Organization of Autonomic Nervous System
The autonomic nervous system (ANS) is the portion of the PNS that functions independently (autonomously) and continuously without conscious effort. This system transmits sensory information from visceral organs to the CNS and controls visceral functions by regulating the actions of smooth muscles, cardiac muscles, and glands. It regulates heart rate, blood pressure, breathing rate, body temperature, and other visceral activities that maintain homeostasis. Portions of the autonomic nervous system respond to emotional stress and prepare the body to meet the demands of strenuous physical activity.
The autonomic nervous system includes two divisions - the sympathetic and parasympathetic divisions. Some viscera have nerve fibers from each division. In such cases, impulses on one set of fibers may activate an organ, while impulses on the other set inhibit it. Thus, the divisions may act antagonistically, alternately activating or inhibiting the actions of some viscera.