The momenta of individual objects changes. The total momentum remains constant. I have to disagree. If you have two cars that collide head on, the momentum of both vehicles stops. The ENERGY created by the impact causes usually, some reverse momentum but the momentum is lost.
As the SNS continues to trigger physical reactions, it causes a wear-and-tear on the body. It's not so much what chronic stress does to the nervous system, but what continuous activation of the nervous system does to other bodily systems that become problematic.
Figure 1. Overview of effects of the activation of (a) the sympathetic nervous system, where norepinephrine acts as the main neurotransmitter, and (b) the adrenomedullary hormonal system, where epinephrine acts as the main hormone.ympathetic nervous system. A major component of the autonomic nervous system. The main sympathetic neurotransmitter for cardiovascular regulation is norepinephrine. The main sympathetic neurotransmitter for sweating is acetylcholine.