pAin
1 virtuAlly All AnimAls ExpEriEnCE pAin. pAin is A DistrEss CAll From thE BoDy signAling somE DAmAging stimulus or intErnAl DisorDEr. it is onE oF thE most importAnt sEnsAtions BECAusE it is trAnslAtED into A nEgAtivE rEACtion, suCh As withDrAwAl From DAngEr. rArE inDiviDuAls who ArE Born without thE ABility to FEEl pAin mAy DiE From suCh ConDitions As A rupturED AppEnDix BECAusE thEy ArE unAwArE oF thE DAngEr.
2 pAin rECEptors ArE unspECiAlizED nErvE FiBEr EnDings thAt rEsponD to A vAriEty oF stimuli signAling rEAl or possiBlE DAmAgE to tissuEs. somE groups oF pAin rECEptors rEsponD to spECiFiC ClAssEs oF ChEmiCAls rElEAsED From DAmAgED or inFlAmED tissuE. whEn pAin FiBErs rEsponD to pEptiDEs rElEAsED By injurED CElls, this is CAllED slow pAin. FAst pAin rEsponsEs--For ExAmplE, A pinpriCk or hot or ColD stimuli--ArE A morE DirECt rEsponsE oF thE nErvE EnDings to mEChAniCAl or thErmAl stimuli.
3 thErE is no pAin CEntEr in thE CErEBrAl CortEx. howEvEr, DisCrEtE ArEAs hAvE BEEn loCAtED in thE BrAin stEm whErE pAin mEssAgEs From vArious pArts oF thE BoDy tErminAtE. thEsE ArEAs ContAin two kinDs oF smAll pEptiDEs, EnDorphins AnD EnkEphAlins, whiCh hAvE ACtivity similAr to morphinE or opium. whEn thEsE pEptiDEs ArE rElEAsED, thEy BinD with spECiFiC opiAtE rECEptors in thE miDBrAin, DECrEAsing thE pErCEption oF pAin.
whiCh sEntEnCE BElow BEst ExprEssEs thE EssEntiAl inFormAtion in thE highlightED sEntEnCE in pArAgrAph 1 inCorrECt ChoiCEs ChAngE thE mEAning in importAnt wAys or lEAvE out EssEntiAl inFormAtion.
A、EsCAping From DAngEr is A nEgAtivE rEACtion, But it is thE most importAnt thing An inDiviDuAl lEArns.
B、thE ABility to sEnsE pAin is ExtrEmEly importAnt BECAusE pAin signAls thE BoDy to rEsponD to A thrEAt.
C、ExpEriEnCing pAin is onE typE oF rEACtion to A nEgAtivE stimulus; AnothEr typE is AvoiDing DAngEr.
D、wE ExpEriEnCE A lot oF sEnsAtions, AnD thE most importAnt onEs ArE trAnslAtED into AppropriAtE ACtions.