Action Potentials Flashcards
describe what happens in an action potential
stimulus
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initial depolarization
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Depolarization
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Rising phase
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peak
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overshoot
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repolarization
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falling phase
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resting potential
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hyperpolarization
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return to resting potential
What are the main characteristics in an AP
- exhibits a threshold voltage (all or nothing)
- displays a rapid change in Rm
- has Sequential opening and closing of voltage-gated channels (depolarization, repolarization)
- once generated, is actively propagated (unchanged & in one direction) along axonal membrane
- is a discrete signal; transient with quick return to RMP
which types of channels are used for:
RMP
GP
AP
RMP - K+ leak channels
GP- no channels (electrotonic)
AP - voltage-regulated Na+ and K+ channels
at Vthresh some voltage gated Na+channels open & some Na+….
some Na+ moves in along its concentration gradient
this starts the hodgkin and Huxley cycle
where is the highest concentration of NaV channels found
in the hillock
also the hillock has lowest V thresh
the hodgkin cycle is an example of …
positive feedback loop
- initial depolarization
- opening of voltage-gated Na+ channels increases Pna
- increased Na+ flow
- further membrane depolarization
does it matter how much stimulus is given after reaching threashold?
No, as soon as threshold is reached the amount of voltage does not matter, the same height of AP will be reached either way.
what is a bursting neuron?
when longer depolarizing current causes bursting neurons (AP)
closing of NaV channels is also voltage-_____
does it occur fast or slow?
voltage-regulated
- thru an inactivation gate but structure is not well-known
- occurs slowly, causing an overshoot
- eventually all Na+ channels close by ~+40 mV
repolarization is due to _____
voltage-activated K+ channels
- these channels open/close more slowly than the NaV
- allows excess K+ to leave the cell
absolute refractory period
the period of time where a second AP cannot be generated since it is in a depolarizing or repolarizing phase
relative refractory period
the interval of time during which a second AP can be initiated, but initiation will require a greater stimulus (GP) than before
is Rm is very low, what is tau
tau would be very short, this allows rapid changes in Vm
larger diameter axons have a ____ V thresh
larger diameter axons have a lower Vthresh
AP is propagated _____ along entire axon and in ___ direction only
AP is propagated unchanged along entire axon and in one direction only
