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Medicine Unit 2 > Electrochemical gradients > Flashcards

Electrochemical gradients Flashcards

1
Q

how do transporters and channels have fundamentally different properties

A

a cells phospholipid bilayer limits the passage of charged molecules across the cell membrane (lipid part of the cell membrane has high electrical resistance)
gap junctions, membrane transporters and ion channels provide routes for charged molecules to cross the cell membrane

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2
Q

what do ion channel characteristics contain

A

selectivity
gating

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3
Q

how can channels be gated

A

mechanically
ligand and/or voltage-gated

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4
Q

what do all cells have

A

a membrane potential

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5
Q

what does Ohm’s law define

A

the relationship among membrane potential (voltage)
current
conductance (inverse of resistance)
I=CV

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6
Q

live cells resting membrane potential

A

Vm or RMP
is negative with respect to the extracellular fluid

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7
Q

electrically excitable cells resting membrane potential

A

neurons and myocytes
-30 to -70 mV RMP
they have a larger number of K+ channels open at rest

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8
Q

primary function of Na+/K+ ATPase

A

establishment of the concentration gradients for Na+ and K+
needed to generate resting, graded and action potentials
only mildly electrogenic
nt result of the actions of Na+/K+ ATPase is Vm of -5 to -12mV

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9
Q

ion reversal potential

A

also known as the equilibrium potential
membrane potential where the net flow through any open channel is 0
Erev the chemical and electrical forces are in balance

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10
Q

what equation do you use to calculate the Erev

A

the Nerst equation
R= gas constant
T= temperature in K
z= ion charge
F=Fraday’s constant

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11
Q

sodium ion equilibrium potential

A

+60mV

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12
Q

potassium ion equilibrium potential

A

-88mV

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13
Q

in order to calculate RMP what must you account for

A

the relative contribution of each channel type
expressed in terms of permeability P
resting membrane potential will be close in value to the reverse potential for the ion that carries the majority of the resting current

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14
Q

what can easily pass through the phospholipid bilayer

A

gases
some neurotransmitters
small amphiphilic compounds (most general anaesthetics)

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15
Q

what does the bilayer have high resistance to

A

the passage of current

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16
Q

3 types of membrane proteins that enable charged molecules to cross the membrane

A

gap junctions
electrical synapses
membrane transporters

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17
Q

what are gap junctions

A

large pores that form between 2 adjacent cells and can pass ions and small molecules
includes ATP
electrical synapses are a specialised form of gap junctions

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18
Q

what are membrane transporters

A

also known as pumps
integral membrane proteins that mediate facilitated diffusion or active transport of ions and other small molecules across the membrane

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19
Q

facilitated diffusion

A

occurs via specific transport proteins, permeases
only allow specific ions/molecules to pass through the membrane

20
Q

three types of transporters

A

uniports
symports
antiports

21
Q

uniports

A

move a single molecule

22
Q

symports

A

move multiple molecules in the same direction

23
Q

antiports

A

move multiple molecules in opposing directions

24
Q

what do channels do

A

allow water or ions to flow rapidly through a water-filled pore

25
Q

channels information

A

direct connection between the intracellular and extracellular spaces
move small molecules
always move charged molecules down their concentration gradients, passive process
dissipate concentration gradients
extremely high speed 10x10^6 molecules per second

26
Q

pumps information

A

never any connection between the intracellular and extracellular spaces
can move larger molecules
using ATP, some pumps (anti ports) can move molecules against their concentration gradients, active
build up concentration gradients
slower 1 x 10^3 molecules per second

27
Q

typical membrane potential

A

+40mV to -70mV

28
Q

Vm

A

potential difference
relative measure
movement of one positive ion from the outside to the inside results in a +2 change in Vm

29
Q

depolarisation

A

movement to a more positive membrane potential

30
Q

hyperpolarisation

A

movement to a more negative membrane potential

31
Q

principle intracellular cation

A

potassium

32
Q

principle extracellular cation

A

sodium

33
Q

principle anion

A

chloride
mainly extracellular

34
Q

environment outside the cell compared to inside

A

inside is more negative than outside
more negative ions inside the cell
resting membrane potential as there is no active stimulus

35
Q

how do you measure membrane potential

A

micro electrode

36
Q

mammalian neuron at 37 degrees Nerst equation

A

K+ is -90
Na is +61
Cl- is -52

37
Q

what is used to maintain the resting potential

A

sodium-potassium pump

38
Q

action potential

A

generated in the presence of a stimulus
nerve endings are stimulated
sodium channels open
membrane is depolarised
membrane potential changes from -70 to +40
reaches the threshold potential
all sodium channels open
more sodium ions move into the cell

39
Q

threshold/ all or nothing principle

A

when the membrane potential reaches +40mV the threshold is reached and all the sodium ion channels will open to allow influx of sodium ions into the cell

40
Q

repolarisation

A

once the membrane is depolarised
sodium channels will close and the potassium channels will open
membrane is repolarised as the membrane potential becomes more negative
may fall into a temporary overshoot known as hyper polarisation
new action potential can’t be generated, known as the refractory period
sodium potassium pump maintains the potential

41
Q

what occurs if there is an electrolyte imbalance

A

the equilibrium potential and membrane potential will change

42
Q

hypokalaemia

A

more potassium ions leak out of the cell during the resting state
changes the membrane potential to a more negative value of -90

43
Q

hyperkalaemia

A

fewer potassium ions move out of the cell through leaky potassium channels
resting potential becomes less negative
elevated plasma (extracellular fluid) K+ concentration

44
Q

effect of current on membrane potential

A

direction of current alters the membrane potential
efflux of positive ions cell will become hyper polarised
influx of positive ions the cell may become depolarised and generate an action potential

45
Q

what can cause a change in potassium ion concentrations

A

increased intake
decreased renal elimination
renal failure
adrenal disease
medications that alter kidney function
angiotensin-converting enzyme inhibitors
angiotensin II receptor blockers
potassium-sparing diuretics
non-steroidal anti-inflammatory drugs
increased release from intracellular stores due to tissue damage

46
Q

effects of high potassium on the body

A

irregular heartbeat
changes in mood
chest pain
shortness of breath
weakening pulse
heart palpitations
kidney conditions
nausea, vomiting or diarrhoea
numbness or tingling
muscle weakness

47
Q

most life threatening consequence of hyperkalemia

A

arrhythmia
cardiac arrest
due to depolarisation of the resting potential of cardia myocytes

Medicine Unit 2 (28 decks)

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