The central nervous system makes up most of the human nervous system. The central nervous system is responsible for receiving input from, and coordinating the movements of, all parts of the body. In this system, clusters of cell bodies are called nuclei.
The peripheral nervous system is responsible for connecting the central nervous system to the body's extremities. In this system, clusters of cell bodies are called ganglia.
Nuclei are the most common arrangements of neurons in the body. For example, the structures of the brain called the thalamus and the hypothalamus are made up entirely of nuclei. These clusters of cell bodies make up most of the "grey matter" in the brain.
Ganglia string together to form a "plexus." Ganglia are the pathways for signals between neurons in the central nervous system, or nuclei, and other parts of the body.