Also called glia, the neuroglia is a group of interstitial support cells whose bodies and outgrowths fill the spaces in the brain and spinal cord between the capillary blood vessels and the nerve cells (neurons). Thus, each neuron is surrounded by these supportive cells that provide it with nutrients and the myelin sheath which covers the nerve cell axon. The neuroglia is composed of astrocytes, oligodendrocytes, and microglia, which are migratory phagocitic cells. The microglia occupies a special position among neuroglial cells as they are “scavenger” of the CNS.
The neuroglia is evenly distributed over the entire brain and accounts for approximately 40 percent of the brain’s volume. There are about 190 billion neuroglial cells within a human being's central nervous system (CNS). They differ from neurons in size, as they are three to four times smaller than a nerve cell). They also differ from the nerve cells in morphological and biochemical characteristics. In contrast to neurons, the cells of the neuroglia retain the capacity to divide, while the neurons divide only under especial conditions, with an individual healthy lifestyle.
Function
The neuroglia acts as a protective layer for the neurons and forms part of the blood-brain barrier between the capillaries carrying oxygenated blood and the encephalic neurons. This barrier regulates the passage of matter between the capillary blood and the CNS. Neuroglia astrocytes supply the neurons with nutrients, glucose, and ketone bodies (when the diet is based on fat instead of carbs), while the oligodendrocytes synthesize the myelin sheath that covers the neuron axons. Myelin is the layer of fat that protects the axon and makes possible the transmission of nerve impulses from one neuron to the next. The neuroglia also helps to maintain the reactive properties of nerve tissue in such conditions as post-traumatic scarring, inflammatory reactions, and oncogenesis.
The neuroglia, especially the oligodendrocytes, takes part in the generation of the slow, spontaneous bioelectric activity that is characterized by α waves on an electroencephalogram. Neurons and neuroglial cells form a unified functional and metabolic complex that operates in cycles and has an adaptive function. The complex has the capacity to shift certain metabolic processes predominantly to the neuronal or to the neuroglial elements, depending on the nature and intensity of the physiological and pathological condition of the CNS.
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| Schematic pictures showing all three cells that comprise the neuroglia: astrocyte, oligodendrocyte, and the microglia. |