It was not until 1921 that the physiologist Langley published h i famous textbook in which he conceptualized and formalized the idea an autonomic (autonomous) nervous system. He also suggested th I the autonomic nervous system was made up of not two but thr< components—the sympathetic, parasympathetic, and enteric nervoi systems. He defined the latter as being comprised of the vast system nerve cells that resides in the wall of the gut (by definition, the enti digestive tube from the oral cavity to the anus). Although Langlt publicized his ideas widely, only the idea of the sympathetic an io. rtjaxa non am) mojiia /'/OA $M
parasympathetic components caught on, and the concept of an enteric nervous system was either forgotten or was simply included conceptually as a part of the parasympathetic nervous system. Finally, however, after the idea had languished for six decades, biologists started seeing in the 1980s that the enteric system was indeed an independent nervous system just as complex, with just as many neurotransmitters, and with even more neurons, than the spinal cord itself—a veritable "second brain" within the gut, one which is not only important to digestive system function but one that is probably important for the experience of many emotions. The story of this system has just begun, and textbooks that continue to ignore it will soon be obsolete.
Langley actually commented in his 1921 text that the enteric nervous system was probably more truly autonomous than either the sympathetic or parasympathetic systems. And neuroscientists ultimately found this to be correct. We now know that the enteric nervous system is capable of supervising the digestion of food, the propulsion of food through the bowel, and management of all other bowel functions, even when all nerve connections from the brain and spinal cord have been experimentally severed. This system is almost certainly important to relaxation, although attempting to say exactly how would be premature. Emotional connections may catch the attention of experimental psychologists in time, but it's anyone's guess.
So in summing up the widely disparate ways in which the nervous system affects relaxation, we see that several separate but related pictures emerge, one relating to muscular relaxation and the somatic nervous system (which we discussed earlier in this chapter as well as in chapter 1 and 2), another to the sympathetic nervous system, another to the parasympathetic nervous system, and possibly yet another to the enteric nervous system. First of all, relaxation requires skeletal muscular relaxation, and it requires that the sympathetic nervous system be quieted down. There is no way you can relax if you are fidgeting (somatic system) or if you arc in the middle of a flight-or-fight response (sympathetic system). And second, before you do a relaxation, your activities and behaviors should be adjusted so that the parasympathetic and enteric nervous system are not overly burdened with housekeeping tasks that draw attention to themselves and prevent relaxation—tasks such as digesting a large meal or coping with constipation, diarrhea, a full bladder, asthma, menstrual cramping, or sexual excitation. And finally, if the purported emotional content of the enteric nervous system grips you with regrets for the past, anxiety for the future, fear of the unknown, or an overly joyful mood in the present, relaxation will be impossible. Let it go; it's useless for relaxation.
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