Action Potentials Flashcards
describe an action potential
- resting membrane potentials = maintained by lead K+ currents
- when membrane potential reaches threshold voltage gated sodium channels are activated
- more voltage gated sodium channels activated
- sodium channels inactivate and slower voltage gated potassium channels activated
- voltage gated potassium channels can cause an overshoot = after hyper polarisation (AHP)
- resting membrane potential re established
CA1 pyramidal neurons
hippocampus
glutamatergic principle cell
Afferents =
* CA3 pyramidal cells
* entorhinal cortex
* various hippocampal GABAergic neurons
Efferents =
* subiculum
* entorhinal cortez
* prefrontal cortex
* variosu GABAergic interneurons
Orient-Lacunosum molecular interneurons
GABAergic interneurons
Afferents
*hippocampal pyramidal cells
*medial septum
* other interneurons
Efferents
*distal dendrites of CA1 pyramidal neuorns
*other interneurons
how do differences in AP waveform come about
different threshold depending on properties of sodium channels
does CA1 or O-LM have a more hyperpolairsed (lower) threshold
CA1 threshold is lower than O-LM
explain the voltage gated sodium channel chain reaction
- positive sodium flow into cell
- results in a region of positive charge across the membrane
- local depolarisation activates nearby sodium channels causing more positively charge sodium ions to Flow into cell
when is the chain reaction triggered
Action potential threshold
absolute values varies depending on properties of sodium channel
what are the alpha subunit subtypes of a CA1-PN
rNav1.6,1.2
2 types of cottage gates sodium channels
what are the alpha subunit subtypes of interneurons (OLM)in CA1 in hippocampus
rNav1.1
one type of voltage gated sodium channel
what do voltage gate sodium channels consist of
alpha subunit
(transmembrane domains and linkers)
beta subunit
where does the difference between sodium ion channels lie
in the alpha subunit
what is the V1/2
membrane potential when half sodium channels are open
V1/2 for a NaV1.1 interneuron
-20mV
V1/2 for a NaV1.2 pyramidal neuron
-24 mV
V1/2 for a naV1.6 pyramidal neuron
-29 mV
Why might one EPSP trigger an AP in the presynaptic cell and not the postsynaptic cell?
because the postsynaptic cell might have a higher (more depolarised) threshold.
what control burst firing
afterpolarisation
what is burst firing
the frequency of AP firing slows down with time
what is burst firing
the frequency of AP firing slows down with time
afterpolarisation
controls burst firing
after depolarising potentials are slower and smaller than AP
how can afetrpolarisation trigger another AP
if the after depolarisation is sufficiently long or large = trigger another AP
ionic mechanisms underlying large After hyper polarisation in GABAergic interneurons
- both pyramidal neurons and interneurons express a range of different voltage gated potassium channels
- interneurons express high levels of Kv3 subtypes
- fast activating, fast deactivation channels are activates at very depolarised potentials
–> produce the large post-spike AHP
–> enable very fast repolarisation of the AP
–> maximises quick recovery of resting conditions of membrane
why does a larger AHP contribute to sustained high frequency firing
AHP controls a continuous high frequency firing
voltage gated sodium channels in resting state
closed
voltage gates sodium channels after depolarising stimulus
polarity of membrane changes
gates are opened
inactivation gate role
closes pore from the inside
inactivated channel
can’t be activated
if opened for a long time
what does recovery from inactivation depend on
- time = takes time for channels to move from inactivated to closed state
channel will open again proportionally to the amount of time passed since the first depolarising stimulus - voltage steps - depolarising at a more positive level it will show a smaller current on the second pulse
when do channels move from inactive to closed state
depolarisation
what is the recovery period
channels move from inactive to closed state
what does re depolarising at a more positive (depolarised) level do to the second pulse
smaller current
if APs in OLM cells are narrower …
less inactivation
sodium channels recover from inactivation faster
promotes high frequency repetitive AP firing
is APs in OLM cells have large AHP which pushes the membrane to more hyperpolarsed potentials
faster recovery from inactivation
sodium channels recover from inactivation faster
promotes high frequency repetitive AP firing
