Action Potentials

Question 1

describe an action potential

Answer 1

• 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

Question 2

CA1 pyramidal neurons

Answer 2

hippocampus
glutamatergic principle cell
Afferents =
* CA3 pyramidal cells
* entorhinal cortex
* various hippocampal GABAergic neurons

Efferents =
* subiculum
* entorhinal cortez
* prefrontal cortex
* variosu GABAergic interneurons

Question 3

Orient-Lacunosum molecular interneurons

Answer 3

GABAergic interneurons
Afferents
*hippocampal pyramidal cells
*medial septum
* other interneurons

Efferents
*distal dendrites of CA1 pyramidal neuorns
*other interneurons

Question 4

how do differences in AP waveform come about

Answer 4

different threshold depending on properties of sodium channels

Question 5

does CA1 or O-LM have a more hyperpolairsed (lower) threshold

Answer 5

CA1 threshold is lower than O-LM

Question 6

explain the voltage gated sodium channel chain reaction

Answer 6

• 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

Question 7

when is the chain reaction triggered

Answer 7

Action potential threshold
absolute values varies depending on properties of sodium channel

Question 8

what are the alpha subunit subtypes of a CA1-PN

Answer 8

rNav1.6,1.2
2 types of cottage gates sodium channels

Question 9

what are the alpha subunit subtypes of interneurons (OLM)in CA1 in hippocampus

Answer 9

rNav1.1
one type of voltage gated sodium channel

Question 10

what do voltage gate sodium channels consist of

Answer 10

alpha subunit
(transmembrane domains and linkers)
beta subunit

Question 11

where does the difference between sodium ion channels lie

Answer 11

in the alpha subunit

Question 12

what is the V1/2

Answer 12

membrane potential when half sodium channels are open

Question 13

V1/2 for a NaV1.1 interneuron

Answer 13

-20mV

Question 14

V1/2 for a NaV1.2 pyramidal neuron

Answer 14

-24 mV

Question 15

V1/2 for a naV1.6 pyramidal neuron

Answer 15

-29 mV

Question 16

Why might one EPSP trigger an AP in the presynaptic cell and not the postsynaptic cell?

Answer 16

because the postsynaptic cell might have a higher (more depolarised) threshold.

Question 17

what control burst firing

Answer 17

afterpolarisation

Question 18

what is burst firing

Answer 18

the frequency of AP firing slows down with time

Question 19

what is burst firing

Answer 19

the frequency of AP firing slows down with time

Question 20

afterpolarisation

Answer 20

controls burst firing
after depolarising potentials are slower and smaller than AP

Question 21

how can afetrpolarisation trigger another AP

Answer 21

if the after depolarisation is sufficiently long or large = trigger another AP

Question 22

ionic mechanisms underlying large After hyper polarisation in GABAergic interneurons

Answer 22

• 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

Question 23

why does a larger AHP contribute to sustained high frequency firing

Answer 23

AHP controls a continuous high frequency firing

Question 24

voltage gated sodium channels in resting state

Answer 24

closed

Question 25

voltage gates sodium channels after depolarising stimulus

Answer 25

polarity of membrane changes gates are opened

Question 26

inactivation gate role

Answer 26

closes pore from the inside inactivated channel can't be activated if opened for a long time

Question 27

what does recovery from inactivation depend on

Answer 27

* 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

Question 28

when do channels move from inactive to closed state

Answer 28

depolarisation

Question 29

what is the recovery period

Answer 29

channels move from inactive to closed state

Question 30

what does re depolarising at a more positive (depolarised) level do to the second pulse

Answer 30

smaller current

Question 31

if APs in OLM cells are narrower ...

Answer 31

less inactivation sodium channels recover from inactivation faster promotes high frequency repetitive AP firing

Question 32

is APs in OLM cells have large AHP which pushes the membrane to more hyperpolarsed potentials

Answer 32

faster recovery from inactivation sodium channels recover from inactivation faster promotes high frequency repetitive AP firing