Final answer:
The defecation reflex is mediated by the sympathetic, parasympathetic, and enteric nervous systems, which are part of the autonomic nervous system responsible for controlling visceral functions including those of the digestive organs.
Step-by-step explanation:
The three nervous system components that mediate the defecation reflex are the sympathetic, parasympathetic, and enteric nervous systems. These components are part of the broader autonomic nervous system, which also has a direct role in controlling the digestive system. The autonomic nervous system, which includes the sympathetic and parasympathetic divisions, provides unconscious control over visceral functions.
The enteric nervous system is responsible for the direct control of the functions of the digestive organs, sometimes without CNS involvement. It is capable of mediating reflexes such as peristalsis and the defecation reflex through myenteric plexuses within the digestive tract. The defecation reflex involves a coordination between these autonomic divisions and the enteric nervous system, which can operate independently but is also subject to modulation by the central nervous system through fibers such as those in the vagus nerve.