N eurons are the basic communicating units of the CNS 3966 . Their nuclei are large and vesicular, with a large nucleolus 3965 . Their cell bodies contain basophilic granules 3974 called Nissl substance, which represents rough endoplasmic reticulum. Naked nuclei without visible cytoplasm represent glial cells. 3967 Astrocytes have enlarged vesicular nuclei.
Oligodendrocytes have small dark nuclei and resemble lymphocytes.
Microglia have small, elongated nuclei without visible cytoplasm. Axons, dendrites, and glial processes cannot be seen, but this network of processes comprises the neuropil. It is particularly useful for looking at the neurofibrillary tangles and senile plaques of Alzheimer's disease 3970 . It is demonstrated using immunohistochemical techniques, and is useful for establishing the glial origin of a brain tumor. Cellular Responses to Injury Neurons Normal Histology N eurons are generally larger than glial cells.