Parasympathetic Nervous System
Original Post: Dr. Bruno, could you give me a lesson that I can understand on the parasympathetic nervous system, what it controls, and how polio may affect it, and if there is any advice for PSNS failure? My neurologist did testing and said the sympathetic nervous system tested ok but not the parasympathetic nervous system. My assumption is that it is probably polio related. Is that correct? Everything I find to read on the subject is a bit too technical and my eyes glaze over.
Dr. Bruno’s Response: Thank you for asking! Studying the sympathetic and the parasympathetic nervous systems is what I did at Columbia P&S and as the autonomic nervous system fellow at Presbyterian Hospital from 1977 to 1985. It's how I got interested in polio survivors with their cold and purple polio feet.
The poliovirus damaged both the sympathetic nervous system (causing polio feet) and the parasympathetic nervous system (causing constipation, difficulty swallowing, and fainting) in the portions of the brain stem that control their activity and the nerves themselves. It's much easier to test the parasympathetic nervous system (you can do it by taking someone's pulse for a minute while they breathe deeply) than it is to test the sympathetic side (for which you need expensive equipment).
Very simply the sympathetic nervous system is the gas pedal that turns your body on and is responsible for the "fight or flight response."
The parasympathetic nervous system, through your vagus nerve, is your body's brake, responsible for subduing the sympathetic nervous system (preventing your heart rate from going to 175 if you see a rattlesnake in front of you) and for activating your intestines and allowing you to absorb nourishment so that you have the energy to run away from the rattlesnake.
This is covered in more detail in The Polio Paradox.
2nd Post: So, the damage to the vagus nerve is actually through the parasympathetic nervous system, which is also damaged in some people? In other words, both are damaged if you have symptoms like rapid heart rate or lower heart rate?
Dr. Bruno’s Response: Vagus/parasympathetic and sympathetic centers are damaged in all polio survivors. The symptoms vary depending on the location and severity of the damage to brain stem.