Our nervous system has very few neurons as compared to the neuroglial cells. The ratio of neurons versus neuroglial cell is approximately 1:10. Neuroglial cells are found both in vertebrates and invertebrates. They unlike neurons lack axons, form no synapses and have the capability of dividing throughout the life span. Though neuroglia and neurons lie close by but there is no direct intersection specialization like gap junctions between them. Originally neuroglia was believed to support the structure for neurons. However, research proved that there are other functions that neuroglia performs like oligodendrocytes or Schwann cells producing a myelin sheath circling the neuronal axons. Below are mentioned the various kinds of neuroglia found and their functions.
Astrocyte means star-shaped cell. They are divided into two types – Fibrous astrocytes that are predominant amongst myelinated nerve fibers, are found in the white matter present in the central nervous system with many fibrils in the cytoplasm and Protoplasmic astrocytes that are present in the grey matter with lesser number of fibrils in the cytoplasm. Organelles observed in somata of a neuron are present in astrocytes, but in lesser numbers. The important processes leave the cell in a circular direction forming end feet and expansions at the exteriors of the vascular capillaries.
Oligodendrocytes are well-developed with fewer cytoplasmic fibrils. These can be differentiated from astrocytes because their nucleus and cytoplasms have better density, due to the deficiency of glycogen in the fibrils and cytoplasm, and enormous quantities of microtubules. Inter-fascicular oligodendrocytes are lined up in rows amidst nerve fibers of the white matter of the CNS. Perineuronal oligodendrocytes are found, on the other hand, close to the somata of nerve cells in the grey matter.
Microglial are small-sized, crenate cells having a darkish nucleus and cytoplasm. No one knows if microglial cells are simply damaged neuroglia or arise as a distinct group in live tissue.
One of the well-known roles of neuroglia is to repair injury caused to the central nervous system. Astrocytes divide and fill in gaps created by damaged neurons, whereas oligodendrotes proliferate to form the myelin sheath.
The nerve cells of the peripheral nervous system when cut regenerate after degeneration in a manner that they come back to their natural target positions. The route is marked by Schwann cells and astrocytes. For cerebellum and cerebral cortex development, astrocytes project lengthy processes and neurons travel across these processes and reach their destinations.
Astrocytes have high-affinity acceptance systems like glutamate and gamma-aminobutyric acid for neurotransmitters. This is an important function as it helps in the modulating synaptic transmission. Research has shown that neuroglia is electrically excitable as one of their properties is that they are voltage-sensitive. Neuroglial cells also give-and-take substances like ions, amino acids, and glucose with more cellular fluid to exert control upon the neuronal surroundings.
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