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NBME 23 Answers

nbme23/Block 2/Question#16 (66.5 difficulty score)
Which of the following best explains impaired ...
Increase in axonal capacitanceπŸ”

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submitted by mcl(599),
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nI esca you anwna og usepr rned nad ader uaotb ,elyimn tap,eaccanci adn asrtense,ci shti ygu sedo a gdoo ojb.

nwinkelmann  This really helped me, at least the pictures did. Here's my interpretation of the pictures in not super scientific terms: capacitance is like the "capaciy" to keep ions close to the membrane. Myelin puts a barrier between the ions in the conductive environment (ECF or ICF) and the nerve membrane. The higher the capacitance, the closer the ions are to the membrane, so it's like the charge effect is "more potent" so harder to change the membrane potentia, whereas if the ions are farther from the membrane, the charge effect is "less potent" so easier to change the membrane potential and thus easier to depolarize. Thus, with myelin, there is decreased capacity of the ions to be close to the membrane, so in demyelinating conditions, the ions can be really close to the membrane, i.e. higher capacitance. +22  
sweetmed  this helped a lot! +  
roaaaj  Well explained! +  
euchromatin69  or see u world 917 same concept +1  
brise  Uworld 1318*** +2  

submitted by visualninjacontender(17),
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ie-tm sntcnaot= netsasecRi x iCcaacaentp re -olw eimt nntaocts = eftras cnductoino nmi ey-l lowsre ncaeiccptaa - erethby erlngwio mite sttonnca dan rcnsigaeni cicontdnuo edesp lwo(er pcaaytic rof nreuon ot hold racegh may allow het grecha to p""umj fmor node ot doen - I amy eb inkmag atth last part pu tbu htat is hwo I rdtenasdnu )it

submitted by sympathetikey(1360),
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:reoScu pM/.nniid/kwo/sieyelrka.te:ith/giipw

ye"miln edspse the itnosnrsmsia of etllcrciae usilpesm lcdlae tocnai elisatpnto nalgo eatmdinlye aonsx by ngtsiinalu teh xano dna ucniegrd oxnala memernab eaccntaaipc"

littletreetrunk  I think this makes total sense, but how does it not ALSO stop fast axonal transport? +3  
laminin  axonal transport is transport of organelles bidirectionally along the axon in the cytoplasm since myelin is on the outside of the axon demyelination doesn't affect this process. source: "Axonal transport, also called axoplasmic transport or axoplasmic flow, is a cellular process responsible for movement of mitochondria, lipids, synaptic vesicles, proteins, and other cell parts to and from a neuron's cell body, through the cytoplasm of its axon." +3  
yotsubato  axonal transport is mediated by kinesin and dynein. Microtubule toxins like vincristine block these +3  
drdoom  @littletreetrunk "axonal transport" is movement of bulk goods via microtubules (which run from soma to terminus); ions, on the other hand, move in an "electrical wave" that we call an action potential! no axonal (microtubular) transport required! in other words, de-myelination will have no effect on the transport of bulk goods; but it will really mess up how fast "electrical waves" traverse the neuron! +  


AXONAL TRANSPORT. The directed transport of ORGANELLES and molecules along nerve cell AXONS. Transport can be anterograde (from the cell body) or retrograde (toward the cell body).

+6/- drdoom(884),

submitted by hello36654(5),
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so yhw si sesio"anct fo tfas lxaona tts"oarrpn rg?won to'nD etyenmdali xn,sao yb fditionei,n aveh atfs ennaoc?tcduc So emyeedtliadn asxon douwl evha nao"ietscs fo fats olanxa tno,tsarrp" whhci is eht snarew ,A t?irhg

diabetes  i think it slows down ,no cessation . +  
gdupgrant  Because fast axonal transport refers to the transport of vesicles containing neurotransmitters or some kind of cell product up and down microtubules in the axon. It isn't related to actual electrical signal transduction. +7