The parasympathetic branch is responsible for “rest and recovery” or relaxation responses. Activation of the parasympathetic nervous system decreases your heartbeat, relaxes your blood vessels and your muscles thus allowing blood to bring nutrients and carry waste away from your cells. Your digestive and elimination systems are stimulated and your breathing slowed down. Basically all the normal bodily responses associated with recovering, resting and “essential activities” you do when your life was not in danger.
The parasympathetic branch, centered in the adrenal cortex, uses the neurotransmitters acetylcholine (ACh), nitric oxide (NO), and cyclic guanosine monophosphate (cGMP) as its chemical mediators; this is the “rest-and-digest” arm of the autonomic nervous system. The particular nerve of the parasympathetic chain that supplies the heart with nervous activity is called the vagus nerve. The parasympathetic nervous system slows heart rate whereas the sympathetic nervous system increases the heart rate. It is well established that an imbalance in these two branches (autonomic balance) is present over time contributes to development of cardiovascular disease.