The autonomic nervous system is divided into two parts. They are the sympathetic nervous system (SNS) and the parasympathetic nervous system (PSNS). Sometimes the enteric nervous system is also considered part of the autonomic nervous system as well.
The sympathetic nervous system responds to the bodies "fight or flight" response. Say for example you walking to your vehicle after leaving the mall and a stranger approaches and tries to grab you. You have to make a quick decision-do you fight or run? Your body is using energy. Your heart rate increases, your blood pressure increases, and your digestive system slows down. It basically uses the body's resources when it is under stressful situations.
The parasympathetic nervous system works to save and conserve energy. For example, you are outside on a nice warm day and you decide that it is time to relax. Your heart rate decreases, your blood pressure decreases, and digestion speeds up.
The sympathetic and parasympathetic nervous systems essentially have actions that oppose each other. They are both branches of the ANS(autonomic nervous system). The sympathetic system is called the "fight or flight" nervous system because neuronal pathways elicit a response that prepares the body to run or fight. It is also active when you experience extreme emotions like great joy,excitement,anxiety,fear, or anger. The neurons innervate anatomical structures like the eyes,salivary gland,heart,stomach,colon, and bladder. The parasympathetic system also innervates the same structures but in a very different way. The PS system is in control of our normal, everyday,mundane actions. In other words, when we are not excited, angry etc., the PS system is in control.
The sympathetic nervous system is the system that induces fight or flight response, activates bodily resources like adrenaline, etc. in times of stress. But it is also the system that maintains a basic level of homeostasis during non-stressful times as well, regulating various body functions to maintain that balance while the body is awake and active.
The parasympathetic nervous system appears to have similar functions as it controls some functions like cardiac function and that of other smooth muscles but it does so while the body is at rest, or while performing functions like digestion, etc. It works together with the sympathetic nervous system as it triggers reactions that do not require an immediate response like the fight or flight reactions of the sympathetic nervous system.
Autonomic nervous system or internal life,vegetative system coordinates the activities of internal organs and autonomic functions of the body (nutrition, breathing, circulation, excretion, etc.).
Autonomic nervous system consists of two components which, are functionally antagonistic: sympathetic nervous system and parasympathetic nervous system, the first being a "consumer" and the second being the repairing one.
The two aspects of the neurovegetative system, which is the metabolic regulator, the sympathetic nervous system, which is the dynamic group and the parasympathetic nervous system, which is the anabolic group or relaxing group, are closely correlated with critical events which are evolving between activity (matter's wear) and standby (regeneration of matter). In functional terms, these two antagonistic systems work like pedals of a piano, which strengthens or suppress it sounds.