Final answer:
The autonomic nervous system consists of the sympathetic and parasympathetic branches, distinguished by their anatomical origins in the spinal cord and brainstem, and by their opposing physiological 'fight-or-flight' and 'rest-and-digest' responses mediated primarily through norepinephrine and acetylcholine, respectively.
Step-by-step explanation:
The autonomic nervous system is divided into two primary branches: the sympathetic and parasympathetic nervous systems. These branches are distinguished both anatomically and physiologically. Anatomically, the sympathetic nervous system originates in the thoracic and lumbar regions of the spinal cord, while the parasympathetic nervous system stems from the brainstem and sacral region of the spinal cord. Sympathetic nerves are arranged in a way that allows for a wide-reaching, global response, often referred to as the 'fight-or-flight' response, which prepares the body for intense physical activity. On the other hand, the parasympathetic nervous system facilitates 'rest-and-digest' activities, promoting relaxation, digestion, and energy conservation.