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Membrane Excitability > Passive properties and excitability of the membrane > Flashcards

Passive properties and excitability of the membrane Flashcards

1
Q

what’s the equivalent circuit model?

A

representing ion channels impact in terms of electrical behaviour

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2
Q

what’s the symbol for battery/ion pump?

A

https://www.google.com/search?q=battery+circuit+symbol&safe=active&rlz=1C1CHBF_en-gbGB767GB767&sxsrf=ACYBGNTXpxpx5zSUsRdRIFpPI4V57wOWlA:1579437266082&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjB7sGp1o_nAhUYThUIHfqxBokQ_AUoAXoECA8QAw&biw=1280&bih=616#imgrc=rCiZiuvofV6iFM:

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3
Q

what does the ion channel/ battery generate?

A

voltage

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4
Q

what is voltage also known as?

A

electromotive force

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5
Q

what does the voltage determine?

A

current flow

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6
Q

for each set of ion channels, what does EMFion equal?

A

Eion for each set of ion channels

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7
Q

what is driving force?

A

difference between membrane and equilibrium potential

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8
Q

in the membrane what does conductance represent?

A

ion channel permeability

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9
Q

what is conductance?

A

how readily a current will pass through a material

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10
Q

how are conductance and resistance related?

A

inversely proportional (opposites)

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11
Q

what is resistance?

A

how much a material opposes the flow of current

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12
Q

what are the 2 assigned units for conductance?

A

Siemens (S) or Ohms-1 (Ω-1)

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13
Q

in the membrane is conductance constant or variable?

A

variable

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14
Q

what does conductance determine in membrane?

A

current at a particular membrane potential

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15
Q

what is ohms law?

A

the relationship between voltage and current

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16
Q

what equation represents the relationship between membrane potential, equilibrium potential, voltage and conductance?

A

(Vm- Eion)= Iion/ Gion

(membrane potential- equilibrium potential) = voltage/ conductance

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17
Q

if Vm=Eion is there current?

A

no

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18
Q

draw the symbol for capacitance

A

https://www.google.com/search?safe=active&rlz=1C1CHBF_en-gbGB767GB767&biw=1280&bih=616&tbm=isch&sxsrf=ACYBGNTnNiCP2mSg0C0qGFQny1V7D9n2Tw%3A1579437270517&sa=1&ei=1kwkXoWKH_zTgwep_oD4Ag&q=capacitance&oq=capacitance&gs_l=img.3…459116.460592..460868…0.0..0.0.0…….0….1..gws-wiz-img.vRUdKOzR7Zc&ved=0ahUKEwiFzdCr1o_nAhX86eAKHSk_AC8Q4dUDCAc&uact=5#imgrc=EPmf5l-w2v0LUM:

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19
Q

what do capacitors do?

A

store charge

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20
Q

what is a capacitor?

A

2 conductors separating by non-conductive material

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21
Q

what, biologically acts as a capacitor?

A

membrane

22
Q

what are the units of capacitance?

A

Farad (F)

23
Q

give the equation to calculate capacitance

A

Capacitance (C)= Stored charge (Q)/ Voltage (V)

24
Q

if there’s capacitance what happens as potential difference (voltage) increases, what happens to stored charge?

A

it also increases

25
Q

if there’s capacitance and potential difference reduces, what happens to stored charge?

A

it also reduces

26
Q

what occurs due to charge being moved on and off a capacitor?

A

capacitive current

27
Q

does capacitive currents affect IC conc/ ion gradients?

A

no- as long as the voltage change is <100 mV (+ or -)- as only a relatively small number of ions are required for capacitance

28
Q

what membrane factor determines total capacitance?

A

surface area of membrane

29
Q

if you simplify the equivalent circuit model, what 3 components are important?

A
  • conductance
  • equilibrium potential
  • capacitance
30
Q

how is total conductance calculated?

A

sum of all conductances

31
Q

how is total current calculated?

A

sum of all currents

32
Q

how is passive and active membrane behaviour recorded?

A

2 electrodes- one applies current to one part, another records current in another part

33
Q

if a negative current is applied, what happens to membrane?

A

hyperpolarisation

34
Q

if a positive current is applied, what happens to membrane?

A

depolarisation

35
Q

what’s different between current injected and current recorded?

A

current injected is seen as square

current recorded has lag

36
Q

if current was affected by conductance only, how would the current recorded look?

A

also a square

37
Q

what is causing the lag?

A

capacitance- must obey capacative law

38
Q

what is tau?

A

time constant

39
Q

what is time constant?

A

time taken to achieve a 63% change in voltage

40
Q

how is voltage calculated by rearranging capacitance equation?

A

V= Q/C

41
Q

how does increased capacitance affect rate of change?

A

reduces it

42
Q

how does decreased capacitance affect rate of change?

A

increases it

43
Q

how is Tau (t) calculated? (2 ways)

A 
t= C x R
time constant = capacitance x resistance 
or 
t= C/G 
time constant = capacitance/ conductance
44
Q

is capacitance usually constant or variable in a cell membrane and why?

A

constant as cell membrane SA doesn’t change

45
Q

if the duration of a stimulus is short, what must the intensity be to reach threshold?

A

high

46
Q

if the duration of a stimulus is long does the intensity need to be long to reach threshold?

A

no

47
Q

what are the 2 affects of conductance on membrane?

A

higher conductance , lower response
lower conductance, higher voltage

higher conductance, reduced Tau- reaches threshold quicker

48
Q

how is conductance related to neuromodulation?

A

inhibitory neurotransmitters increase conductance e.g. GABA

excitatory neurotransmitters reduce conductance e.g. glutamate

49
Q

is an elongated structure leaky?

A

yes

50
Q

the further away from source of current, how does current change?

A

gets lower- due to leakiness

Membrane Excitability (9 decks)

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