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BIOL 367 > Neurons as Electrical Elements > Flashcards

Neurons as Electrical Elements Flashcards

1
Q

What is neuro-electricity due to?

A

ionic currents that are generated by the diffusion of 4 essential ions (Na+, K+, Ca2+, Cl-)

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2
Q

What is the difference between a passive and an active electrical signal?

A
  • active (regenerative) response results from an action potential
  • a passive response may be a hyperpolarization or depolarization but does not result in an action potential
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3
Q

Where does the non-zero voltage difference (membrane potential) come from?

A

uneven distribution of charged molecules inside and outside of selectively permeable cell surface membrane

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4
Q

When is the voltage at 0?

A

when depolarizing or dead

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5
Q

How are changes in voltage across the membrane produced?

A

changing the selective permeability of the membrane for different ions

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6
Q

What is the role of pumps/transporters in setting membrane potentials?

A
  • responsible for ionic movments across neuronal membranes
  • active transporters: move ions against concentration gradient
  • ion channels: allow ions to diffuse down electrochemical gradient
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7
Q

When is there an actual energy source?

A

when we have a concentration gradient and if ion is out of its electrochemical “equilibrium condition”

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8
Q

What is the electrochemical “equilibrium condition” determined by?

A

concentration, charge, and voltage differences

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9
Q

What is needed to “harvest” the energy?

A

permeability is needed to generate “voltage”

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10
Q

At equilibrium chemical and electrical forces are:

A

equal and opposite and net diffusion is zero

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11
Q

What is the “equilibrium potential”?

A
  • the particular voltage where the forces balance
  • Ex = equilibrium potential of ion x
  • also known as reversal potential
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12
Q

How do we calculate the equilibrium potential?

A
  • calculated as “Nernst” potential
  • outside over inside
  • gives us V of inside relative to outside
  • Veq or Eion
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13
Q

What does 2.303 RT/F equal at 18, 37, and 10 degrees celcius?

A
  • 0.058 V (58 mV) @ 18
  • 0.062 V @ 37
  • 0.056 V @ 10
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14
Q

What is z?

A

ion’s valence (+1, +2, -1, -2)

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15
Q

What is the voltage change not accompanied by a measurable change in concentration?

A

only a small fraction of the total ions in the compartments have to re-distribute to create the gradient

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16
Q

What is the nernst equation?

A

Veq = +(2.303RT/zF) * log ([ion1]o/ +[ion1]i)

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17
Q

Why is there a need for the Goldman-Hodgkin Katz (GHK) equation?

A

because real neurons have more than just one permeant ion species

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18
Q

What is the GHK equation?

A

Vm = +(2.303RT/zF) * log((Pion1[ion1]o + Pion2[ion2]o) / (Pion1[ion1]i + Pion2[ion2]i)

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19
Q

What is P?

A

P refers to the permeability of the ion species relative to each other

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20
Q

When does the membrane potential change?

A

1) permeability changes for one or more ionic species (electrical and fast)
2) concentration of an ionic species changes
3) activity of electrogenic pump changes

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21
Q

What happens if the conductance (permeability) of the membrane for an ion(s) is increased?

A
  • the membrane potential will change so that it is closer to the equilibrium (Nernst) potential for that ion(s)
  • current will flow to move the membrane potential closer to Eion
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22
Q

What is the equation for ionic current?

A

Iionx = gionx * (Eionx - Vm)

  • driving force: Ex - Vm
  • gx: total conductance (# of open channels)
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23
Q

What is the driving force?

A

difference between the voltage at the moment and the equilibrium potential

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24
Q

What is another term for permeability?

A

conductance

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25
Q

If the conductance of a membrane for an ion(s) is increased, what happens to the membrane potential?

A

the membrane potential will change so that it is closer to (but never beyond) the (Nernst) potential for that ion

26
Q

When the permeability of the membrane for an ion is increased, how will the current flow?

A

the current will flow so as to move the membrane potential nearer to Eion

27
Q

If the conductance is decreased, what happens to the membrane potential?

A

the membrane potential will be less influenced by the ion whose permeability is reduced (move towards combined Nernst potentials of other ions)

28
Q

What is Vm?

A

membrane potential at time 0

29
Q

What is Eionx?

A

equilibrium potential for ion x

30
Q

What occurs if there are “voltage” gated channels?

A

depolarization from pressure gated channels initiate further changes in permeability and thus voltage

31
Q

What are the problems with fig 2.6?

A

1) peak should not reach ENa
2) mostly due to time dependent properties of channels
3) where the permeability of Na decreases, the permeability of K increases

32
Q

What do the currents depend on?

A

depend on the driving force

33
Q

What does the driving force change with?

A

Vm

34
Q

What is the voltage-clamp technique used for?

A

to measure the current generated by the opening and closing of channels (even though voltage and current change at the same time)

35
Q

What does the current flow for each ion depend on?

A

1) force driving the ions

2) conductance

36
Q

What is the force driving the ions?

A

the difference between the voltage at the moment and the equilibrium potential

37
Q

What is the conductance for an ion?

A

number of open channels*single channel conductance

38
Q

When looking at an individual channel is there 100% probability it will open?

A

No, not identical action occurs every time

39
Q

What are the possible actions of individual Na channels?

A

quick to open, quick to close even when membrane is still depolarized (won’t reopen - inactivation)

40
Q

What are the possible actions of individual K channels?

A

slow to open, stay open until V is returned to negative potential

41
Q

What accounts for the differences in the actions of Na channels vs K channels?

A

Na channels have an inactivation gate

42
Q

An action potential is the result of:

A

fast activating inward Na conductance that turns off even though the membrane is depolarized and a slower activating K conductance that persists

43
Q

What are the passive properties of membranes important for?

A

1) action potential conduction

2) determine how synaptic inputs summate and are integrated

44
Q

What kind of conduction signals do passive membrane properties affect?

A

both active and passive conduction of signals

45
Q

What two aspects of voltage spread result from the physical properties of neurons?

A

1) space dependent property

2) time dependent property

46
Q

What is Rm and Cm and tau?

A

resistance and capacitance and membrane time constant

47
Q

What do the values of Rm and Cm depend upon?

A

depend on size of the neuron (larger cells have lower resistance and larger capacitances, and brief time constants)

48
Q

How does tau rely on the resistance and capacitance?

A

tau = Rm*Cm

49
Q

What is saltatory action potential conduction?

A

propagation of action potentials along myelinated axons from one node to the next

50
Q

How does myelinating the axon affect the resistance and therefore the time constant between nodes?

A

between the nodes there is very high resistance, so time constant is long and slow charging

51
Q

How does myelinating the axon affect the capacitance in the nodes?

A

C is small, so charges up fast

52
Q

What diameter of myelinated axon is equivalent to the conduction velocity of a squid axon (500 micrometer diameter)?

A

5-6 micrometer

53
Q

What is MS?

A

multiple sclerosis: demyelination, lesions

54
Q

What kind of sensory problems can a person with MS suffer from?

A

loss of sensitivity, prickling, numbness

55
Q

What kind of motor difficulties can a person with MS experience?

A

muscle weakness, clonus, muscle spasms, difficulty moving difficulty with coordination, problems with speech or swallowing

56
Q

What other symptoms can a person with MS experience?

A

visual, fatigue, acute or chronic pain, bladder and bowel difficulties, cognitive impairment, unstable mood

57
Q

How does MS affect the channels and axons?

A

loss of myelin leads to Na+ channel redistribution and breakdown of axons

58
Q

Ultimately, what does MS result in?

A

decreased conduction velocity and decreased ability to sustain firing

59
Q

What drug has potential for treating MS and what is it currently used for?

A

beztropine, currently used for Parkinson’s

60
Q

What effects does benztropine have that treat MS?

A

induces the differentiation of oligodendrocyte precursor cells (OPCs) and enhanced remyelination

BIOL 367 (4 decks)

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