Final answer:
The spinal nerves, dorsal root ganglia, somatic nerves, and cranial nerves are all parts of the somatic nervous system, a functional division of the peripheral nervous system involving motor and sensory fibers.
Step-by-step explanation:
Spinal nerves, dorsal root ganglia, somatic nerves, and cranial nerves belong to the somatic nervous system, which is a functional division within the peripheral nervous system. This system is composed of 12 pairs of cranial nerves and 31 pairs of spinal nerves. The somatic nervous system includes both motor and sensory fibers as well as the sensory ganglia, which encompasses the dorsal root ganglia and cranial nerve ganglia. The motor division carries messages from the central nervous system to internal organs and muscles, involving both the somatic and autonomic nervous systems.