neuroscien part 3 exam 2


An Action potential in axon


-signal for sending information over distances along axons-all or none,peaks~40ml-doesn't diminish in size (different from EPSP in dendrite)-same duration,~1msec


From 0mv to -80mv by opening K+ channels


a all channels closedb K+ channels open Gk>0 vm negativec equlibrium potential vm =Ek=-80 no net K+ currentd staring at vm=Ek=-80 gk>>gNae Na+channels open gNa>>gK vm more postive (rising phase) close to Enaf Na+ channels close gK>>gNa (falling phase) k+ outg resting membrane restored gK>>gNaf


Voltage gated sodium channels


-one long polypeptide -fomer domains (I-IV)-form a pore-each domain has six transmembrance helices (s1-s6)


Voltage sensor


s4 helic positively charged amino acids


What happens when vm at -40mv or above ?


-voltage sensor moves -chemical changes conformation-pore opens up


Selectivity filter


-partially hydrated Na+ions fit -patially hydrated K+ ion are too large


Patch clamp technique


-glass pipette forms a tight seal w/ membrane-used to record the current through single ion channels


Patch clamp recording of voltage gated sodium channel which are?


-depolarize membrane to -40mv-inward current-inactivate quickley, can't open again before reture to rmp-local anaesthetics blcok voltage gated Na+ channels


steps of voltage gated sodium channels


1 at -65 mv channel closed2 membrane voltage =-40mv channel opens3 inactivation by gloloular portaion of proton (ball)4 pore closes when voltage is -65mv ball is away


Many different kinds of potassium channels


1 leak channels open all the time2 voltage gated K+ channels(delayed rectifiers)-open w/ delay-outward current -contribute to falling phase of action potential (together w/ leak channels)different time scale then sodium


How sodium and potassium channels produce an action potential?


-Na+ channels open immediately when voltage reaches threshold -inward Na+ cuurrent brief b/c Na+ channels inativate-delayed recitfiers (voltage gated K+ channels open w/ delay -outward K+ current-brief inward current followed by delayed outward current


Action potential conduction down axon


positive charges spread causing membrane just ahead to depolarize and reach thresholdaction potential only propagates in one direction b/c retractoryperiod-Na+ channels inactivated until membrane potential returns to rest


myelin and nodes of ranvier


positive charges spread futher w/ myclinvoltage gated Na+ channels are only present in nodes of ranvier


saltatory conduction


Saltatory means "skipping", action potential skips from on node of ranvier to another-speeds up action potential conduction b/c it doesn't have to be regenerated as often-saves energy Na/K pump restores ion concentration gradients after each action potential