All neurons have a prominent soma, or body to the neuron. The soma contains the essential functions of the cell, include the nucleus which holds the neuron's DNA.

One way in which neurons are catagorized is by the number of projections, or poles, on the soma. Projections may be either the dendrites, which receive impulses, or the axon, which transmits them to adjacent neurons. There are four basic classes of neurons based on these factors: