neuroscien part 3 exam 2

  1. 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
  2. From 0mv to -80mv by opening K+ channels
    • a all channels closed
    • b K+ channels open Gk>0 vm negative
    • c equlibrium potential vm =Ek=-80 no net K+ current
    • d staring at vm=Ek=-80 gk>>gNa
    • e Na+channels open gNa>>gK vm more postive (rising phase) close to Ena
    • f Na+ channels close gK>>gNa (falling phase) k+ out
    • g resting membrane restored gK>>gNa
    • f
  3. Voltage gated sodium channels
    • -one long polypeptide
    • -fomer domains (I-IV)-form a pore
    • -each domain has six transmembrance helices (s1-s6)
  4. Voltage sensor
    s4 helic positively charged amino acids
  5. What happens when vm at -40mv or above ?
    • -voltage sensor moves
    • -chemical changes conformation
    • -pore opens up
  6. Selectivity filter
    • -partially hydrated Na+ions fit
    • -patially hydrated K+ ion are too large
  7. Patch clamp technique
    • -glass pipette forms a tight seal w/ membrane
    • -used to record the current through single ion channels
  8. 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
  9. steps of voltage gated sodium channels
    • 1 at -65 mv channel closed
    • 2 membrane voltage =-40mv channel opens
    • 3 inactivation by gloloular portaion of proton (ball)
    • 4 pore closes when voltage is -65mv ball is away
  10. Many different kinds of potassium channels
    • 1 leak channels open all the time
    • 2 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
  11. 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
  12. Action potential conduction down axon
    • positive charges spread causing membrane just ahead to depolarize and reach threshold
    • action potential only propagates in one direction b/c retractory
    • period-Na+ channels inactivated until membrane potential returns to rest
  13. myelin and nodes of ranvier
    • positive charges spread futher w/ myclin
    • voltage gated Na+ channels are only present in nodes of ranvier
  14. 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
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neuroscien part 3 exam 2