The physiology of TMS begins in the brain. Here repressed emotions like anxiety and anger set in motion a process in which the autonomic nervous system causes a reduction in blood flow to certain muscles, nerves, tendons, or ligaments, resulting in pain and other kinds of dysfunction in these tissues. The autonomic nervous system is a subsystem of the brain that has the responsibility for controlling all of the body's involuntary functions. It determines how fast the heart beats, how much acid is secreted into the stomach for digestive purposes, how rapidly one breathes, and a host of other moment-to-moment physiologic processes that keep our bodies functioning optimally under everyday circumstances or in emergencies. The so-called fight or flight reaction that all animals share, particularly important in lower animals, is directed by the autonomic system. In order to meet the emergency, every organ and system in the body is properly prepared. For some systems it means total cessation of activity so that the body's resources can be mobilized to deal with the danger more effectively. Typically, most of the body's nutritive and excretory activities are shut down, the heart beats more rapidly, and blood is shunted away from less important functions so as to be available in larger quantities for systems that are crucial to escape or fight, like the muscles. The critical importance of the autonomic system of nerves is obvious.