Describe the function of the parasympathetic branch of the autonomic system and how it works in conjunction with the sympathetic branch

Question

What will be an ideal response?

Answer 1

The parasympathetic branch of the autonomic system is generally associated with the state of relaxation, and after a stressful encounter its activation serves to damp down the fight-or-flight response. As noted previously, the neurons of this system have their effect on their visceral targets through the use of the neurotransmitter acetylcholine. Most tissues of the viscera are innervated by both branches of the system. There are some exceptions; for example, the blood vessels and the adrenal medulla receive only sympathetic branch neurons.

Though it is common to think that only the sympathetic branch excites the organs (e.g., heart rate increase), that is a misconception. For example, it is the parasympathetic branch and not the sympathetic branch that excites the gastrointestinal system. The reason that some components of the viscera are excited by the sympathetic branch and others by the parasympathetic branch has to do with how the body's systems deal with threats to its survival. During normal resting non-stress periods it is more adaptive for the body to ingest food when needed, digest it, and store its energy. Without doing this, the body will not survive. However, during acute stress periods when there is imminent threat to survival, it is more adaptive to avoid ingesting food, stop digesting food previously ingested, and start mobilizing and expending energy. That is, to activate the fight-or-flight response.