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MEDICINE YEAR 1 > membrane and action potentials > Flashcards

membrane and action potentials Flashcards

1
Q

what is the resting membrane potential in a typical nerve cell

A

-70 mV

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2
Q

what is the sodium equilibrium potential

A

+60 mV

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3
Q

what is the potassium equilibrium potential

A

-90 mV

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4
Q

what is equilibrium potential

A

when the conc. gradient and electrical gradient balance out each other (equilibrium)and no net movement of ion occurs, the potential that would exist at this equilibrium is known as the equilibrium potential

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5
Q

what is the relative membrane permeabilities of sodium and potassium ions

A

Na+: 100
K+:1

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6
Q

what is the value for the sodium, potassium and chloride ion concentrations inside and outside the cell

A

inside and outside:
Na+ : 15 mM,150mM
K+ :150 mM, 5 mM
Cl- : 7 mM,110 mM

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7
Q

what is the Nernst equation for calculating equilibrium potential

A

Eion= 61 log 10 [ion]o/[ion]i

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8
Q

state the Goldman-Hodgkin-Katz equation to calculate membrane potential

A

Em= 61 log Pk [K+]o+ PNa [Na+]o/Pk [K+]i + PNa [Na+]i

log base 10, Pk=1 PNa=0.01

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9
Q

why are the resting membrane potential and potassium equilibrium potential not identical?

A

Due to the slight inward leak of Na+ into the cell (down the Na+-electrochemical gradient)

increases membrane potential from Ek

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10
Q

The plasma membranes of all cells are polarised electrically
true or false

A

true

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11
Q

The plasma membranes of all cells are electrically neutral

  true or false
A

false

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12
Q

concentration gradient for Na+ is outward/inward

A

inward

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13
Q

concentration gradient for K+ is outward/inward

A

outward

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14
Q

At resting potential the membrane is ___ times more permeable to K+ than Na+.

A

100

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15
Q

At resting potential the membrane is 100x more permeable to __ than __

A

K+, Na+

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16
Q

The 2 opposing forces acting on K+:
______ gradient -tending to move K+ out of the cell
_______ gradient -tending to move K+ into the cell)

A

concentration, electrical

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17
Q

the Na+-K+ pump generates a hyperpolarizing current

true or false

A

true

3 +ve go out for 2 in, net 1+ve goes out- leaves -ve overall charge in

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18
Q

what is depolarization

A

the inside of cell becomes less negative ( more +ve)

19
Q

what is hyperpolarization

A

the inside of the cell becomes more negative

20
Q

Na+ selective ion channel effects the membrane potential by

A

Depolarization

Inward current: Vm is driven toward ENa+:becomes more +ve

21
Q

K+ selective ion channel effects the membrane potential by

A

Hyperpolarization

Outward current:Vm is driven to EK+: becomes more -ve

22
Q

what is neuronal action potential

A

they are electrical signals which momentarily reverse the polarity of the nerve cell membrane

23
Q

what is threshold

A

To generate an action potential, the cell needs to reach threshold

about -55 mV, they are all or none

24
Q

what is upstroke and downstroke

A

upstroke: rise during depolarization till 0 mV
downstroke: fall from 0 mV during hyperpolarization

25
Q

what is overshoot and undershoot

A

overshoot: peak of action potential from 0 mV
undershoot: fall of action potential from resting potential

26
Q

Na+ ion channel in its closed stage is

A

non- conducting

inactivation gate is open, activation gate is closed

27
Q

Na+ ion channel in its open stage is

A

conducting

28
Q

Na+ ion channel in its inactivated stage is

A

non-conducting

inactivation gate is closed, activation gate is open

this allows for a refractory period

29
Q

what is an absolute refractory period?

A

no stimulus can elicit a secondary action potential

all Na+ channels are inactivated and membrane is depolarized and repolarized

30
Q

what is a relative refractory period?

A

a stronger than normal stimulus may elicit a secondary action potential

some Na+ channels are closed not inactivated now, and membrane is hyperpolarized

31
Q

how does an impulse propagate in a myelinated nerve fibre?

A

saltatory conduction

it “jumps” from each node- nodes of raniver–> occurs due to local current flow

32
Q

how does an impulse propagate in a un-myelinated nerve fibre?

A

contiguous conduction or passive conduction

33
Q

List the 3 types of gated ion channels

A

.membrane voltage: voltage-gated ion channels (VGICs)

.chemical substances:ligand-gated ion channels (LGICs)

.physical stimuli e.g., mechanical, thermal

34
Q

The ion channels responsible for the action potential in neurones are ____ gated ion channels

A

voltage

35
Q

Driving force for Na+ influx

A

-130 mV

Vm- ENa+= -70-60=-130 mV

since its negative causes inward movement

36
Q

Driving force for K+ efflux

A

+20 mV

Vm-EK+= -70-(-90)= 20 mV

since it’s +ve causes outward movement

37
Q

what causes upstroke in action potential

A

upstroke (depolarizing phase) is mediated by the opening of voltage-activated Na+ channels

38
Q

what causes downstroke in action potential

A

downstroke is due to the opening of voltage-activated K+ channels and the inactivation of voltage-activated Na+ channels

39
Q

what causes undershoot in action potential

A

undershoot is due to delayed closure of voltage-activated K+ channels

40
Q

ways to increase passive conduction

A
  • increase diameter of axon
  • decrease leak of current by insulating material- myelin–> schwann cells in PNS and ogliodendrocytes in CNS

schwann cells and ogliodendrocytres are both types of macroglia

41
Q

how does the activation of Na+ ion channels work?

A

The activation of Na+ channels is self-reinforcing – the opening of a few channels causes further channels to open, causes further depolarization

positive feedback

42
Q

what causes activation of Na+ ion channels ?

A

depolarization.

43
Q

how does activation of K+ ion channels work?

A

The activation of K+ channels is self-limiting – outward movement of K+ causes repolarization which turns off the stimulus for opening This is negative feedback

44
Q

what causes activation of K+ ion channels?

A

depolarization

MEDICINE YEAR 1 (6 decks)

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