The Autonomic Nervous System Divisions
The autonomic nervous system (ANS) houses two major divisions, the parasympathetic and the sympathetic division. At most times, the two divisions are antagonists to each other; if the sympathetic division causes excitation, the parasympathetic division will counter-act with an inhibitory effect. This is not always the situation, however. Because the two divisions may work independently, with some structures innervated by one division, and the two divisions may work synergistically, each contributing to one stage of a complex process. Generally speaking, the parasympathetic division is active in rest states, and the sympathetic division “kicks in” during times of exertion, stress, or emergency.
When you are doing a heavy weight lifting session at the gym your sympathetic division is full effect. It is sending signals to your cardiovascular and respiration center of the pons, leading to increased blood pressure, heart rate, breathing rate and depth of respiration, so blood and oxygen delivered to muscles. All of this happens unconsciously; it is and is an involuntary action. During this time also, your digestive system is somewhat inhibited so all of ones energy can be focused at the task at hand. One will also have an increased mental alertness and a state of euphoria. Also, there is a general elevation of muscle tone, so a person looks tense. Finally, the mobilization of energy stores, through an increased breakdown of glycogen in muscle and liver cells and the release of lipids from adipose tissues.
After the workout or cardio session the activity of the sympathetic nervous system decreases and the parasympathetic division comes into play. When you leave the gym and step out into the bright sun (hopefully) the parasympathetic nervous system will cause a constriction of the pupils to inhibit the amount of light entering the eyes. And while on your way back home or wherever, there is secretion of digestive glands, including of hormones that promote nutrient absorption, so the hard worked muscles can recover properly. There is also a constriction of respiratory passageways and reduction in heart rate and force of contraction. All of this aids in you becoming more relaxed.
Like stated, the parasympathetic nervous system focuses on relaxation, food processing and energy absorption. It ahs been called the anabolic system because stimulation leads to a general increase in the nutrient content of th blood.
Kurt Kuhn - www.FUSIONBodybuilding.com