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Bsc Physiology (Year 1) > Membrane Potentials > Flashcards

Membrane Potentials Flashcards

1
Q

what is the assigned voltage for outside the membrane ?

A

0 mV

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2
Q

what is the value for the resting membrane potential ?

A
  • 70 mV

varies between -5 to -100 depending on the cell type

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3
Q

where is the membrane potential situated ?

A

within close proximity of the plasma membrane meaning that the rest of the intracellular/extracellular fluid remains a neutral charge

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4
Q

the magnitude of resting membrane potential depends on what 2 parameters ?

A
  1. the differences in specific ion concentrations

2. the differences in membrane permeability for the different ions

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5
Q

what are the 3 parts that make up the resting membrane potential ?

A
  1. sodium potassium pump
  2. voltage gated sodium ion channels
  3. potassium ion channels
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6
Q

explain the role that the ‘sodium potassium pump’ plays in the maintenance of resting potential (3 points)

A
  1. active transport (uses ATP)
  2. pumps 3 Na+ out
  3. pumps 2 K+ in
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7
Q

explain the role that the ‘voltage gated sodium ion channels’ play in the maintenance of resting potential (2 points)

A
  1. CLOSED (blocked by an inactivation gate)

2. membrane is impermeable to Na+

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8
Q

explain the role that the ‘potassium ion channels’ play in the maintenance of resting potential (3 points)

A
  1. OPEN
  2. K+ diffuses down electrochemical gradient
  3. doesn’t reach equilibrium due to electrical repulsion of more positive charge outside the membrane
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9
Q

state what it is meant by the key term - graded potentials

A

graded potentials are potential changes of variable amplitude and duration that are conducted decremental; it has no threshold or refractory period

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10
Q

explain how a ‘graded potential’ works (6 points)

A
  1. GP occurs + charge flows between origin + adjacent areas
  2. small region of PM becomes depolarised
  3. ion channels briefly open + become more negative than adjacent areas
  4. simultaneously, outside cell, positive regions flow to more negative regions
  5. depolarisation spreads to adjacent areas of PM
  6. local current moves P charges to depolarisation on outside and away from depolarised site on inside
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11
Q

depending on the initiating event, a graded potential can be what ?

A

depolarising or hyper polarising

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12
Q

can graded potentials be summated ?

A

yes

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13
Q

state what it is meant by the key term - action potentials

A

a brief all-or-nothing depolarisation of the membrane, which reverses polarity in neurones; it has a threshold and a refractory period and is conducted without decrement

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14
Q

charge varies from what in an AP ?

A

changes from - 70 to + 30 mV and then repolarizes age membrane

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15
Q

how do AP’s travel ?

A

action potential propagation over long distances (GP’s travel short distances)

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16
Q

state what it is meant by the key term - potential

A

the voltage difference between two points

17
Q

state what it is meant by the key term - membrane potential

A

the voltage difference between the inside and the outside of the membrane

18
Q

state what it is meant by the key term - equilibrium potential

A

the voltage difference across a membrane that produces a flux of a given ion species that is equal but opposite too the flux due to the concentration gradient of that specific ion species

19
Q

state what it is meant by the key term - resting potential

A

the steady transmembrane potential of a cell that is not producing an electrical signal

20
Q

state what it is meant by the key term - synaptic potential

A

a graded potential change produced in the post-synaptic knob in response to the release of a neurotransmitter by a pre-synaptic knob

21
Q

state an additional fact about ‘synaptic potentials’

A

may be depolarising (EPSP) or inhibitory (IPSP)

22
Q

state what it is meant by the key term - receptor potential

A

a graded potential produced at the peripheral endings of afferent neurones (or in separate receptor cells) in response to a stimulus

23
Q

state what it is meant by the key term - pacemaker potential

A

a spontaneously occurring graded potential change that occurs in certain specialised cells

24
Q

state what it is meant by the key term - threshold potential

A

the membrane potential at which an action potential is initiated

25
Q

state the 6 steps, in order, of the action potential mechanism

A
  1. resting potential
  2. generator potential
  3. threshold potential
  4. depolarisation
  5. repolarisation
  6. hyper-polarisation
26
Q

explain the following step of the action potential mechanism:

step 1 - resting potential (4 points)

A
  1. sodium potassium pump maintains resting potential
  2. active transport (used ATP)
  3. 3 Na+ out, 2 K+ in
  4. some K+ diffuses back out
27
Q

explain the following step of the action potential mechanism:

step 2 - generator potential (5 points)

A
  1. weak stimulus
  2. some Na+ channels open
  3. some Na+ diffuses in
  4. doesn’t reach AP threshold
  5. sodium potassium pump re-establishes resting potential
28
Q

explain the following step of the action potential mechanism:

step 3 - threshold potential (4 points)

A
  1. generator potential reaches AP threshold
  2. many voltage gated Na+ channels open (inactivation gate is removed)
  3. Na+ diffuses into the axon
  4. positive feedback mechanism
29
Q

explain the following step of the action potential mechanism:

step 4 - depolarisation (2 points)

A
  1. Na+ channels are open

2. Na+ diffuses into the axon

30
Q

explain the following step of the action potential mechanism:

step 5 - repolarisation (3 points)

A
  1. voltage gates K+ channels are open
  2. K+ diffuses out of the axon
  3. Na+ channels close
31
Q

explain the following step of the action potential mechanism:

step 6 - hyperpolarisation (2 points)

A
  1. K+ channels are slow to close

2. membrane potential becomes more negative (compared to resting potential)

32
Q

what are the two benefits of resting potentials ?

A
  1. ensures action potentials are discrete (don’t overlap)

2. ensures action potentials are unilateral

33
Q

what are the two types of refractory periods ?

A
  1. absolute refractory period

2. relative refractory period

34
Q

what are ‘absolute refractory periods’ ? (3 points)

A
  1. during the AP, a second AP can’t be generated, no-matter how strong the stimulus
  2. occurs when Na+ channels are open/opening
  3. the inactivation gate must be removed by repolarizing the membrane and closing the channels before they can re-open to a second stimulus
35
Q

what are ‘relative refractory periods’ ? (3 points)

A
  1. a second AP can be generated if stimulus is greater than usual
  2. some Na+ channels have returned to resting states, and some K+ channels are still open
  3. possible to depolarise the membrane again
36
Q

how much longer are relative refractory periods to absolute refractory periods ?

A

1 - 15 ms longer

Bsc Physiology (Year 1) (34 decks)

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