Biosc&0150:&Foundations&of&Biology&I.& & Review&12:&Chapter&45&46& &Adel,&Anthony,&Megan,&Dr.&Swigonova& & Page&1&of&5&Review&Chapter&45:&Electrical&signals&on&animals&&1. What&ions&are&responsible&for&the&depolarization&phase?&The&repolarization&phase?&Which&way&the&ions&flow&relative&to&the&cell?&Na+&ions&in&depolariz at io n ,&K+&in&repolarization ;&Na+&flows&into&the&cel l&for&depolarization,&K+&flows&out&of&the&ce ll &fo r&r ep o la ri za tio n&a. With&regards&of&sodium&and&potassium&channels,&explain&why&i. Positive&feedback&occurs&in&the&open ing &of&Na+&channels.&Na+&channels&open&w h en &the&cell&membrane&depola rizes,&an d&as &mo re&ch an nels &op en,&m ore &Na+&flows&into&the&cell,&further&depolarizing&the&cell,&causing&more&voltageJgated&Na+&channels&to&open&ii. Na+&stops&flowing&across &a&me m bran e&d urin g&an &actio n&p ote ntia l.&After&opening,&the&voltageJgated&Na+&channels&close&an d &te m p o ra ri ly&c an n o t&re o p en .&A l so ,&so d iu m &reaches&its&equilibriu m&potential,&so&not&n et &fo rc e&i s&a va il a bl e&t o&d r ive &N a+&movement.&iii. K+&channels&start&op en in g.&K+&channels&open&in &re sp o n se &to &m e mbrane&depolarization&b. Explain&why&the&action&potential&is&an&all&or&none&phenomenon.&Once&the&threshold&level&of&depolarization&is&attained,&the&probability&that&the&voltageJgated&sodium&channels&will&open&approaches&P=100%.&But&below&threshold,&the&massive&opening&of&Na+&channels&does&no t&occur,&P=0%.&c. Predict&what&would&happen&if&sodium&channels&continued&to&open&once&membrane&depolarization&was&complete.&Na+&would&continue &to &m o ve &in to &t he &ce l l&a s&vo l ta ge Jgated&K+&channels&opened&and&potassium&began&to&diffuse&out&of&the&cell.&As&a&result,&repolarization&would&take&much&longer.&&d. Multiple&Sclerosis&is&a&disease&resulting&in&damage&to&myelin&sheath.&Explain&why&the&disease&leads&to&impaired&electrical&signalin g.& Myelin&sheath&acts&as&a&type&of&electrical&insulator.&As&charge&spreads&down&an&axon,&myelin&sheath&prevents&ions&from&leaking&back&out&across&the&plasma&membrane&of&the&neuron.&In&myelin&degenerates,&the&transmission&of&electrical&signals&slows&considerably.&&&2. Why&must&there&be&an&indirect&mechanism&that&transmits&electrical&signals&from&cell&to&cell&across&their&plasma&membranes ?&The&cytoplasm&of&most&neurons&is&not&directly&connected&to&the&cytoplasm&of&other&neurons.&a. Explain&the&steps&of&synaptic&transmission.&An&action&potential&reache s&t h e&e n d &of &th e &ax o n&and&the&depolarization&made&by&the&action&potential&opens&voltageJgated&calcium&channels&near&the&synapse.&An&electrochemical&gradient&is&made&favoring&the&inward&flow&of&Ca2+&through&the&channels.&Th e&increased&concentration&of&calcium&inside&the&axon&causes&synaptic&vesicles&to&fuse&with&the&membrane&and&release&neurotransmitters&into&the&synaptic&cleft.&Neurotransmitters&bind&to&receptors&on&the&postsynaptic&cell,&leading&to&changes&in&the&membrane&potential&which&may&cause&another&action&potential.&The&process&ends&as&the&presynaptic&cell&takes&back&the&neurotransmitter.&&b. Suppose&there&was&a&drug&that&permanently&closed&the&calcium&channels&in&neurons.&What&would&be&the&result?&Though&the&depolarization&from&the&action&potential&may&set&up&an&electro&chemical&gradient,&because&the&calcium&channels&are&closed&off,&synaptic&vesicles&will&Biosc&0150:&Foundations&of&Biology&I.& & Review&12:&Chapter&45&46& &Adel,&Anthony,&Megan,&Dr.&Swigonova& & Page&2&of&5&not&be&able&to&respond&by&binding&to&the&membrane&to&release&neurotransmitters,&effectively&stopping&any&signals&from&occurring.&c. Why&do&you&think&it&is&efficient&for&neurons&to&reuptake&neurotransmitters&rather&than&releasing&them&and&creating&ne w&o ne s? & Reuptake&is&necessary&because&it&allows&for&the&recycling&of&neurotransmitters &and &regu lates &the&lev el&of&n euro tran sm itte r&present&in&the&synapse&and&controls&how&long&a&signal&resulting&from&neurotransmitter&release&lasts.&Also,&neurons&are&constantly&sending&signals&so&if&neurons&had&to&keep&making&new&neurotransmitters&in&order&to&send&a&signal,&it&would&be&a&lot&harder&and&longer&for&signals&to&actually&occur.&&3. Would&you&expect&the&neurotransmitter&acetylcholine&to&bind&to&the&same&site&on&the &re ce p to r&molecule&as&dopamine&would?&Probably&not&because&neurotransmitters&are&ligands&that&bind&to&specific&sites&on&receptor&molecules.&So&acetylcholine&has&its&own&site,&as&does&dopamine.&a. Explain&what&is&meant&by&neurotransmitter&signals&being&transduced&from&chemical&to&electric&signals.&When&a&neurotransmitter&binds&to&a&ligandJgated&ion&channel&in&the&postsynaptic&membrane,&the&channel&opens&and&admits&a&flow&of&ions&along&an&electrochemical&gradient&so&there&is&a&change&in&the&membrane&potential&of&the&post&synaptic&cell.&&b. Why&might&it&be&that&the&use&of&cocaine&causes&“hyper”&state&for&the&user?&Cocaine&prevents&the&reuptake&of&dopamine&so&it&is&in&the&synapse&between&the&pre&and&postsynaptic&cell&longer&so&it&can&bind&to&the&posts yna ptic &me m bra ne&co m p letely &with ou t&be ing &taken &ba ck&again.&&c. What&are&EPSPs&and&IPSPs?&Excitatory&postsynaptic&potentials&(EPSPs)&are&changes&in&the&postsynaptic&cell&that&make&action&potentials&more&likely&to&happen&while&inhibitory&postsynaptic&potentials&are&the&opposite.&d. Explain&what&is&meant&by&“summation”&in&postsynaptic&neurons.&EPSPs&and&IPSPs&cancel&each&other&out,&however&if&there&are&sever&EPSPs&occurring&together,&they&add&up&and&make&the&neuron&much&more&likely&to&fire&and&action&potential.&&e. Ethanol&was&once&used&as&an&anesthetic&before&drugs&such&as&morphine&and&novacane&were&invented.&Why&is&ethanol&considered&to&be&an&anesthetic?&Ethanol&mimics&the&response&o f&GABA,&which&is&considered&an&IPSP,&which&is&inhibitory.&Because&it&is&inhibitory,&if&someone&is&in&pain,&it&would&be&able&to&preven t&the&b rain &from &sen d ing&sig na ls&ind ica ting &pain ,&thus &it&is&a&sedative.&&4. What&would&happen&to&the&membrane&potential&(J65&mV&at&resting)&under&each&of&the&following&conditions?&a. flooding&the&outside&of&the&cell&with&ClJ:&&the&membrane&potential&would&be&smaller&because&the&charge&on &the&outside&of&the&membrane&would&become&increasingly&negative,&making&the&relative& potentials& between& the& inside& and& outside& of& the& memb rane & closer& in& charge& and&decreasing&membrane&potential.&&&b. flooding&the&outside&of&the &cell&with&Na+&:&&the&memb r a n e &poten t ia l&wou