Hockenbury Discovering Psychology 5th txtbk

The Nervous System and the Endocrine System59Nervous systemFigure 2.10 Organization of theNervous SystemCentralnervous system(CNS)Peripheralnervous systemCarries messages toand from the CNSBrainSpinal cordConnects brainand peripheralnervous systemSomaticnervous systemControls voluntary musclesand transmits sensoryinformation to the CNSAutonomicnervous systemControls involuntarybody functionsSympatheticnervous systemArouses body toexpend energyParasympatheticnervous systemCalms body to conserveand maintain energyfrom a perceived danger. We’ll discuss the fight-or-flight response in greater detail inChapter 8, on emotion, and Chapter 12, on stress.Whereas the sympathetic nervous system mobilizes your body’s physicalresources, the parasympathetic nervous system conserves and maintains yourphysical resources. It calms you down after an emergency. Acting much more slowlythan the sympathetic nervous system, the parasympathetic nervous system graduallyreturns your body’s systems to normal. Heart rate, breathing, and blood pressurelevel out. Pupils constrict back to their normal size. Saliva returns, and the digestivesystem begins operating again.Although the sympathetic and parasympathetic nervous systems produceopposite effects, they act together, keeping the nervous system in balance (seeFigure 2.10). Each division handles different functions, yet the whole nervoussystem works in unison so that both automatic and voluntary behaviors are carriedout smoothly.The Endocrine SystemAs you can see in Figure 2.11 on the next page, the endocrine system is made up ofglands that are located throughout the body. Like the nervous system, the endocrinesystem involves the use of chemical messengers to transmit information from one partof the body to another. Although the endocrine system is not part of the nervous system,it interacts with the nervous system in some important ways.Endocrine glands communicate information from one part of the body toanother by secreting messenger chemicals called hormones into the bloodstream.The hormones circulate throughout the bloodstream until they reach specific hormonereceptors on target organs or tissue. Hormones regulate physical processesand influence behavior in a variety of ways. Metabolism, growth rate, digestion,blood pressure, and sexual development and reproduction are just some of theprocesses that are regulated by the endocrine hormones. Hormones are also involvedin emotional response and your response to stress.Endocrine hormones are closely linked to the workings of the nervous system. Forexample, the release of hormones may be stimulated or inhibited by certain parts ofthe nervous system. In turn, hormones can promote or inhibit the generation ofActivating the Sympathetic NervousSystem When the sympathetic nervoussystem activates in humans, tiny muscles inthe skin contract, which elevates your hairfollicles, producing the familiar sensationof “goose bumps” and making your hairstand on end. A similar process takes placein many mammals, making the fur or hairbristle, with rather spectacular results inthis long-haired cat.parasympathetic nervous systemBranch of the autonomic nervous systemthat maintains normal bodily functions andconserves the body’s physical resources.endocrine system(EN-doe-krin) System of glands locatedthroughout the body that secrete hormonesinto the bloodstream.hormonesChemical messengers secreted into thebloodstream primarily by endocrine glands.