BIPN 144 Week 9 Notes(part 2)

BIPN 144 Week 9 Notes(part 2) - BIPN144Week9Notes(Part2)

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Unformatted text preview: BIPN144Week9Notes(Part2) Note:ThishasnotbeenreviewedbyDr.Bierandmayhaveerrors.Always trusttheprofessoroverthesenotes. Dr.BierstartedoffthelecturebydiscussingthefinalNeuromuscularjunction experiment.Inthisexperimentalidocainecollarwasplacedaroundtheinnervating nerveaxon.Lidocaineblockselectricimpulses,butnotchemicalfactors,andaswith theotherexperiments,thisleadtoanincreaseinextrajunctionalreceptors.The samewastruewhenthenervewastreatedwithcurare.Andwhenthesystemwas denervated,butstimulatedelectrically,thenumberofERJ'sdecreased. Dr.Bierthenspokebrieflyabouthownervescanhelptoshapethemusclefibersto whichtheyconnect.Typically,fastnervesconnecttofastmuscleandslownerves connecttoslowmuscle,howeverifyouhookafastnervetoaslowmuscle,the musclebecomesafastmuscle,andlikewiseaslownervemakesafastmuscleintoa slowmuscle.I'mafraidIdon'thaveanymorespecificsonthis,andhonestlyitdidn't seemthatimportant,butIhadnotedit,soIthoughtI'dincludeitinthesenotes. Dr.Bierthenstartedtalkingaboutcoincidencedetection.Developingnervesare verycompetitive.They'relikethatguythatneverworkedouthishighschoolsports issues,andtreatsevenfriendlyfamilygamesoftouchfootballsoseriouslythat GrandpaMiltonendsridinghomefromThanksgivinginanambulance.Competitive. SoifnerveAandnerveBarecompeting,andAregularlyfiresbeforeB,thenAwill win.However,ifbothneuronsfireatexactlythesametime,thentheydonot compete,andbothwin!Remember,inearlydevelopment,anexcessofpresynaptic cellswereproduced.Thismeansthattherearemoreneuronsthantargets.These neuronsfightitouttoseewhogetstoinnervateandwhowillbeeliminated!Early on,targetsarepolyinnervatedandpresynapticneuronshavemultiplebranches. Aftersometimehaspassed,theseareprunedawaysothattherearefewerpost synapticcontactsandfewerbranches. Hethendiagramedanexperimenttoillustratethisprinciple.Intheexperiment,2 neuronswereapproachingthesamemusclefiber.Electrodeswerehookeduptothe neuronstomakethemfireondemand.Iftheywerefiredasynchronously,thenonly oneneuronsurvived.Iftheywerefiredsimultaneously,thentheybothsurvived!(In thecaseofmotorneuronsandmusclefibers,thisdoublenerveattachmentdoesnot occurinnature,butitdoeshappeninotherpartsofthenervoussystem. Hethenbrieflymentionedthatpresynapticcellscanreinforcepostsynapticcells. Postsynapticcellscanlikewisereinforcepresynapticcells. Inpassing,hementionedthewhiskerbarrelexperiment.Thewhiskerbarrelisa sensoryorganonrats.Theycutthewhisker,andtheareathatusedtobeinnervated bythatsensoryorgan,wasinvadedbythesurroundingwhiskerbarrelnerves.He alsopointedoutthatthereisconstantcommunicationacrossthesynapseand competitioninthesurroundingareasasdemonstratedbythehalfretinal experimentandthegrowingfisheyeexperiment. Dr.Bierthenexplainedthatelectricalactivityinatarget(ie.Amusclefiber)will reducetheproductionofsproutingfactorsthatinfluencetheinnervatingneuron. Inalaterstagedsystem,theremovalofaninnervatingneuroncansometimeslead tothedeathofthetarget!(Butinearlystages,targetscan(andmust)survive withoutinnervation). ThenDr.Bierstartedtalkingaboutthedevelopmentofoculardominancecolumns. Invertebrates,theneuronsfromtheretinaprojectbackintothevisualcortexina binocularmanner.Intheadultanimal(oratleasttheadultcat)theseprojections linkuptothevisualcortexinasortofstripedpattern.Thisstripedpatterndevelops astheyoungretinasbeginrespondingtolightandsendimpulsesdowntheirnerves tothevisualcortex.Thenervesfromthetwodifferenteyescompetewitheach other.Ifaneuronfromeacheyeisfiringonthetargetinunison,thenbothwill survivetoinnervatethatareaofthevisualcortex.If,however,theyarefiringat differenttimes,thentheywillcompete.Groupsofcellsfromthesameeye,willbe stimulatedandfireatnearlythesametime.Thesewillcompetewithgroupsofcells fromtheothereye.Thiscompetitionleadstotheformationofstripes,whereone stripeispredominantlyinnervatedfromoneeye,andthenextadjacentstripewill bepredominantlyinnervatedbytheothereye. Inafrogthereisusuallynobinocularvision.However,ifathirdeyeisgraftedin earlyindevelopment,thenyougetascenariowheretwoeyesinnervateonetectum. Thisresultsincompetitionbetweenthenervesofthetwoeyes,resultinginthe formationofoculardominancecolumns!(justlikeinthecat)!Somescientists noticedthattherearesomeweakstripesevenbeforetheretinashavebeenexposed tolight.Theseareattributedtospontaneouswavesofcalciumspreadingacrossthe retinas.Inthiscase,cellsclosetogetherwillfireataboutthesametime,andcells thataredistantwillfireasynchronously. ...
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