4. BIOL257 > Resting membrane potential > Flashcards

Resting membrane potential Flashcards

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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
ion pumps and coupled carriers: eg
sodium potassium pump | - primary active transport of K (inwards) and Na (outwards)
26
impermeant anions:
- 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
name two biophysical principals for correct functioning of the body:
- principal of equimolality | - principal of electrical neutrality
28
principal of equimolality:
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
principal of electrical neutrality:
``` total cation (+) conc. outside cell MUST = total anion (-) outside cell - same for inside cell ```
30
principal of electrical neutrality: plasma acidosis
- high Cl/HCO3 or low Na = more H in plasma | - lowers pH
31
principal of electrical neutrality: plasma alkalosis
- low Cl/HCO3 or high Na = more OH in plasma | - raises pH
32
impermeant anions: ICF balance
A- balanced by K = electrical neutrality
33
impermeant anions: ECF balance
Cl- balanced by Na = electrical netrality
34
impermeant anions: ECF and ICF balance
equimolality
35
membrane potential=
Vm
36
membrane potential: features
- Vm measured relative to out of cell (ECF= 0) | - excitable cells capable of rapid change in response to stimulation
37
resting membrane potential:
RMP | - cell at rest
38
typical resting Vm: neurons
70 mV
39
exceptions: K+
- 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
chemical gradients:
- chemical driving forces - ions move down chemical conc. gradient - from high to low
41
charge separation:
- 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
charge separation: positive and negative charges found where?
- slight +ve charges (outside) | - slight -ve charges (inside)
43
electrical gradients: features
- opposite charges attract - like charges repel - charge separation creates electrical driving force
44
electrochemical gradient=
chemical gradient + electrical gradient
45
electrochemical force=
net driving force combo of chemical and electrical driving force
46
Na/K ATPase process:
- K inwards, Na outwards - both move AGAINST electrochemical gradients - ATP -> ADP - 3 Na out of cell - 2 K into cell
47
equilibrium occurs:
chemical and electrical driving forces are: - opposite in direction, equal in magnitude theoretical condition called 'Equilibrium Potential E'
48
importance of Equilibrium potential E:
- tells which way ion will move across cell membrane at given membrane potential (Vm)
49
Nernst equation for K:
61.3 ÷ (+1) or z times log [K]out ÷ [K]in
50
forces on Na:
- 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
E of K+
-95mV
52
E of Na+
+66mV
53
electrochemical force acting btw K and Na:
- 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
typical neuron vs K:
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
typical neuron vs Na:
- ENa = +66mV - Vm << ENa - both chemical and electrical force direct inwards - net inward electrochemical force acting on Na ions - net inward flux/current of Na ions
56
define ion currents:
- movement of ions across membrane | - ions carry electrical charges and mass across membrane
57
magnitude of electrochemical force acting on particular ion is proportional to:
Vm - E
58
membrane permeability:
- also affects movement of ions | - most cells K is 25x more permeable than Na
59
Goldman-Hodgkin-Katz (GHK) equation
used to see relationship btw RMP and both ion conc. and ion permeabilities (P) for cell
60
maintaining RMP Vm:
- 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
Na/K ATPase: features
- 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
Na/K ATPase: function
- maintains steep Na gradient across cell for regulation of: - cytoplasmic pH - interacellular [Ca] - Na - cellular volume (osmotic balance)
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