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4. BIOL257 > Resting membrane potential > Flashcards

Resting membrane potential Flashcards

1
Q

divide body fluid into 2 compartments:

A
  • intracellular fluid (ICF) = cytosol

- extracellular fluid (ECF)

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2
Q

extracellular fluid: general features

A
  • constant chemical environment vital for survival of cells (homeostasis)

consists of:

  • interstitial fluid (ISF)
  • plasma
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3
Q

extracellular fluid: define ISF

A

solution that bathes the non blood cells

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4
Q

extracellular fluid: define plasma

A

extracellular compartment of the blood

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5
Q

extracellular fluid: level of capillaries

A
  • interstitial fluid and plasma separated by single layer of endothelial cells intersperse w water filled pores
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6
Q

extracellular fluid: function of separation of interstitial fluid/ plasma

A

permits rapid change of all substances up to size of small protein btw plasma/ interstitial fluid

= plasma and ISF same conc. of solutes/ ions

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7
Q

difference in ICF and ECF: potassium

A
  • higher in ICF

- much lower in ECF

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8
Q

difference in ICF and ECF: sodium

A
  • lower in ICF

- much higher in ECF

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9
Q

difference in ICF and ECF: chloride

A
  • lower in ICF

- much higher in ECF

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10
Q

define amphipathic and eg:

A
  • having both -ve and +ve parts
  • phospholipid molecules polar phosphate head (hydrophilic)
  • non polar lipid tail (hydrophobic)
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11
Q

substances which can cross membrane via simple diffusion:

A
  • small non polar lipophilic

- v small uncharged polar molecules

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12
Q

substances which can’t cross membrane via simple diffusion:

A
  • larger uncharge polar molecules

- charged molecules and ions

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13
Q

substances which can’t cross membrane via simple diffusion: eg

A
  • amino acids
  • glucose
  • lactate
  • nucleotides
  • H+, K+, Na+, calcium, magnesium, chloride, bicarbonate (HCO3-)
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14
Q

substances which can cross membrane via simple diffusion:

A
  • O2, CO2, N2, fatty acids, steroid hormones

- H2O, urea, glycerol, ethanol

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15
Q

ion channels: features

A
  • pore forming integral proteins that span lipid bilayer
  • hydrophilic pore allows diffusion of charged ions across membrane DOWN electrochemical gradient
  • passive transport
  • no. and type of channels determines flow across membrane
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16
Q

list 5 types of ion channels:

A
  • selective
  • non gated
  • gated
  • fast
  • bidirectional
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17
Q

ion channels: selective

A

either:

  • allow only 1 ion species to pass (eg. Na+)
  • allow polarity of ion species (cation/ anion)
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18
Q

ion channels: non gated

A

aka leak channels: open/ close randomly

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19
Q

ion channels: gated and types

A

open and close based on specific stimuli:
- ligand gated (extra/intracellular chemical)

  • voltage (change in volt across membrane)
  • mechanically (mechanical deformation)
  • thermally (temp)
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20
Q

ion channels: fast

A

1x10(8) ions pass in 1 second

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21
Q

ion channels: bidirectional

A
  • net ion flux depends on electrochemical gradient
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22
Q

leak channels: features

A
  • selective but non gated channels
  • open/ close randomly
  • allow ions (K, Na, Cl) to diffuse passively across membrane DOWN electrochemical gradients
  • crucial for establishing resting membrane potential of cell
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23
Q

ion pumps and coupled carriers: features

A
  • integral proteins spanning lipid bilayer
  • move solutes (ions, glucose) against/ UP electrochemical gradient
  • active transport
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24
Q

ion pumps and coupled carriers: active transport requires metabolic energy by

A

directly:
- form of ATP

indirectly:
- form of chemical potential energy provided by another ion moving DOWN electrochemical gradient

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25
Q

ion pumps and coupled carriers: eg

A

sodium potassium pump

- primary active transport of K (inwards) and Na (outwards)

26
Q

impermeant anions:

A
  • many organic molecules are negatively charged (anions A-)
  • which are too big to be diffused through the bilayer
  • carry charge and also osmotically active
27
Q

name two biophysical principals for correct functioning of the body:

A
  • principal of equimolality

- principal of electrical neutrality

28
Q

principal of equimolality:

A

conc. of osmotically active particles inside cell (ICF) should be approx = to outside (ECF)

imbalance: water going into
- ICF -> ECF: cell shrinkage
- ECF -> ICF: cell swelling

29
Q

principal of electrical neutrality:

A 
total cation (+) conc. outside cell MUST = total anion (-) outside cell
- same for inside cell
30
Q

principal of electrical neutrality: plasma acidosis

A
  • high Cl/HCO3 or low Na = more H in plasma

- lowers pH

31
Q

principal of electrical neutrality: plasma alkalosis

A
  • low Cl/HCO3 or high Na = more OH in plasma

- raises pH

32
Q

impermeant anions: ICF balance

A

A- balanced by K = electrical neutrality

33
Q

impermeant anions: ECF balance

A

Cl- balanced by Na = electrical netrality

34
Q

impermeant anions: ECF and ICF balance

A

equimolality

35
Q

membrane potential=

A

Vm

36
Q

membrane potential: features

A
  • Vm measured relative to out of cell (ECF= 0)

- excitable cells capable of rapid change in response to stimulation

37
Q

resting membrane potential:

A

RMP

- cell at rest

38
Q

typical resting Vm: neurons

A

70 mV

39
Q

exceptions: K+

A
  • most common cation in ICF (balances A-)
  • accumulated from sodium/potassium pump
  • K will try to diffuse high to low (into ECF)
  • down its chemical concentration gradient
40
Q

chemical gradients:

A
  • chemical driving forces
  • ions move down chemical conc. gradient
  • from high to low
41
Q

charge separation:

A
  • some intracellular K+ diffuses out (via leak channels) leaving unmatched -ve charges (impermeant A-)
  • small difference in no. of charged ions btw inside/outside cell
  • charges will cluster near membrane
42
Q

charge separation: positive and negative charges found where?

A
  • slight +ve charges (outside)

- slight -ve charges (inside)

43
Q

electrical gradients: features

A
  • opposite charges attract
  • like charges repel
  • charge separation creates electrical driving force
44
Q

electrochemical gradient=

A

chemical gradient + electrical gradient

45
Q

electrochemical force=

A

net driving force combo of chemical and electrical driving force

46
Q

Na/K ATPase process:

A
  • K inwards, Na outwards
  • both move AGAINST electrochemical gradients
  • ATP -> ADP
  • 3 Na out of cell
  • 2 K into cell
47
Q

equilibrium occurs:

A

chemical and electrical driving forces are:
- opposite in direction, equal in magnitude

theoretical condition called ‘Equilibrium Potential E’

48
Q

importance of Equilibrium potential E:

A
  • tells which way ion will move across cell membrane at given membrane potential (Vm)
49
Q

Nernst equation for K:

A

61.3 ÷ (+1) or z times log [K]out ÷ [K]in

50
Q

forces on Na:

A
  • high [Na] outside -> low [Na] inside
  • chemical driving force pushes Na INTO cell
  • diffuses through leak channels
  • cell becomes less -ve, now exterior slight excess of -ve charges
  • membrane potential Vm occurs -> electrical driving force attracts Na back out
51
Q

E of K+

A

-95mV

52
Q

E of Na+

A

+66mV

53
Q

electrochemical force acting btw K and Na:

A
  • this force will move ion across membrane in direction bring Vm closer to E of ion
  • cells permeable to both ions
  • RMP (resting Vm) will fall btw EK and ENa
54
Q

typical neuron vs K:

A

neuron: -70mV vs EK= -95mV
EK < Vm
- chemical force drives K out > electrical force pulling K in
- net outward electrochemical force acting on K ions
- net outward flux/current of K ions

55
Q

typical neuron vs Na:

A
  • ENa = +66mV
  • Vm &laquo_space;ENa
  • both chemical and electrical force direct inwards
  • net inward electrochemical force acting on Na ions
  • net inward flux/current of Na ions
56
Q

define ion currents:

A
  • movement of ions across membrane

- ions carry electrical charges and mass across membrane

57
Q

magnitude of electrochemical force acting on particular ion is proportional to:

A

Vm - E

58
Q

membrane permeability:

A
  • also affects movement of ions

- most cells K is 25x more permeable than Na

59
Q

Goldman-Hodgkin-Katz (GHK) equation

A

used to see relationship btw RMP and both ion conc. and ion permeabilities (P) for cell

60
Q

maintaining RMP Vm:

A
  • without other mechanisms, chemical gradients would gradually dissipate due to diffusion = electrically neutral both sides (Vm=0)
  • cell actively transports K out and Na in using Na/K ATPase
61
Q

Na/K ATPase: features

A
  • uses ATP
  • in electrically active neurons (60-70%) of cell energy budget used to drive pump
  • removes 3 Na for every K brought in
  • electrogenic (net outward K current)
62
Q

Na/K ATPase: function

A
  • maintains steep Na gradient across cell for regulation of:
  • cytoplasmic pH
  • interacellular [Ca]
  • Na
  • cellular volume (osmotic balance)

4. BIOL257 (18 decks)

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