Hockenbury Discovering Psychology 5th txtbk

58 CHAPTER 2 Neuroscience and Behaviorsympathetic nervous systemBranch of the autonomic nervous system thatproduces rapid physical arousal in response toperceived emergencies or threats.However, the autonomic nervous system is not completely self-regulating. Byengaging in physical activity or purposely tensing or relaxing your muscles, youcan increase or decrease autonomic activity. Emotions and mental imagery also influenceyour autonomic nervous system. Vividly imagining a situation that makesyou feel angry, frightened, or even sexually aroused can dramatically increase yourheart rate and blood pressure. A peaceful mental image can lower many autonomicfunctions.The involuntary functions regulated by the autonomic nervous system are controlledby two different branches: the sympathetic and parasympathetic nervoussystems. These two systems control many of the same organs in your body but causethem to respond in opposite ways (see Figure 2.9). In general, the sympatheticnervous system arouses the body to expend energy, and the parasympathetic nervoussystem helps the body conserve energy.The sympathetic nervous system is the body’s emergency system, rapidly activatingbodily systems to meet threats or emergencies. When you are frightened, yourbreathing accelerates, your heart beats faster, digestion stops, and the bronchial tubesin your lungs expand. All these physiological responses increase the amount of oxygenavailable to your brain and muscles. Your pupils dilate to increase your field of vision,and your mouth becomes dry, because salivation stops. You begin to sweat in responseto your body’s expenditure of greater energy and heat. These bodily changes collectivelyrepresent the fight-or-flight response—they physically prepare you to fight or fleeSympathetic Nervous SystemParasympathetic Nervous SystemEyes:Pupils dilateMouth:Inhibits salivationLungs:Bronchi dilate:rapid, shallowbreathingHeart:Increases heartbeatPalms:Stimulates sweat glandsStomach and intestine:Inhibits digestion#@!!#! Red touches yellow,you’re a dead fellow!Eyes:Pupils contractMouth:Stimulates salivationRed touches black,you’re okay, Jack.Palms:Sweat diminishesLungs:Bronchi constrict:slower, deeper breathingHeart:Slows heartbeatStomach and intestine:Stimulates digestionFigure 2.9 The Sympatheticand Parasympathetic Branches ofthe Autonomic Nervous SystemHikers in the southern UnitedStates memorize a simple rhymeto distinguish the venomous coralsnake (red stripes touch yellowstripes) from its harmless mimic,a scarlet king snake (red stripestouch black stripes). Arousal ofthe sympathetic nervous system(left) prepares the hiker to fightor flee the dangerous snake.When the hiker realizes that thesnake is harmless (right), theparasympathetic nervous systemcalms the body and graduallyrestores normal functioning.