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SMP - MCP Exam 2 > Lecture 18: Intro to Neurophysiology & Membrane Potentials > Flashcards

Lecture 18: Intro to Neurophysiology & Membrane Potentials Flashcards

1
Q

What is Fick’s Law’s equation?

A

Ji = Di.A . (C1-C2)/ x

  • Ji = flux/mvt of substance i between 2 compartments via simple diffusion
  • Di = diffusion coeff for the specific ion (which includes the partition coefficient)
  • A = area over which diffusion takes place
  • x = distance = membrane thickness
  • C1-C2) = concentration gradient
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2
Q

What is Fick’s Law’s equation for the diffusion of an ion between the exterior and interior of the cell?

A

Jx = Px . (X0-Xi)

Px = permeability coeff

X0 = concentration outside the cell

Xi = concentration inside the cell

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3
Q

What is the permeability coefficient Px specific to? What is it affected by?

A
  • Specific for a given molecule/ion
  • Affected by # and type of channels that the ion can pass through
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4
Q

What does the permeability coefficient Px combine?

A
  1. Lipid/water partition coefficient (whether the ion prefers to be in lipids or water)
  2. Diffusion coefficient
  3. Membrane thickness
  4. Standard 1 micron squared area
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5
Q

What are gated channels?

A

Channels that can be open/closed by chemical, voltage, light, or mechanical forces

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6
Q

What are 3 names that non-gated channels are referred to as? What are they specific too? Can these be open/closed?

A
  1. Pores
  2. Passive channels
  3. Leaky channels

⇒Specific to ions

NOPE, they are always OPEN!

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7
Q

How does an increase in temperature affect the diffusion coefficient and the permeability?

A

It increases both

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8
Q

What are the 2 resting properties of the cell?

A
  1. Membrane resistance
  2. RMP
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9
Q

What channels are important in determining the resting properties of the cell?

A

Leaky channels

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10
Q

What is Jmax?

A

The max movement of ions due to the limited number of channels (traffic jam)

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11
Q

Can Jmax be attained physiologically?

A

NOPE

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12
Q

What is the electrical equivalent of ion channels?

A

Battery in series with variable resistor

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13
Q

What is the equation for Ohm’s Law?

A

V = R.I

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14
Q

What is the equation for conductance?

A

G = 1/R

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15
Q

What is the equation for current?

A

I = G.V

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16
Q

What electrical properties do all channels control?

A

Resistance and conductance

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17
Q

What electrical property does permeability refer to? What is the slight difference between the 2?

A

Conductance

Difference: permeability is the ABILITY of an ion to move across a membrane and is dependent on the # of channels VS conductance is an actual electrical measurement of the movement of ions (flux)

⇒ you cannot have conductance without flux of ions = current

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18
Q

What is conductance dependent on in an ion channel?

A

The amount of current that can flow through: intrinsic property of the channel

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19
Q

What is the unit of resistance?

A

Megaohms

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20
Q

What is the unit of conductance?

A

Picosiemens or nanosiemens

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21
Q

What is the unit of voltage?

A

mV

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22
Q

What is the unit of current?

A

Nanoamperes or picoamperes

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23
Q

How many subunits does a typical voltage-gated channel have?

A

4

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24
Q

What are Na+ voltage-gated channels similar to?

A

Ca2+ voltage-gated channels

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25
Q

What part of the voltage-gated channel acts as the selectivity filter? How does this work? Where is it located?

A

P-loop: negatively charged to let positively charged ions through

Strategically placed at the interface between different subunits of the channels

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26
Q

What is the electrochemical equilibrium?

A

The equilibrium reached when electrical forces and concentration differentials stabilize and the movement of ions in = movement of ions out

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27
Q

What causes a voltage across a membrane?

A

A charge differential

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28
Q

What equation determines when the electrochemical equilibrium is reached? What does it provide? Write it out.

A

The Nernst equation: provides the voltage at which an ion is in electrochemical equilibrium given initial concentrations.

EK = 60/z . log ([Kout]/[Kin])

  • EK = equilibrium voltage of K+
  • z = charge of the ion
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29
Q

Describe the RMP in terms of inward current of Na+ and outward current of K+?

A
  • IK+INa = 0
  • IK = - INa
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30
Q

What equation to use to determine the resting membrane potential? Write it out.

A

The Goldman-Hodgkin-Katz equation

  • P: permeability of that ion
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31
Q

What is the difference between electrochemical equilibrium and RMP?

A
  • Electrochemical equil: does not require energy to reach and happens naturally
  • RMP: steady state so requires energy (ATP) used by the N+/K+ ATPase
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32
Q

What equation to use to calculate the current of a specific ion through a membrane? Write it out.

A

Modified version of Ohm’s Law:

I = G . (Vm<span> </span>- Eeq)

  • I = current of an ion
  • G = conductance
  • (Vm<span> </span>- Eeq) = driving force of ion movement = RPM - equilibrium voltage for a given ion
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33
Q

What happens if Vm = Eeq ?

A

No current for that ion ⇒ membrane potential is at the reverse potential for that ion

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34
Q

What equation to use to calculate RMP AT STEADY STATE when you have the conductances and know the equilibrium constants for each ion?

A

Conductance equation:

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35
Q

In the electrical circuit analog, what is the driving force for movement of an ion across a membrane?

A

The difference between the membrane potential and the equilibrium potential for that ion

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36
Q

What are scaffolding proteins?

A

Proteins that create a frame to help anchor specific proteins to the lipid bilayer

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37
Q

What enables a cell to create an action potential?

A

It’s able to separate its intracellular composition from the extracellular composition

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38
Q

Where is Cl- concentration higher: inside or outside the cell?

A

OUTSIDE

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39
Q

What is the effect of channels on the permeability of the membrane?

A

Increase permeability coefficient

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40
Q

What is the rate at which Na+, K+, and Cl- can cross the membrane?

A

106 ions/sec

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41
Q

What are ligand-gated channels?

A

Channels that need a ligand to bind to be activated

42
Q

What are water channels?

A

Aquaporins: control osmotic movement of water

43
Q
A
44
Q

What controls the selectivity filter of the voltage-gated channels?

A

Voltage sensor that senses changes in voltage to activate the voltage-gated channel

45
Q

Is it possible to have an inactivated voltage-gated channel when there is a voltage being experienced?

A

Yes

46
Q

Describe the composition of the voltage-gated channels.

A

Water-filled pore and group of AAs that loosely bind the ion

47
Q

How

A
48
Q

How many subunits does a ligand-gated channel have?

A

5

49
Q

How many subunits does a gap junction have?

A

6

50
Q

What is the fifth red segment on a hydropathy plot?

A

The pore domain: where ion permeation takes place

51
Q

What is the permeability ratio?

A

The ratio of channels

52
Q

What is the permeability ratio of the K+/Na+ channels in a neuron cell?

A

100:1

53
Q

What is the equilibrium potential of K+?

A

-58mV

54
Q

What is the equilibrium potential of Na+?

A

+60mV

55
Q
A

-58mV

56
Q

What do to with the Goldman-Hogkin-Katz equation when one of the ions cannot pass through the membrane?

A

Take it out of the equation!

57
Q

What does it mean for a pump to be electrogenic?

A

It hydrolyze ATP to transport ions across biological membranes leading to the translocation of net charge across the membrane (eg: 3 Na+ for 2 K+)

58
Q

What is considered positive current?

A

Current going out of the cell = positive outward current

59
Q

What is considered negative current?

A

Current going into the cell = inward negative current

60
Q

What kind of current makes the cell depolarize?

A

Negative inward current

61
Q

What kind of current makes the cell hyperpolarize?

A

Positive outward current

62
Q

What is capacitance? How do you calculate it?

A

Ability to store charge

C = Q/∆V

  • Q = charge (in Coulomb)
  • ∆V = change in voltage
63
Q

What is the unit of capacitance?

A

Farad

64
Q

How to vary the capacitance of a capacitor?

A

Increasing the distance between the plates of the capacitor: decrease capacitance

65
Q

How does permeability relate to membrane resistance? Conductance?

A

High permeability = low membrane resistance = high conductance

66
Q

What kind of ion movement through membrane channels? What is the exception?

A

Facilitated diffusion with transport maximum

Resemble simple diffusion except at Jmax

67
Q

Describe the structure of ion channels.

A

Mutiple subunits with distinct transmembrane segments.

68
Q

What type of channels does a glial cell have?

A

K+ channels only

69
Q

What does the RPM refer to?

A

The electrical potential of the inside of the cell

70
Q

Can an ion that is not permeable to a membrane affect the membrane’s RMP?

A

Not technically, but calcium is special in that way

71
Q

How can one measure the permeability, G, of an ion?

A

Slightly increase or decrease the concentration and see if the membrane potential changes because V=G.E (E depends on concentration):

  • If it does: ion is permeable
  • If it does not: ion is not permeable
72
Q

How does the flux of K+ relate to the flux of Na+ at steady state?

A

INa+ = - IK+

73
Q

If the ion channels were included on an electrical circuit, would they be in series or parallel? What constitutes the generator?

A

Parallel

Na+/K+ pump

74
Q

Why does it take time for the voltage to attain its max and back to min? How is this measured?

A

Because of capacitance! Time constant = amount of time it takes to charge and discarge the membrane capacitance

Time constant = Rm . C

  • Rm = membrane resistance
  • C = capacitance
75
Q

What does the time constant conceptually mean for the capacitor?

A
  • At time t, the charge on the initially charged capacitor is 63% of its max value
  • At time t, the charge on the initially charged capacitor is reduced to 37% of its max value
76
Q

What is the slope of V vs I?

A

Conductance, G

77
Q

Write out the conductance equation when GNa = GK?

A

Vm = (ENa+ EK) / 2

78
Q

What is the role of the Na/K-ATPase pump? What would happen without it?

A

To make sure concentration gradients are maintained.

Without it concentration gradients would disappear over days.

79
Q

If the ratio of Na+:K+ pumps is 1:100, when will the effect of the Na+ pump be the greatest?

A

When [K+] is low

80
Q

What represents the capacitor in a cell?

A

Membrane lipids are the insulator and the 2 ion containing solutions on either side are the parallel plates

81
Q

What does the time constant mean for conduction velocity?

A

SMALL TIME CONSTANT = FASTER VELOCITY

82
Q

What does the space constant mean for conduction velocity?

A

LARGE SPACE CONSTANT = HIGH VELOCITY

83
Q

How is the partition coefficient affected by hydrophobicity and hydrophilicity?

A

Higher if hydrophobic

Lower if hydrophilic

84
Q

Why is RMP closer to that of the EK+?

A

Because there are more K+ leaky channels than Na+ leaky channels

85
Q

How does permeability affect the GHK equation?

A

Higher permeability = more ion channels = larger effect on Vm

86
Q

What are the 4 common properties of ion channels?

A
  1. Amount of current that can flow: depends on the voltage applied and an intrinsic property called “the conductance” that is the inverse of resistance.
  2. Mean open time: how long the channel stays open on average
  3. Frequency of opening: how long are the average closing intervals are
  4. Selectivity of the channel for ions: determines which ions flow through
87
Q

Describe the effect of capacitance on current.

A

It minimizes the number of ions that move for each voltage change across the membrane

88
Q

Describe the movements possible/impossible in a phospholipid bilayer.

A

Translational mvt: possible

Lateral mvt: impossible

Attached with scaffolding proteins: no movement possible

89
Q

Why do we say that ion channels propose like hybrids?

A

They use size and loose interior binding sites to select for ions

90
Q

Do all ion channels bind ions on their interior?

A

NOPE

91
Q

Describe the structure of voltage-gated ion channels.

A

6 transmembrane helices with the 5th one being the P-loop

92
Q

Can conductance be negative?

A

NOPE

93
Q

By how much can an AP depolarize a cell?

A

+120 mV

94
Q

How does cell size affect capacitance?

A

Increased cell size = increased capacitance

95
Q

What is the RMP created by and maintained by?

A

Created by leakage K+ channels and maintained by Na+/K+ ATPase

96
Q

What does oubain do to a cell? To its RMP?

A

Inhibits the Na+/K+ ATpase pump

Polarized RMP

97
Q
A
98
Q

What is the difference between equilibrium potential and reversal potential? When are they equal?

A

Reversal Potential is determined in a voltage clamp experiment as the potential where the current changes direction.

Equilibrium Potential is defined by Nernst equation.

When a current is caried by a single ion (i.e Voltage gated Na channels) the Reversal potential is the same as the Equilibrium Potential for that ion

99
Q

Does osmosis require aquaporins?

A

Yes!

100
Q

Is glycerol lipid soluble?

A

YUP

101
Q

What would the RMP be if a cell is only permeable to K+?

A

-60 mV

SMP - MCP Exam 2 (13 decks)

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