Nissl body
(Nissl substance, Nissl material)
A large granular body found in neurons. They are of rough endoplasmic reticulum (RER) with rosettes of free ribosomes, and are the site of protein synthesis.
They can be demonstrated by Nissl staining to stain extranuclear RNA granules in blue, localizing the cell body, as it can be seen in the soma and dendrites of neurons, though not in the axon or axon hillock.
They represent the protein-synthetic machinery of the cell. Rough ER is evident in the soma and proximal reaches of dendrites, wherein it mainly appears as branching and anastomosing tubules and short cisternae. It is not seen in the axon hillock, nor in the axon itself, which contains only agranular reticulum. The soma is the major site of protein synthesis.