B. Astrocytes

In the brain, repair and glial scar formation is mainly accomplished by gliosis. (Formation of fibrous scar tissue does not generally occur in the brain.) Gliosis involves proliferation of astrocytes with formation of many glial processes. Some astrocytes become gemistocytic, i.e. they appear plump or swollen and the cytoplasm is eosinophilic.

C. Oligodendrocytes

Oligodendrocytes swell in response to almost any type of toxic or metabolic change. Diseases with primary involvement of oligodendrocytes result in disorders of myelin, with demyelination or abnromal myelin formation. The two major groups of diseases affecting oligodendrocytes and myelin are the leukodystrophies, which are usually inherited disorders of myelin metabolism, and the acquired demyelinating diseases. For example in multiple sclerosis, a demyelinating disease, oligodendrocytes and myelin degenerate in focal areas.

D. Microglia

Microglial cells become activated in response to injury and (a) assume the shape of a macrophage or (b) proliferate and adopt a rodlike form. Sometimes rod cells migrate around a dead neuron to phagocytize it, a process called neuronophagia; this cluster of rod cells is called a glial nodule or glial shrub and is common in viral infections.

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