Final answer:
A nucleus is the term for a localized collection of neuron cell bodies in the central nervous system (CNS), while a ganglion is the term for the same in the peripheral nervous system (PNS). These structures are clearly defined groups of neurons and are smaller than a nucleus.
Step-by-step explanation:
A localized collection of neuron cell bodies in the central nervous system (CNS) is called a nucleus, while in the peripheral nervous system (PNS), it is called a ganglion.
Nuclei and ganglia are smaller than a nucleus and are clearly defined groups of neurons found in specific anatomical structures. For example, there is a group of nuclei in the CNS called the basal nuclei or basal ganglia. These terms help differentiate between central and peripheral structures.