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BMS 752 (Medical Physiology) > Basic Electricity > Flashcards

Basic Electricity Flashcards

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USMLE® Step 1 flashcards
1
Q

coulombs law

A

the attraction between two ions increases or decreases based on charge and decreases the further apart two ions are

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2
Q

ohms law

A

the amount of number of ions that move from one area to another is equal to the voltage difference between the ions divide by the resistance

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3
Q

I = V/R

what is this? what are the variables?

A

Ohms law

I = Current

V = voltage difference

R = resistance

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4
Q

what is the physiologic definition of conductance

A

the rate at which an ion corsses a 1cm area of a membrane driven by a 1 M concentration gradient

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5
Q

what is the equation for conductance? what are the variables?

A

I = gV

I = current

g = conductance

V = voltage

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6
Q

what is the electrical definition of conductance

A

1 seimen of conductance will produce a 1 amp current when the potential is 1 volt

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7
Q

what formula is used to determine single species ion flow

A

Ix = gx (Vm - Ex)

I = current

g = conductance

(Vm - Ex) = the electrochemical driving force across a membrane

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8
Q

what happens to current when the membrane potential (Vm) is equal to the equilibrium potential (Ex)? why?

A

there is no flow of current

because there is no driving force

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9
Q

in Ix = gx (Vm - Ex), if Ix is negative, what does that mean? positive?

A

if current is negative that means that the equilbrium potential Ex is greater than the membrane potential Vm and postive ions will move into the cell

If current is positive then positive ions will move out of the cell

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10
Q

what is membrane potential?

A

the voltage created by differently charged ions on either side of a cell membrane?

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11
Q

what happens if a membrane potential is positive

A

cations are less likely to diffuse into the cell because the inside is positive

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12
Q

equilibrium potential

A

the membrane potential that will counteract the driving force behind a concentration gradient for a certain ion

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13
Q

what does it mean to say Na has and equilibrium potential of +60mV

A

it will require a membrane potental greater than 60mV to stop Na flux due to diffusion

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14
Q

what does it mean to say the equilibrium potential of potassium is -90mV

A

at any membrane potential greater than -90mV, K will flux into the cell due to the electrochemical driving force

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15
Q

what is the relationship between membrane potential and current

A

for Na and K, increasing the membrane potential will increase the current

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16
Q

define resting membrane potential

what is the RMP in a normal cell

A

the membrane potential created by a distribution of ions inside and outside the cell at rest

-70mV

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17
Q

at RMP, what is the driving force behind Na flux?

what is that called?

in what direction does it move?

negative or positive

A

the sum of the chemical energy from high Na concentrion outisde the cell and the electrochemical attraction to the anions in the cell

the electrochemical gradient

into the cell

negative

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18
Q

at RMP what is the driving force behind K flux?

what direction does it move?

negative or positive

A

the sum of the chemical energy difference move K out of the cell minus the electrostatic attraction of K to intracellular anions

out of the cell

positive

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19
Q

what is a normal ICF and ECF for sodium?

A

ECF 145mM

ICF 9.5mM

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20
Q

what is a normal ICF and ECF for potassium

A

ECF: 4.5 mM

ICF: 150mM

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21
Q

what is electrochemical gradient for sodium at rest

A

-3.29 kcal/mol

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22
Q

what is the electrochemical gradient for potassium at rest

A

0.27 kcal/mol

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23
Q

what are the three factors that influence RMP

A
  1. the attraction of extracellular cations to intracellular anions (Gibbs Donnnan)
  2. the membrane potential created by ion flux through leakage channels (net diffusion potential)
  3. the membrane potential created by ion pumps that create unequal distribution of ions (electrogenic pump potential)
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24
Q

gibbs donnan forces

A

the attraction between extracellular cations to intracellular bound anions

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25
Q

net diffusion potential

A

the membrane potential created by movement of ions through leak channels

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26
Q

if a membrane is only permeable to one ion, what will the net diffusion potential be?

A

the same as the equilibrium potential

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27
Q

what is the equilbrium potential for sodium

A

around 70mV

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28
Q

what is the equilbrium potential of potassium under normal conditions

A

-90mV

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29
Q

what is the net diffusion potential if the membrane is permable to more than one ion?

A

the average between the conductance of the ions

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30
Q

what is the equation for net diffusion potient? what does it mean

A

Ediff = (gK/(gk + gNa)EK + (gNa/(gk + gNa)ENa

the net diffusion potential for a cell is equal to the conductance K divided by the conductance of K and Na multiplied by the equilibrium potential for K, added to the conductance of Na over conductance of both ions times the membrane potential of Na

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31
Q

what two ions are not included in the chord conductance equation? why?

A

Cl and Ca

because Cl regulates passively and plays no role in forming potentials, and animal cell membranes are virtually impermeable to Ca

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32
Q

what can be used in place of conductance? why?

A

the number of leak channels available for a particular ion

because conductance is a measure of membrane permeabilty, and the only place a membrane is passively permeable to an ion is at a leak channel

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33
Q

what is the equation used to determine RMP? explain

A

Em = Ediff + EP

the RMP is equal to the net diffusion potential plus the electrogenic pump potential

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34
Q

what is the contribution of the following three factors or RMP

indirect Na/K

Gibbs donnan

electrogenic effect of Na/K

A
  • 56mV
  • 10mV
  • 4mV
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35
Q

what determines the status of a voltage gated ion channel

A

the membrane potential

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36
Q

how are voltage gated sodium channels responsible for rapid depolarization

A

they open and close quickly, allowing the amount of Na moving into the cell to change very fast

37
Q

what other ion is responsible for determining the voltage needed to open voltage gated ion channels? why

A

Calcium, because a significant amount of intracellular Ca will increase the membrane potential and decrease the electrochemical driving force of Na

38
Q

how fast do calcium channels open and close in comparison to Na channels?

why is this relevant

A

more slowly

calcium channels create a more sustained depolarization which is useful in cardiac and smooth muscle

39
Q

what are two types of calcium channels

A

L type and T type

40
Q

L type calcium channels

A

slower operating channels that create a sustained response

41
Q

T type calcium channels

A

transient type channels, create a more rapid response

42
Q

what are three functions of potassium channels

A
  1. Terminate action potentials
  2. modulate electrical excitability
  3. stabilize the resting potential
43
Q

what are three types of potassium channels

A
  1. delayed outward rectifiers
  2. transient outward rectifiers (A type)
  3. inward rectifiers
44
Q

what two potassium channels are in the Kv family?

what do they do

A

delayed outward and transient outward rectifiers

they allow potassium flux out of the cell to return the cell to RMP

45
Q

what are Kv1.1 and KV1.4

what is the difference between the two

A

outward rectifiers of the Kv family

Kv1.1 is slow to open and close, KV1.4 is fast

46
Q

what are inward potassium rectifiers

what do they do

A

potassium channels with a Mg “gate” that only allows one way diffusion of potassium

return the cell membrane back to RMP after hyperpolarization

47
Q

what is the process of a neuronal depolarization, propogation, and repolarization (10)

A
  1. Excitatory impulses release acetylcholine on to nicotinic receptors
  2. nicotinic receptors open ligand gated sodium channels
  3. summation of EPSPs opens enough ligand gated sodium channels to bring the neuron to threshold (-55mV)
  4. the axon hillock depolarizes, opening a cascade of Na channels
  5. the charge is propogated down the axon by sequentially opening Na channels
  6. As the membrane potential increases, voltage gated KV 1.4 channels open
  7. at Vm 30mV sodium channels are closed, KV 1.1 channels are open
  8. as Vm decreases, Kv 1.1 channels close slowly
  9. hyperpolarization occurs as Vm drops below RMP
  10. inward rectifiers allow potassium flux back into the cell to return it to RMP
48
Q

when is sodium conductance the highest in a neuronal cell? potassium?

A

during depolarization

during repolarization

49
Q

what is the RMP of skeletal muscle

A

-90mV

50
Q

what is the threshold potential for skeletal muscle

A

-70mV

51
Q

what current is responsible for depolarization of skeletal muscle? repolarizartion

A

INa

IKV1.1

52
Q

what are the five phases of a cardiac myocyte

A

Phase 4: rest

Phase 0: Upstroke

Phase 1: early repolarization

Phase 2: Plateau

Phase 3: final repolarization

53
Q

what is happening during Phase 4 of a cardiac myocyte contraction

A

maintenance of RMP caused by inward potassium rectifiers counteracting the flux of potassium out of the cell

54
Q

KIR

A

inwardly rectifying voltage gated potassium channels found on cardiac myocyte that keep the cell at RMP by balancing outward flux of potassium

55
Q

IKir

A

inwardly rectifying potassium current

56
Q

what current is responsible for Phase 0? what creates it

A

INA

flux of sodium through gated channels

57
Q

what is happening in Phase 1? what is the cause

A

early repolarization

transient outward rectifiying K channels open as Na gated channels are closing

58
Q

Ito

A

current created by potassium flux through transient outward gated potassium channels during phase 1 of a cardiac myocyte action potential

59
Q

A type rectifying channels

A

KV 1.4

60
Q

what is happening in phase 2? what is the cause?

A

plateau

potassium current outward through KV1.1 is balanced out by calcium current through L type caclium channels, resulting in a prolonged contraction

61
Q

what happens in cardiac pacemaker cells during phase 3? what is the cause?

A

final repolarization

L type calcium channels close, Kv1.1 channels are open, resulting in a strong outward IKv1.1

62
Q

what current is at work during each phase of a cardiac myocyte contraction and what direction is it moving

A

phase 4: IKir, into the cell

phase 0: INa, into the cell

phase 1: Ito

phase 2: ICaL, IKv1.4, IKv1.1

phase 3: IKv1.1

63
Q

what are the three phases of cardiac pacemaker depolarizaion

A

Phase 4: slow diastolic depolarization

Phase 0: Upstsroke

Phase 3: repolarization

64
Q

what is happening during phase 4 in a cardiac pacemaker cell? what causes it?

A

slow diastolic depolarization

If and ICaT currents bringing Na and Ca into the cell, IKv1.1 moving K out of the cell in opposition resulting in a slow progression to threshold

65
Q

why are Kv1.1 channels called delayed outward rectifiers

A

they are slow to completely open and slow to completely close

66
Q

what is happening during phase 0 in a pacemaker cell? what is the cause

A

upstroke

ICaL brining calcium into the cell through L type channels raises the Vm

67
Q

what is happening durin phase 3 in a cardiac pacemaker cell? what is the cause?

A

repolarization

IKv1.1 moving potassium out of the cell via delayed outward rectifiers

68
Q

what currents are in play during each phase of the cardiac pacemaker action potential

A

phase 4: If, ICaT, IKv1.1

phase 0: ICaL

phase 3: IKv1.1

69
Q

If

A

Funny current, a current found in phase 4 of pacemaker cells due to Na inward flux through non fast channels

70
Q

at what Vm do funny channels open

A

-50mV

71
Q

T/F smooth muscle doesn’t have Ca channels

A

false, they don;t have Na channels

72
Q

what ion channels cause depolarization in smooth muscle? why is this relevant

A

Calcium channels

because calcium channels open much slower than Na channels and produce a slower depolarization

73
Q

what is ion channels are responsible for repolarization of smooth muscle

A

Kv1.1

74
Q

what are the two refractory periods of an action potential

A

absolute and relative

75
Q

absolute refractory period

A

the interval during an AP at which time a second AP cannot occur in any circumstance

76
Q

what is the cause of the absolute refractory period

A

inactivation of Na channels until the cell is hyperpolarized

77
Q

relative refractory period

A

the interval when a second AP can occur but requires a stronger than normal stimulus

78
Q

what must happen during the relative refractory period to cause another AP

A

there must be a excitatory potential strong enough to open enough sodium channels to over come the slowly closing K channels

79
Q

what happens to charge when a membrane depolarizes

A

charge flows through the cytoplasm to other parts of the cell membrane

80
Q

cable properties

A

the ability of the cytoplasm to conduct electricity

81
Q

what two factors effect the cable properties of a cell

A
  1. rm
  2. rin
82
Q

rm

A

the resistance of the cell membrane to positive outward current

83
Q

rin

A

the viscocity of the cytoplasm

84
Q

what is the effect of rm on cable properties? rin?

A

increasing rm will increase cable properties

increasing rin will decrease cable properties

85
Q

length constant

A

the distance that a graded potential will travel through cytoplasm until it has diminished to 37% of its original strength

86
Q

where is depolarization the strongest? what happens as you move away from this point

A

at the point of membrane stimulation and it goes down the further away you go

87
Q

what two factors influence conduction velocity and how do they relate to the length constant

A
  1. diameter of the cell (viscosity)
  2. presence of myelin (membrane resistance)
88
Q

how does cell diameter influence viscosity

A

a smaller cell is more viscous, a larger cell is less viscous

89
Q

what is the equilbrium potential of sodium? potassium?

A

Na: 72.9 mV

K: -91.68 mV

BMS 752 (Medical Physiology) (13 decks)

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