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nuero > action/membrane potential > Flashcards

action/membrane potential Flashcards

1
Q

normal flow of ions

A

high to low concentration

until equilibrium is reached

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2
Q

why is it useful

A

transport over short distances
Spontaneous
No energy input required

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3
Q

what do ions produce as tehy flow from high to low

A

equilibrium value

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4
Q

what is flux

A

The number of molecules that cross a unit area per unit of time (number of particles).
i.e. molecules.m−2.s−1

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5
Q

what is voltage also known as

A

potential differnce

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6
Q

measured in

A

volts

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7
Q

how is P.D. generated

and what does it produce

A

Generated by ions to produce a charge gradient

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8
Q

what is current

A

Movement of ions due to a potential difference

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9
Q

measurement of current

A

Amps

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10
Q

what is resistance

A

Barrier that prevents the movement of ions

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11
Q

measurement of resistance

A

Ohms

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12
Q

when is the electrochemical equilibrium

A

achieved when electrical force prevents further diffusion across the membrane

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13
Q

what is the Equilibrium potential

A

the potential at which electrochemical equilibrium has been reached. It is the potential that prevents diffusion of the ion down its concentration gradient

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14
Q

what does the The Nernst Equation calculate

A

equilibrium potential (E

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15
Q

what is the equation

A

E=(RT/zF)-ln(x2/x1)

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16
Q

what do the letters stand for

A 
R = gas constant
T = Temperature in Kelvin
z = charge on ion (-1 for Cl-, +2 for Ca2+)
F = Faraday’s number - charge per mol of ion
ln = natural logarithm (log to base e)
X2 = intracellular ion concentration
X1 = extracellular ion concentration
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17
Q

what assumptions can be made

A

Assume T = 37 °C = 310 K

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18
Q

you must also convert natural log to what

A

common log

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19
Q

what is E measured in

A

mV

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20
Q

What accounts for the -20mV difference between the typical membrane potential and Ek

A

the membranes are permeable to other ions as well as the potassium like sodium which will make it more positive

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21
Q

each ion’s contribution to membrane potential is proportional what?

A

to how permeable the membrane is to the ion at any time

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22
Q

why does Goldman-Hodgkin-Katz (GHK) equation equation describes the membrane potential more accurate than The Nernst Equation?

A

the GHK takes into account permeability of the membrane to particular ions

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23
Q

what does a value of 1 for p describe

A

p is permeability or channel open probability

a value of 1 means the channel is open 100 percent of the time

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24
Q

what does a value of 0.5 for p show

A

the channel is open 50 percent of the time

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25
Q

what does Subscript on P indicate?

A

the ion

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26
Q

when the Electrochemical equilibrium is formed what 2 forces are balanced

A

electrical forces balance diffusional forces

27
Q

when will the nernst equation work

A

when the membrane is uniquely selective to one particular ion

28
Q

define Depolarisation

A

Membrane potential becomes more positive towards zero mV

29
Q

define Repolarisation

A

Membrane potential decreases towards resting potential

30
Q

Define Overshoot

A

Membrane potential becomes positive

31
Q

Define Hyperpolarisation

A

Membrane potential decreases beyond resting potential

32
Q

what causes a membrane potential to change

A

external stimulation or neurotransmitters

33
Q

what is the change in membrane potential graded by

A

the type or strength of stimulation

34
Q

what is the realtionship between distnace and potentail differnce

A

the p.d. will always decay from the site of the stimulus to father out

35
Q

what 2 changes in membrane potential can a stimulus cause

A

either depolarisation or hyperpolarisation

36
Q

why does the graded potential decay down the length of an axon

A

Charge ‘leaks’ from axon and the size of the potential change decreases along the axon

37
Q

an action potential can only occur when a graded potential reaches a…

A

threshold

38
Q

positives of nerve impulses

A

allow the transmission of information reliably and quickly over long distancesq

39
Q

a major function of nerve impulses

A

in cell-to-cell communication and can be used to activate intracellular processes

40
Q

what are changes in membrane potential is dependent on

A

opening or closing of ion channels

41
Q

are changes in membrane potential during the action potential are due to ion pumps?

A

no

due to flow of ions through an ion channel

42
Q

what are the 5 stages of action potential

A

Phase 1.
Resting membrane potential

Phase 2.
Depolarising stimulus

Phase 3.
Upstroke

Phase 4.
Repolarisation

Phase 5.
After-hyperpolarisation

43
Q

during phase 1, is the permiability of sodium higher than potassium

A

no

the permability of potassium is greater than sodium

44
Q

when does phase 3 start

A

at the threshold potential

45
Q

why does the permability of sodium increase?

A

because voltage-gated Na+ channels open quickly [Na+ enters the cell down electrochemical gradient]

46
Q

why doesn’t the membrane potential reach the sodium equilibrium potential

A

na channels close

47
Q

why does the permeability of the potassium increase

A

the voltage-gated K+ channels start to open slowly [K+ leaves the cell down electrochemical gradient]

48
Q

why does the entry of sodium stop in phase 4?

A

because the voltage-gated Na+ channels close

lower permeability for sodium

49
Q

why does the membrane potential go towards the potassium equilibrium potential

A

as more voltage-gated K+ channels open & remain open

K+ leaves the cell down its electrochemical gradient

50
Q

how is the na channel inactivated/closed

A

a portion of the sodium channel protien moves in to block the pore of the channel stopping sodium entering the cell

51
Q

what is the period of time when a new action potential cannot be triggered called

A

Absolute refractory period

52
Q

during that period, are the activation gates opened or closed

A

closed

53
Q

why is the refractory period important

A

it limits the amount of signalling

54
Q

are Na+ channels open during the relative refractory period

A

some gates are open

55
Q

why do you need a stronger stimulus to produce an action potential during the relative refractory period

A

due to hyperpolarisation, you need a larger depolarisation to reach the threshold

56
Q

what is the “all-or-none” principle

A

when a stimulus exceeds the threshold potential, the nerve will produce a complete response; otherwise, the response is graded and decays.

57
Q

the rate of graded potential/action potential decay along an axon is dictated by what factors

A

internal diamter
intenal resistance
how well it is insulated

58
Q

how does an axon being myelinated affect the time taken for the action potential to decay

A

takes longer

59
Q

what factors increase conduction velocity

A

higher axon diameter and more myelination

60
Q

what factors decrease the conduction velocity

A

with reduced axon diameter (i.e. re-growth after injury), reduced myelination (e.g. multiple sclerosis and diphtheria), cold, anoxia, compression and drugs (some anaesthetics)

61
Q

What are the three main factors that influence the movement of ions across the membrane?

A

Concentration of the ion on both sides of the membrane, the charge on the ion and the voltage across the membrane.

62
Q

Why is the K+ equilibrium potential negative (e.g. -70mV) and the Na+ equilibrium potential positive(e.g. +40mV) when both are positive ions?

A

More K+ inside the cell than outside so tend to flow out of the cell, while more Na+ outside the cell than in, therefore tend to flow into the cell. A potential of -70mV is needed to attract K+ and stop net outward flow, while a positive charge of +40mV is needed to repel Na+ from entering the cell.

63
Q

Which ion is important for the upstroke (rising phase) and which is important for the falling phase of the action potential?
In which direction do these ions move?

A

The upstroke mediated largely by Na+ ions moving down their concentration gradient into the cell. The falling portion of the action potential dominated by K+ ions moving down their concentration gradient and therefore exiting the cell

64
Q

What factors influence the speed of propagation of an action potential along an axon?

A

Larger diameter axons have lower resistance, so ions move faster – conduction velocity is proportional to the square root of the axon diameter.
There is a linear relationship between conduction velocity and myelin thickness

nuero (36 decks)

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