Final answer:
Clusters of neuron cell bodies outside the CNS are called ganglia, and axons travel together in bundles called nerves. These terms specifically indicate their location within the Peripheral Nervous System as opposed to nuclei and tracts in the Central Nervous System.
Step-by-step explanation:
Outside the Central Nervous System (CNS), clusters of neuron cell bodies are called ganglia and axons travel together in bundles called nerves. While in the CNS, similar structures are given different names; a group of neuron cell bodies is known as a nucleus, and a bundle of axons is referred to as a tract. The distinction in nomenclature between these structures highlights whether they are part of the CNS or the Peripheral Nervous System (PNS).
In both the CNS and PNS, the naming of neuron collections and axon bundles is anatomically specific to signal their location and possibly their function. For example, sensory ganglia contain unipolar neurons and are located on the dorsal root of all spinal nerves as well as with many cranial nerves. Axons can exist as part of both nerves and tracts, with the specific term used depending on whether they are in the PNS or CNS, respectively. An example of this is how the axons that leave the retina are called the optic nerve in the PNS, but when they enter the cranium and become part of the CNS, they are termed the optic tract.