1. It's all in the wiring. The nerves of the sympathetic division are connected to each other via ganglia (clusters of cell bodies) just outside the spinal cord in a chainlike fashion. This connection allows them to communicate and to work in synchrony. The release of norepinephrine engages a positive feedback mechanism that occurs with the sympathetic division and not the parasympathetic division. So, NE, once released (by sympathetic neurons), enhances the sympathetic response. On the other hand, the parasympathetic division does not have the ganglionic chain, so each component works separately and it is slower. Contrary to what some believe, they are not two phases, they are independent and interrelated mechanisms. Many behaviors can't occur without both systems acting simultaneously (urination is one that comes to mind).
2. One of the possible mechanisms is that light is detected by the suprachiasmatic nucleus of the hypothalamus, which then serves as a sleep-wake pacemaker. You don't need vision to be intact for that, although there does have to be a pathway from the retina to the SCN. In the absence of that connection, there are other things that reset the circadian rhythm each day although they aren't as good at it as light. Hope that helps. Carol Carol DeVolder, Ph.D. Professor of Psychology Chair, Department of Psychology St. Ambrose University Davenport, Iowa 52803 phone: 563-333-6482 e-mail: [EMAIL PROTECTED] -----Original Message----- Hi Tipsters-- I need to draw on your collective wisdom in order to answer the following student questions from my general psychology classes. 1) Why does the parasympathetic nervous system act more slowly than the sympathetic nervous system? 2) If light helps keep circadian rhythms on a 24hr schedule, what happens if the person is blind? Thanks, Julie -- Dr. Julie A. Osland, M.A., Ph.D. Assistant Professor of Psychology Wheeling Jesuit University 316 Washington Avenue Wheeling, WV 26003 Office: (304) 243-2329 e-mail: [EMAIL PROTECTED] --- To make changes to your subscription contact: Bill Southerly ([EMAIL PROTECTED]) --- To make changes to your subscription contact: Bill Southerly ([EMAIL PROTECTED])
