruit fly, Drosophila melanogaster, has a variety of glial forms that are functionally identical to mammalian glia but are categorised differently.
Total Number:
Neuroglial cells are generally smaller than neurons. In the human brain, there have been about 85 billion glial cells, which is about the same amount as neurons. Glial cells account for almost half of the brain and spinal cord's total number. The proportion of glia to neurons varies from one region of the brain to the next. In the cerebral cortex, the glia to neuron ratio is 3.72 (60.84 billion glia 72 per cent); whereas in the cerebellum, it is just 0.23. (16.04 billion glia; 69.03 billion neurons). The grey matter ratio throughout the cerebral cortex is 1.48, while the grey and white matter combined is 3.76. The basal ganglia, diencephalon, and brainstem have a cumulative ratio of 11.35.
Development
The majority of glia come from the developing embryo's ectodermal tissue, especially the neural tube and crest. Microglia, which are formed from hematopoietic stem cells, are an exception. Microglia are indeed a self-renewing group in adults, as opposed to macrophages and monocytes, that invade a diseased or injured CNS.
Glia emerges from the ventricular region of the neural tube in the central nervous system. Oligodendrocytes, ependymal cells, and astrocytes are examples of glia. The neural crest gives rise to glia in the peripheral nervous system. and satellite glial cells in ganglia Schwann cells in nerves are examples of PNS glia.
Capacity to Divide:
In maturity, glia maintains the capacity to divide cells, while most neurons do not. The theory is grounded on the mature nervous system's failure to substitute neurons after an accident, including a stroke or trauma, where there seems to be frequently a significant proliferation of glia, or gliosis, close or at the site of injury.
Recent findings, on the other hand, have shown zero evidence that 'mature' glia, including astrocytes or oligodendrocytes, maintain mitotic potential. If the nervous system matures, just the resident oligodendrocyte precursor cells appear to retain this capacity.
Mitosis is believed to occur in glial cells. On the other hand, scientists were also debating whether neurons are fully post-mitotic or worthy of mitosis. Glia was once thought to lack those characteristics of neurons.
What are Neuroglial Cells Functions?
Neuroglial Cells Function:- Few glial cells are mainly responsible for providing physical support to neurons. Others, particularly those involving neurons and their synapses, supply resources to neurons and control the extracellular fluid of the brain. Glial cells guide the migration of neurons throughout early embryogenesis and generate molecules that stimulate the production of axons and dendrites.
Neuron Repair and Development:
Glia plays an important role in the nervous system's growth as well as synaptic plasticity as well as synaptogenesis. Glia is involved in the control of neuronal repair after damage. Glia in the central nervous system inhibits repair. Astrocytes, which are glial cells, expand and proliferate to create a scar and develop inhibitory molecules which prevent an axon from regrowing after it has been weakened or severed.
Schwann cells (also termed as neuri-lemmocytes) are glial cells that facilitate recovery in the peripheral nervous system (PNS). Schwann cells regress to a prior developmental state following axonal injury to promote axon regrowth. This distinction between the CNS and the PNS raises expectations for CNS nerve tissue regeneration.
Myelin Sheath Creation:
Oligodendrocytes are octopus-like cells that have bulbous cell bodies and up to fifteen arm-like processes. They are located in the CNS. Each mechanism extends out to an axon and forms a myelin sheath around it. The myelin sheath protects nerve fibres from extracellular fluid while also speeding up the signal transmission.
Schwann cells are required for myelin formation in the peripheral nervous system. Such cells wind constantly across nerve fibres in the PNS to surround them. This procedure results in the formation of a myelin sheath, that helps not just in conductivity as well as in the regeneration of damaged fibres.
Neurotransmission:
Astrocytes play an important role in the tripartite synapse. Neuroglial cells perform a variety of important roles, including clearing neurotransmitters from the synaptic cleft, that helps in differentiating between different action potentials and avoids the toxic build-up of these kinds of neurotransmitters, including glutamate, that might otherwise result in excitotoxicity. In addition, when astrocytes are stimulated, they produce gliotransmitters including glutamate, ATP, and D-serine.
What is Neuroglial Cells Clinical Significance?
Although glial cells in the PNS often help to restore lost neural function, neuroglia in the CNS may not respond in the same way. Regrowth of the CNS occurs only if the damage was mild rather than extreme. When a serious injury occurs, the survival of the surviving neurons has become the only option.
Nevertheless, some research into the function of glial cells in Alzheimer's disease is starting to cast doubt on this feature's utility, even claiming that it can "exacerbate" the disease. Scarring and inflammation from glial cells have also been linked to the degeneration of neurons in amyotrophic lateral sclerosis, in addition to affecting the eventual regeneration of neurons in Alzheimer's disease.
A diverse variety of adverse exposures, including hypoxia or physical trauma, may contribute to physical harm to the CNS, in contrast to neurodegenerative diseases. Once the CNS is damaged, glial cells usually induce apoptosis in the neighbouring cellular bodies. Then there will be a lot of microglial activity, that causes inflammation, and then there is a lot of growth inhibitory molecules released.
FAQs on Neuroglia: Types, Functions, and Significance
1. What are neuroglia and what is their primary role in the nervous system?
Neuroglia, also known as glial cells, are non-neuronal cells that form a major component of the nervous system. Unlike neurons, they do not generate or conduct nerve impulses. Their primary role is to provide support, protection, and nourishment to neurons. They maintain homeostasis, form the insulating myelin sheath around axons, and play an active role in synaptic function and overall neural health.
2. What are the six main types of neuroglial cells and their functions?
The six main types of neuroglia are categorised by their location in either the Central Nervous System (CNS) or the Peripheral Nervous System (PNS):
- Astrocytes (CNS): Provide structural support, help form the blood-brain barrier, and regulate the chemical environment around neurons.
- Oligodendrocytes (CNS): Produce the myelin sheath that insulates axons within the CNS, enabling faster signal transmission.
- Microglia (CNS): Act as the brain's resident immune cells, removing cellular debris and pathogens through phagocytosis.
- Ependymal Cells (CNS): Line the brain's ventricles and the spinal cord's central canal, producing cerebrospinal fluid (CSF).
- Schwann Cells (PNS): Form the myelin sheath around axons in the PNS and are crucial for the regeneration of damaged nerves.
- Satellite Cells (PNS): Surround neuron cell bodies in peripheral ganglia, regulating their chemical environment and providing support.
3. Can neuroglial cells regenerate, and how does this differ from neurons?
Yes, most types of neuroglial cells are capable of mitosis and can regenerate throughout life. This ability is crucial for responding to injury, where they proliferate in a process called gliosis to form a glial scar. This is a fundamental difference from most neurons in the central nervous system, which are largely post-mitotic, meaning they lose their ability to divide and have very limited capacity for regeneration after being damaged.
4. Why are neuroglia often called the "supporting cells" of the nervous system?
Neuroglia are called "supporting cells" because they perform all the essential maintenance and caretaking functions that allow neurons to work properly. While they don't transmit the primary nerve signals, they provide structural scaffolding for neural tissue, supply neurons with nutrients, insulate their axons with myelin, defend against pathogens, and precisely control the extracellular environment. They essentially create and maintain the optimal conditions required for neuronal function.
5. How do the functions of neuroglia in the CNS differ from those in the PNS?
The key functional difference lies in myelination and specialised roles. In the Central Nervous System (CNS), a single Oligodendrocyte can myelinate segments of multiple axons. In contrast, in the Peripheral Nervous System (PNS), a single Schwann cell myelinates only one segment of one axon. Furthermore, cells like Astrocytes (forming the blood-brain barrier) and Microglia (primary immune defense) are exclusive to the CNS, while Satellite cells provide support to ganglia only in the PNS.
6. If neuroglia don't transmit nerve impulses, what is a key function they perform that neurons cannot?
A crucial function that neuroglia perform, and neurons cannot, is myelination. Specialized glial cells—Oligodendrocytes in the CNS and Schwann cells in the PNS—wrap themselves around neuronal axons to form an insulating myelin sheath. This insulation is essential for saltatory conduction, a process that dramatically increases the speed and efficiency of nerve impulse transmission. Neurons generate the signals, but they depend entirely on neuroglia for this high-speed conduction.
7. What is the clinical significance of myelination by neuroglia?
Myelination by neuroglia is clinically vital for proper nervous system function. Damage to this myelin sheath, known as demyelination, is the cause of severe neurological disorders. For example, in Multiple Sclerosis (MS), the immune system attacks and destroys the myelin produced by oligodendrocytes in the CNS, leading to impaired coordination, muscle weakness, and sensory problems. Similarly, damage to Schwann cells in the PNS is characteristic of conditions like Guillain-Barré syndrome.
8. What is the role of microglia in brain health and disease?
Microglia act as the dedicated immune sentinels of the central nervous system. In a healthy state, they constantly survey their environment. Upon detecting injury, infection, or abnormal proteins, they become activated to perform phagocytosis, which is the process of engulfing and clearing away pathogens and cellular debris. While this protective role is vital for brain health, chronic or dysfunctional activation of microglia is also implicated in the progression of neurodegenerative diseases such as Alzheimer's and Parkinson's disease.
