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Neuroglial or glial cells, make up one of the two major cellular components of nervous tissue (the other being neurons). Nervous tissue is composed of almost 10 times as many glial cells as neurons. They primarily provide structural and metabolic support for neurons, some aid in communication between neurons and assist in neurological development, while others respond to damage and pathogens. Glial cells are divided into two major classes of cell types: microglia and macroglia. The microglia are primarily phagocytes, they are mobilized by minor pathological changes and can eliminate invading microorganisms, promote tissue repair, and remove debris.

Macroglia are separated into four classes: ogliodendrocytes, Schawnn cells, astrocytes, and ependymal cells. Schwann cells and ogliodendrocytes form the myelin sheath around neuron axons. This sheath insulates the electrical impulse that travels down the axon, but also increases the speed of the electrical propagation by keeping unmylinated spaces along the axon. The impulse jumps between these unmylinated zones called the nodes of Ranvier. This form of propagation is referred to as saltatory conduction. Schawnn cells myelinate the peripheral nervous system while ogliodendrocytes myelinate the central nervous system. Schawnn cells and ogliodendrocytes also help guide axon growth during neurological development. Astrocytes are important in providing structural support and also aid in metabolic functions. During development of the nervous system, astrocytes serve as scaffolding for axons as they grow. Enpendymal cells line the ventrical cavities in the central nervous system and produce cerebral spinal fluid and aid in regulating the flow of this liquid medium.


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