Final answer:
The subdivision of the nervous system with a chain of two motor neurons, including preganglionic and postganglionic neurons, is the autonomic nervous system, which is divided into the sympathetic and parasympathetic nervous systems.
Step-by-step explanation:
The subdivision of the nervous system that consists of a chain of two motor neurons, comprising a preganglionic and a postganglionic neuron, is the autonomic nervous system. This system is a part of the peripheral nervous system and is subdivided into the sympathetic and parasympathetic nervous systems. The autonomic nervous system regulates involuntary bodily functions such as heart rate, digestion, and respiratory rate, and contrasts with the somatic nervous system, which controls voluntary movement.
The sympathetic nervous system prepares the body for stressful 'fight or flight' situations, while the parasympathetic nervous system is active during restful states, contributing to 'rest and digest' activities. On the other hand, the somatic nervous system, which is comprised of the sensory and motor nerves, is responsible for voluntary movements and the perception of environmental stimuli.