If a stressful situation occurs the sympathetic system prepares the body for action by increasing the heart beat, dilating blood vessels in the muscles, dilating the bronchioles in the lungs for more oxygen whereas the Parasympathetic Nervous system kicks in once the situation is over and returns the heart beat and breathing etc back to normal.
The sympathetic system has a thoraco- lumbar outflow from the spinal cord to relay in the ganglia adjacent to the spinal cord which then pass fibres to organs like the heart, intestine, adrenal glands and blood vessels. This system releases adrenaline and noradrenaline to produce the fight or flight reaction. The Parasympathetic