Motor neurons, which are the largest cells in the CNS, have a cell body measuring up to 135 microns. Granular neurons of the cerebellum, which are the smallest, measure 4 microns. The neuronal body balloons. The cytoplasm becomes smooth and the nucleus is displaced toward the periphery of the cell. This appearance, which is called central chromatolysis , is a reversible change that develops during repair of a neuron that has been disconnected from its target.
Neurons contain numerous mitochondria that are needed for aerobic energy production.
Deficiencies of mitochondrial enzymes affect primarily the brain and muscle. In the brain, mitochondrial disorders cause neuron loss and present as encephalopathy, myoclonus, strokes, and other clinical disorders. Hypoxia, ischemia and hypoglycemia cause irreversible neuronal injury. Injured neurons shrink, become eosinophilic due to condensation of mitochondria, and their nuclei become pyknotic. Such neurons are referred to as anoxic neurons .