Lecture 3 and 5 Biophysics of the Neuronal Membrane pt 1 and 2 Flashcards

1
Q

briefly describe the structure/environment of neuronal membrane

A

lipid bilayer
transmembrane protein complexes form channels/pores with selective passing of ions
extracellular and intracellular fluid composed of water and ions dissolved

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2
Q

define ions

A

atoms/molecules that have lost or gained charge (electrons)

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3
Q

what’s a cation?

A

positive ion

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4
Q

what’s an anion?

A

negative ion

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5
Q

what unit is used to describe the concentration of solutes (ions) in a solution?

A

Mole

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6
Q

define a mole

A

a mole of substance is constituted by 6.022x10^23 of that substance

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7
Q

what is 1 Molar (M) solution?

A

1 mole of solute dissolved in 1 litre of solution

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8
Q

how will solutes travel in a concentration gradient with permeable membrane?

A

from an area of high to low concentration until there’s no difference in concentration

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9
Q

as well as concentration gradient, what other factor effects ion flow?

A

electrical charge

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10
Q

what is electrochemical equilibrium?

A

when the concentration gradient is opposite and equal to that of its electrical gradient

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11
Q

what does the Nernst equation calculate?

A

the equilibrium gradient of a given ion

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12
Q

what does the membrane potential (Vm) define?

A

the difference in potential between inside and outside the cell

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13
Q

write out the Nernst equation

A

Es = RT/ZF ln([s]out/[s]in)

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14
Q

define the terms of the nernst equation and their associated values

A

Es= equilibrium potential of ion (volts)
R= universal gas constant = 8.314 J/mol
T= temp = celsius + 273.15= K
Z- charge of ion e.g. +1 or -1
F= faraday’s constant- 96,485 C/mol

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15
Q

what does an Na+/K+ion pump do and why?

A

actively (using energy) pumps out 3 Na+ and in 2 K+, this overall pushes +1 out of neuron contributing to its negative potential
it maintains resting potential actively

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16
Q

what are the nernst/equilibrium potentials (Es) for K+ and Na+?

A

Ek ~ -80mV
ENa ~ +58mV

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17
Q

what 2 factors determine whether Na+ or K+ drive the neuronal membrane to their equilibrium potential?

A

permeability and concentration gradients

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18
Q

if Vm= Ek, what does this mean for the flow of K+?

A

there will be no net passive current of K+ ions- this would be the equilibrium potential of K+

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19
Q

what happens to the membrane with respect of K+ if Vm>Ek

A

the membrane has become depolarised
This will cause an efflux of K+ in order to restore Vm to Ek

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20
Q

What happens to the membrane with respect to K+ if Vm<Ek?

A

the membrane has become hyperpolarised
this will cause influx of K+ to restore Vm to Ek

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21
Q

define reversal potential

A

the Vm value which changes direction of net current of a particular ion

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22
Q

if Vm is not equal to Es, what 3 factors does the net current depend on?

A

Vm potential
Concentration gradient of ion
Membrane permeabillity for ion

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23
Q

which 2 ions mostly determine the permeability of resting membrane potential?

A

Na+ and K+

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24
Q

what are Na+ and K+ ‘trying’ to do do membrane potential?

A

push it to that of their equilibrium potential (-80mV for K+ an +58mV for Na+)

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25
Q

which ion has a higher permeability to the membrane and by how much

A

K+ has a higher permeability by around 100 fold

26
Q

Why is Vm at rest closer to Ek than ENa?

A

because the membrane has much greater permeability for K+ ions

27
Q

What does the Goldman-Hodgkin-Katz equation take into consideration which the Nernst equation doesn’t?

A

the ion permeability of more than one ion
(in addition to concentration gradient which Nernst does consider)

28
Q

write out the Goldman-Hodgkin-Katz equation

A

check book/slides (make sure the Cl- is the right way round

29
Q

what is the notation for ion conductance

30
Q

define gs?

A

the ability of a membrane to support current of a particular ion (S) through a particular ion channel

31
Q

what 2 factors determine conductance?

A

permeability and the concentration of ions available
(highest conductance= high permeability and high conc. of ions)

32
Q

write an equation to describe the relationship between conductance and resistance

A

g=1/R (they are inverse)

33
Q

what is driving force?

A

the difference in equilibrium potential and and membrane potential
(Es-Vm)

34
Q

write the equation for ohms law for ion species

A

Is= gs (Es-Vm)

35
Q

do outward currents of ions have negative or positive Is?

36
Q

do inward currents have negative or positive Is?

37
Q

describe the passive membrane potential as an electrical circuit

A

membrane potential (Vm) causes current (I) through conductance (dependant on resistance of ion channels g=1/r)
ion pumps- current source- batteries

38
Q

what determines the net flux of one ion?

A

its driving force and ionic conductance

39
Q

what measurement is net flux of ions in

40
Q

write a basic equation to calculate the net flux (current) of ions

A

Ix = gx x ∆voltage

41
Q

what is the total flux of ions across membrane?

A

sum of all individual ion currents

42
Q

write the equation for total flux of ions (current) across membrane

A

Itotal= INa+ Ik + ICl =
gNa (V-ENa) + gK (V-EK + gCl (V-ECl)

basically the total current is calculated from the sum of individual currents which itself is calculated from the conductance of each ion multiplied by the difference between membrane potential and equilibrium

43
Q

is permeability a constant or a function of something else?

A

a constant

44
Q

what are the relative permeabilities of the 3 major ion species?

A

PK= 1
PNa= 0.03
PCl = 0.1

45
Q

when V=0, what is the net flow of ions?

A

0 - this is resting potential

46
Q

How does a patch pipette attach?

A

it has a blunt tip with an opening, used to make a hole in membrane by suction, forming a vacuum with access to cytoplasm

47
Q

what are the 2 recording models of patch-clamps?

A

current clamp and voltage clamp

48
Q

describe a current clamp

A

constant current injected into neuron and voltage/response is measured

49
Q

describe a voltage clamp

A

instead of having a fixed current, there is a fixed voltage and any detected change in voltage is quickly corrected with current input

50
Q

what are the 2 types of voltage clamp?

A

two-electrode voltage clamp (TEVC)
single electrode voltage clamp (SEVC)

51
Q

what is the difference between TEVC and SEVC?

A

TEVC has 2 electrodes, one which records voltage and the other which passes current when the other electrode detects voltage change
SEVC has one electrode which both records voltage and injects current

52
Q

describe SEVC in vivo recordings in mouse primary visual cortex

A

voltage clamp used on mouse with short bursts of visual stimuli
during the stimulation series, there’s a significant change in the current being injected into the neuron, hence the visual stimulation is activating the neuron of the visual cortex

53
Q

to observe EPSCs, what is the ideal voltage clamp?

A

-70/-80 mV

54
Q

why is -70/-80 mV the ideal voltage clamp for EPSC observance

A

it is the reversal potential or inhibition (chloride)
it prevents spiking

55
Q

to observe IPSCs, what is the ideal voltage clamp?

56
Q

why is 0-20mV the ideal voltage clamp for IPSCs ?

A

it is reversal potential of excitation (potassium and sodium ions)
it prevents spiking

57
Q

what is put in the patch solution to prevent spiking/make the neuron more like an RC-circuit

A

sodium channel blockers- prevents spiking

58
Q

does visual stimulus invoke excitatory or/and inhibitory responses

59
Q

can excitatory and inhibitory responses be recorded at the same time?

A

no- because the voltage needs to be clamped at different levels depending on response to be oserved