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