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NEURO 0010 > Lectures 2-3 : Resting Membrane & Action Potential > Flashcards

Lectures 2-3 : Resting Membrane & Action Potential Flashcards

1
Q

what is important about the phospholipid bilayer?

A

has hydrophilic heads with hydrophobic tails → does not allow most ions through except using proteins and ion channels

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2
Q

why is water important?

A
  • water is the main ingredient in the intra and extracellular fluid
  • water is a polar solvent so molecules like NaCl will separate
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3
Q

what are ions and why are they important?

A
  • molecules that have a net electric charge
  • insulated by spheres of hydration
  • charge is determined by difference between protons and electrons
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4
Q

what are proteins made of?

A
  • sequences of amino acids (connectivity is determined by R group)
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5
Q

how do ions diffuse across the cell membrane?

A
  • protein channels span the cell membrane, and are made up of several subunits which form a pore
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6
Q

what are the states of the ion channels?

A

open & closed

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7
Q

what parts of the protein pore is hydrophilic vs hydrophobic?

A

parts that contact extracellular fluid and cytosol = hydrophilic
parts that span membrane = hydrophobic

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8
Q

what are the 2 important properties of a pore?

A
  • selectivity = the size and charge of the pore determines the ions
  • gating = many ion channels can open or close based on the microenvironment (can open in response to ligand binding or change in voltage)
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9
Q

what does resting membrane potential depend on?

A
  • relative ion concentrations inside and outside of the cell
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10
Q

what are the ion concentrations in axoplasm and extracellular fluid?

A
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11
Q

how are ion concentration gradients established and maintained?

A
  • sodium-potassium pump
  • 3 Na out / 2K in
  • runs constantly at constant rate
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12
Q

what is important about pump?

A
  • moves ion against their gradients
  • takes up 30% of all ATP and 70% of brain ATP
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13
Q

what does the calcium pump do?

A
  • transports Ca out of cytosol into extracellular fluid
    (important for synaptic transmission)
  • pumps Ca ++ into organelles like mitochondria
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14
Q

what are the two membrane forces?

A

diffusion/ gradient
- molecules prefer to move from an area of high to low concentration
- this process requires an open channel for the ion to move/diffuse through

electricity
- electrical current = conductance x electrical potential

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15
Q

what do you need for an ion to move across the channel?

A
  • open channel for the membrane to cross
  • a difference in the electrical potential across the membrane
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16
Q

what does Vm represent?

A

the charge of the inside of the membrane in comparison to the outside

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17
Q

when is equilibrium reached?

A

diffusion force = electrical force

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18
Q

equilibrium potential sign meanings?

A

pos = move in
neg = move out

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19
Q

what is the reality of asymmetrical charges?

A
  • the asymmetry in the number of ions on the two sides of the membrane involves a small percentage of all ions
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20
Q

driving force formula?

A
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21
Q

what happens to driving force when Vm = Eion

A
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22
Q

positive vs. negative driving force?

A

pos = ions pushed out of cell
neg = ions pushed into cell

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23
Q

driving forces of k and na (neg, 0, pos)?

A
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24
Q

how is Eion predicted?

A

Nernst equation

out/in

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25
Q

what happens when ion in is greater than ion out?

A

fraction is greater than 1 = neg Eion

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26
Q

what happens when ion out is greater than ion in?

A

fraction is less than 1 = pos Eion

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27
Q

how can u calculate membrane potential?

A

GHK formula
- based on the relative concentration gradients
- dependent of permeability of an out/in

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28
Q

Ohms Law?

A

current = (conductance) (Vm)
voltage = (current) (resistance)

29
Q

current formula?

A

current = (driving force) (contuctance)

30
Q

driving force meaning?

A

energy pushing ions in or out of cell

31
Q

ionic conductance meaning?

A

the capability of an ion to cross a membrane

32
Q

ionic current meaning?

A

ion movement across membrane

33
Q

what is a k+ mutation?

A

Weaver mice
- K+ channel mutation, allows the channel to pass both K+ and
Na
- Because of increased Na+ permeability, resting potential is more positive than normal and neuron function is compromised
- Called Weaver, because the mutation causes abnormal posture and movement, they die pre-maturley

34
Q

what is the purpose of an action potential?

A
  • encode all information in the nervous system
35
Q

what is an action potential?

A

a rapid increase in membrane potential
= depolarization of the cell

  • all or nothing
  • important for information transfer between neurons
36
Q

why do they occur?

A
  • axons are long
  • axoplasm is a poor conductor
  • axons are leaky
37
Q

what are the phases of an action potential

A
38
Q

when is the membrane negative vs. positive in an action potential

A
39
Q

what is the action potential threshold?

A

-40 mV

40
Q

what happens when one steps on a thumbtack?

A

1) sensory input
2) physical energy leads to change in Vm

41
Q

what determines AP firing rate?

A
  • degree of depolarization
42
Q

how is information coded?

A
  • in firing rate
  • different parts of the brain respond to different sensory inputs, memories, emotions etc
    (even within a brain area, different cells respond with greater or fewer action potentials to different inputs)
43
Q

what are the 4 channels involved in an action potential?

A

1) K leak
2) K voltage
3) Na voltage

44
Q

what is K leak channel responsible for?

A
  • how close Vm
    (how it is 40x more permeable to Na and Vm is closer to Ek)
45
Q

what are the 2 things that are always happening in the cell?

A
  • Na/K pump
  • K leak channel
46
Q

where are Nav and Kv channels located?

A

in the axon membranes

47
Q

where are the most Na voltage channels located on neuron?

A

Axon Hillock

48
Q

what is the NaV channel?

A

a pore in the membrane that is highly selective for Na+ and dependent on changes in the membrane voltage

ball and chain

49
Q

ball chain steps and corelation with AP?

A

1) open with little delay when Vm reaches threshold (activation)
2) they stay open for about 1 msec and then close b/c ball swings over opening (inactivation)
3) they cannot be open again until Vm is below -65 in undershoot phase (deinactivation)
4) channels can open again

50
Q

Kv channels steps?

A

1) Open in response to depolarization
but only 1 msec later (not
immediately like VG Na+ Channels)

2) Opening of VG K+ Channels → K+
flows down concentration gradient and outside the cell → hyperpolarization (counteract depolarization of AP in order to repolarize neurons i.e. return peak membrane potential towards negative resting Vm)

51
Q

what are the 2 ways that threshold can be reached?

A

1) transduction
2) signaling from NT

52
Q

Resting state steps?

A
53
Q

Passive Depolarization?›

A
54
Q

Rising phase?

A
55
Q

Overshoot?

A
56
Q

Falling phase?

A
57
Q

Undershoot?

A
58
Q

Absolute and relative refractory periods?

A
59
Q

Rare diseases due to ion channel mutations? (3)

A

Generalized epilepsy with febrile seizures
– seizures start in early childhood
– Na+ channel mutations
– slow Nav inactivation -> neurons are hyperexcitable

Benign familial neonatal convulsion
– frequent brief seizures
– K+ channel mutations
– reduced K+ current in AP falling phase -> neurons are

Episodic ataxia
– episodes of poor coordination of movement and balance (ataxia)
– various K+ channel mutations impair AP repolarization

60
Q

Ion channel toxins 2

A

Tetrodatoxin (TTX)
* puffer fish (“fugu”) ovaries, liver, intestines (from ingested bacteria)
* 23 people have died since 2000 in Japan from fugu consumption
* x1200 more toxic than cyanide and no antidote
* blocks Na+ channels and stops action potentials (1mg is lethal)
* muscle paralysis -> asphyxiation

Saxitoxin (STX)
* poisoned by eating shell fish that have ingested
dinoflaggelates (algae)
* x100 more lethal than sarin nerve gas
* CIA suicide pills
* also blocks Na+ channels and action potentials

61
Q

Local anesthetics?

A
  • locally block APs
  • cocain - lidocain
  • block Na+ channels
  • APs in small axons are affected most
  • most pain nerves are small
62
Q

how do APs affect other neurons?

A
  • the AP must propagate to the axon terminal and synapses
  • inflow of Na+ ions will depolarize neighboring patches of membrane to threshold
  • propagation is one way due to refractory period
63
Q

more current flow down — axons

A

wider

64
Q

larger axons conduct APs —

A

faster

65
Q

what are the two paths that positive charge can take?

A
  • inside axon
  • across axonal membrane
66
Q

relationship with 2 axon pathways?

A

increase diameter - more current down axon

fewer open membrane pores - more current down axon

67
Q

MS facts?

A

degrades mylein, disrupting AP conduction

targets oliodengrolia CNS

women are 2-3 times more likely to have MS

affects .02% of general population

siblings 5% - identical twins 31%

environmental factors
- temp, climate, low vitamin D, smoking

68
Q

MS symptoms?

A
  • numbness
  • weakness
  • electric shock sensations
  • fatigue
  • blurred vision

NEURO 0010 (22 decks)

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