Final answer:
In the CNS, a cluster of neuron cell bodies is called a nucleus, while in the PNS, it's referred to as a ganglion.
Step-by-step explanation:
In the central nervous system (CNS), a localized collection of neuron cell bodies is known as a nucleus. This term has various meanings in anatomy and physiology, such as the center of an atom or a cell, but within the CNS, it specifically refers to a functional center made up of neuron cell bodies. On the other hand, the peripheral nervous system (PNS) contains structures called ganglia (singular: ganglion), which are clusters of neuron cell bodies situated in the periphery.
Ganglia can be sensory or autonomic, with the dorsal root ganglion being a common type associated with sensory nerves extending into the CNS. Nerves and ganglia are found throughout the body and serve as the main structures of the PNS, with ganglia acting as gray matter and nerves as white matter. The term 'ganglion' was historically used within the CNS to describe a group of nuclei known as the basal ganglia, but modern usage typically reserves 'ganglion' for peripheral structures, referring to the central structures as 'basal nuclei' to avoid confusion.
In summary, the CNS and PNS are distinguished not only by their functions but also by the terminology used to describe their structure: Nuclei in the CNS and ganglia in the PNS.