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bioregulatory systems 🦠 > membrane potentials and action potentials > Flashcards

membrane potentials and action potentials Flashcards

1
Q

definition of Flux

A

the number of molecules that cross a unit area per unit of time (number of particles)

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2
Q

what are 2 properties of ions

A

they are charged molecules

opposites attract and like repel

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3
Q

3 electrical properties of excitable cells

A
  • voltage (potential difference) = generated by ions to produce a charge gradient
  • current = movement of ions due to a potential difference
  • resistance = barrier that prevents the movement of ions
    V = I x R
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4
Q

STEPS to measure membrane potential

A

1) place reference electrode outside of the cell = zero volt level
2) another electrode is placed inside the cell - measures a voltage that is negative compared with the outside (ie. reference)

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5
Q

properties of ion channels

A
  • lipid (hydrophobic) cell membrane barrier to ion movement and separates ionic environments
  • ion channels can open or close
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6
Q

what 3 things cause ion channels to open or close

A

1) transmembrane voltage
2) activating ligands
3) mechanical forces

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7
Q

when will movement across the membrane occur

A

when the concentration of the ion is different on one sided of the membrane and will stop when equilibrium is reached

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8
Q

when is the electrochemical equilibrium reached

A

when the conc gradient exactly balances the electrical gradient

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9
Q

what is 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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10
Q

what is the Nersnt equation (to calculate equilibrium potential)

A 
E = RT/zF ln X2/X1
X2 = intracellular ion conc
X1 = extracellular ion conc
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11
Q

what are the most important ions in determining resting potential of neurones

A

Na+ and K+

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12
Q

what is typical resting membrane potential

A

-70mV and each ions contribution to membrane potential is proportional to how permeable the membrane is to the ion at any time

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13
Q

GHK equation

A

Em (mV) = -61 log Pk[k]i + Pna[Na]i + Pcl[Cl]o/Pk[K]o + Pna[Na}o + Pcl[Cl}i

[x] represents conc and the subscript i or o indicates inside or outside the cell

P is permeability or channel open probability (0 = 100% closed, 1 = 100% open, 0.5 = open 50% of the time)

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14
Q

what is depolarisation

A

membrane potential becomes positive towards 0mV

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15
Q

what is repolarisation

A

membrane potential decreases towards resting potential (becomes more negative)

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16
Q

what is overshoot

A

membrane potential becomes more positive

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17
Q

what is hyperpolarisation

A

membrane potential decreases beyond resting potential

18
Q

what is a graded potential

A

change in membrane potential in response to external stimulation or NTs - and the change in membrane potential is graded in response to the type or strength of stimulation

19
Q

what do graded potentials do

A

produce the initial change in membrane potential that determines whether an action potential is initiated or prevented

20
Q

what happens to graded potentials over time

A

graded potentials decay along the axon as small amounts of charge leaks from the axon and so the size of that potential change decreases along its length

21
Q

what are ion channels opened by

A

membrane depolarisation

22
Q

what are ion channels inactivated by

A

sustained depolarisation

23
Q

what are ion channels closed by

A

hyperpolarisation/repolarisation

24
Q

what are the 5 phases of the action potential

A

phases 1-5

1) resting membrane potential
2) depolarising stimulus
3) upstroke
4) repolarisation
5) after-hyperpolarisation

25
Q

what is phase 1

A

resting membrane potential
permeability for Pk > Pna
membrane potential is nearer equilibrium potential for K+ (-90) than that for Na+ (+72)

26
Q

what is phase 2

A

depolarising stimulus

  • produces graded potential
  • the stimulus depolarises the membrane potential
  • moves in the positive direction towards threshold
27
Q

what is phase 3

A

upstroke
- starts at threshold potential
- increased permeability for Na because VGSCs open quickly
- increased permeability for K because VGKCs open slowly
K+ leaves the cell less than Na+ entering
membrane potential moves toward Na+ equilibrium potential

28
Q

what is phase 4

A

repolarisation

  • decreased permeability for Na as VGSCs close - entry stops
  • increased permeability for K as channels are still open so K leaves cell down EC gradient
  • membrane potential moves towards K+ Eq potential
29
Q

at the start of repolarisation…

A
  • absolute refractory period
    Na channel activation gate is open
    inactivation gate is closed
    new action potential cannot be triggered even with strong stimulus
30
Q

what happens at the peak of an AP

A

just after all Na+ channels are open they undergo a conformational change called inactivation

31
Q

what is inactivation and what does it do

A

impedes ion flow through Na+ channel > cannot be reopened

- only when cells repolarise completely - inactivation is removed from Na+ channel > closes and can be reopened

32
Q

what happens later in repolarisation

A
  • absolute refractory period continues
  • activation and inactivation gates closed
  • until repolarisation - inactivation is removed
  • cell channels are primed for reopening
    (during this time - cell cannot be stimulated)
33
Q

what happens in phase 5

A

after hyperpolarisation
- at rest, VGKCs still open
K+ continues to leave down EC gradient
- membrane potential moves closer to K+ equilibrium - some VGKCs close
- membrane potential returns to resting potential
- some Na+ channels open = relative refractory period (some Na+ channels have recovered from inactivation - gate is open)
stronger than normal stimulus is required to trigger AP

34
Q

what 2 things determine decay at the site of depolarisation

A
  • internal resistance of axon
  • membrane insulation
    alters propagation distance and velocity
35
Q

how does diameter affect decay

A
  • resistance of neurone is determined by diameter
    the larger the diameter = smaller resistance = slower decay
    smaller diameter = greater resistance = faster decay
36
Q

what does myelination do to decay

A

if there is insulation - graded potential decays further along axon due to insulation being provided

37
Q

what 2 factors affect conduction velocity

A

axon diameter

myelination

38
Q

how does axon diameter affect conduction velocity

A

as diameter increases = conduction velocity increases

conduction velocity is proportional to the square root of axon diameter

39
Q

how does myelination affect conduction velocity

A

as myelination increases so does conduction velocity

40
Q

what are 3 factors that influence movement of ions across a membrane

A

charge of ions
conc of ions on both sides
voltage across membrane

bioregulatory systems 🦠 (54 decks)

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