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Neuroscience 3800 > Chapter 4 - The Action Potential > Flashcards

Chapter 4 - The Action Potential Flashcards

1
Q

passive processes

A

diffusion

electrostatic gradient

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2
Q

movement of electrical charge

A

I: current

measured in Amps (A)

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3
Q

relative ability for the charge to migrate

A

g: Conductance

measured in Siemens (S)

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4
Q

inability of the charge to migrate

A

R: Resistance

measured in Ohms

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5
Q

difference in charge between anode and cathode

A

V: Electrical potential

measured in Volts (V)

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6
Q

electrical current flow across a membrane

A

Ohms law

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7
Q

Ohms law

A

I = gV

I = current 
g = conductance 
V = voltage (difference in charge)
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8
Q

The action potential has four important qualities

A

1) There is a threshold for initiation
- the Vm changes as a function of Ohms law
- (V=Ig or V = IR)

2) The action potential is all-or-none
3) The action potential conducts without decrement
4) The action potential is followed by a brief refractory period

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9
Q

cross threshold value for action potential to occur

A

All-or-none

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10
Q

Chain of events that initiates the action potential

A
  • opens Na + permeable channels
  • Na+ influx ->
  • reaches threshold ->
  • action potential
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11
Q

firing frequency reflects the _______

A

magnitude of the depolarizing current

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12
Q

max Hz for action potential ____

A

1000 Hz

depends on the absolute and refractory periods

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13
Q

I(ion) = ?

A

I (ion) = g(ion) [Vm-E(ion)]

I = current (Ionic current)
movement of electrical charge

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14
Q

holds voltage of membrane constant, measures current.

Inward (down) and outward (up) current measurements

A

Voltage clamp

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15
Q

the accumulation (or removal) of electrical charges on the electrode and in the salt solution

A

capacitive current

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16
Q

persistant outward current

always letting ions leak through
independent of membrane potential

A

leakage current

leak channels

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17
Q

selective voltage K+ channel blocker

A

TEA

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18
Q

neurotoxin found in puffer fish

blockage voltage Na+ channels

A

TTX

another: saxitoxin (red tide)

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19
Q

transient increase in g(Na)
influx of Na+ ions
- inside the membrane has negative electric potential so there is a large driving force on Na+ ions. Therefore, Na+ ions rush into the cell through Na+ channels, causing the membrane to rapidly depolarize
- rapid depolarization

A

rising phase

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20
Q

increase in g(K)
efflux of K+ ions
- voltage-gated Na+ channels inactivate. Voltage-gated K+ channels open (1msec after depolarization). Greater driving force on K+ ions when membrane is strongly depolarized. K+ rushes out of the cell. Membrane potential gets more negative.
- rapid repolarization

A

falling phase

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21
Q

With increasing depolarization using voltage clamp the K+ current _______

A

increases due to g(k) and (Vm - E(K))

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22
Q

as the Vm begins to depolarize, the Na+ current becomes increasingly ______

A

inward
as Vm approaches E(Na) (+55mV) the inward I(Na) starts to decrease due to a decrease in driving force (Vm-E(Na))
at further depolarization (>55m V) the I(Na) will reverse

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23
Q

after-hyperpolarization (AHP) phase

A

K+ driven outwards, and towards E(K)

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24
Q

g(Na) turns on and off more ____ than potassium channels (gK)

A

rapidly

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25
Q

what makes up the components of ion current?

A

conductance (how easily it moves) and

driving force

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26
Q

equilibrium state for membrane potential of K+

A
  • 80 mV
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27
Q

equilibrium state for membrane potential of Na+

A

+ 55 mV

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28
Q

if we have a lipid bilayer with closed channels in the membrane, what can we say about current levels?
conductance of K+?

A

no conductance - equation = 0

no current

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29
Q

current clamp inject _____ and measure _____

A

current clamp injects current and measures voltage

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30
Q

voltage clamps inject ____ and measure _____

A

voltage clamp injects voltage and measures current

31
Q

you can determine current by knowing ___ and ____

A

you can determine current by knowing resistance and current

32
Q

holds voltage of membrane constant, measures current

A

voltage clamp

33
Q

come down past membrane potential - drive for K+ to reach E(K+) after hyperpolarization stage

A

AHP (after-hyperpolarization)

34
Q

what is faster, K+ or Na+ ?

A

Na+ is faster

35
Q

Voltage-Gated Sodium Channel

A

structure-transmembrane domains and ion-selective pores

  • 4 domains
  • each domain = 6 transmembrane a-helices
  • pore loop-filter (what makes it slective; they recognize voltage changes)
  • pore closed at RMP
  • molecule twists to allow Na+ through the pore
  • voltage sensor (S4): senses changes in membrane voltage; makes it go from closed to open channel
36
Q

senses changes in membrane voltage (voltage gated sodium channel)
- makes it go from closed to open channel

A

Voltage sensor (S4)

37
Q

measures current through a single channel
hold voltage, measure current through channel on end of electrode

  • studies ionic current single channels
A 
Patch clamp (like voltage clamp) 
- can look at how membrane functions at different voltages
38
Q

largest channels

A

voltage-gated channels

39
Q

several stimuli control the opening/closing of ion channels

A
  • ligand-gated
  • phosphorylation gated (cells that change_
  • voltage-gated (largest channels)
  • stretch (mechanical) - (autotory/sematosensory system)
40
Q

direction of current is dependent on ____

A

direction of current is dependent on membrane voltage

41
Q

Plot current versus the potential difference of membrane
I is linearly related to voltage
- you can look at and calculate current by conductance or resistance

A

Ohmic channel

42
Q

positive charge flowing into the cell, or negative charge flowing out of the cell

A

inward current

43
Q

positive charge flowing out of the cell, or negative charge flowing into the cell

A

downward current

44
Q

sodium channel inactivation

A

1) close channel
2) depolarization - open; voltage change, Na+ comes in
3) Inactivation - (globular) protein blocks channel
4) deinactivation: takes time until it dissociates from channel - cannot activate channel when protein is there/ blocks neuronal firing.

45
Q

functional properties of the Na+ channel

A
  • open with little delay (fast firing)
  • stay open for about 1 millisecond
  • cannot be open again by depolarization
46
Q

channels are inactivated (blocked by protein)
cannot be opened, even at high stimulation
- Na+ channels inactivated. Membrane potential goes back to a more negative value closer to threshold value.

A

absolute refractory period (voltage-gated Na+ channels)

47
Q

some channels are inactivated, mane are deinactivated
neurons can fire with increased stimulation
- Membrane potential stay depolarized until K+ channels close.

A

relative refractory period (voltage-gated Na+ channels)

48
Q

delayed opening channels that repolarize the membrane
- another term for the voltage-dependent K+ channels that open ~ 1msec after the onset of an action potential to repolarize the membrane

A

delayed rectifiers

49
Q

types of voltage dependent K+ channels

A

1) delayed rectifiers
2) Ca 2+ activated K+ channel
3) a fast-transient K+ channel
4) M-type K+ channel - slow, inactivated by ACh

50
Q

proposed voltage sensory

A

S4 region

51
Q

impulse traveling in the normal direction in a nerve fiber

action potential travels in one direction

A

orthodromic

52
Q

impulse traveling in the opposite direction to that normal in a nerve fiber
backward propagation

A

antidromic

53
Q

duration of action potential

A

~ 2 msec

54
Q

typical conduction velocity

A

~ 10-12 m/sec

55
Q

two directions ions can go

A

down the cytoplasm

out the membrane into extracellular space

56
Q

facilitates current flow

  • effectively increases size of membrane 100x - increases resistance
  • channels (V-D and leak) only at the Nodes of Ranvier
A

myelin

57
Q

myelinating cells

A

Schwann cells in PNS

oligodendroglia in CNS

58
Q

a gap in the myelin sheath of a nerve, between adjacent Schwann cells

A

Nodes of Ranvier

59
Q

is the propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials.
- high density of Na+ V-D at Nodes of Ranvier

A

Saltatory conduction

60
Q

autoimmune
degeneration of myelin in CNS
without myelin, the spread of + charge is diminished

A

multiple sclerosis

61
Q

the transfer of information from one neuron to the other

A

synaptic transmission

62
Q

because relative permeability of membrane greatly favors Na+, the membrane potential goes to a value close to Ena, membrane potential is above 0 mV (positive)

  • inside is negative with respect to outside
A

overshoot

63
Q

K+ channels are at resting K+ membrane permeability. Membrane potential goes towards Ek which causes hyperpolarization until K+ channels close
- hyperpolarization

A

undershoot

64
Q

_______ of action potential reflects the magnitude of depolarizaing current

A

firing frequency

65
Q

maximum firing frequency

A

1000 Hz

66
Q

membrane potential at which enough voltage-gated Na+ channels open so that they relative ionic permeability of the membrane favors over K+

  • critical level of depolarization that must be crossed to trigger action potential
A

threshold

67
Q

diseases caused by disturbed function of ion channel subunits or the proteins that regulate them. These diseases may be either congenital (often resulting from a mutation or mutations in the encoding genes) or acquired (often resulting from autoimmune attack on an ion channel).

A

channelopathy

68
Q

Voltage-gated Potassium channels

A

4 subunits

pore loop: channel selectively permeable to K+ ions

69
Q

Importance of regulating extracellular K+

A

at rest - membrane mostly permeable to K+, membrane potential is closer to Ek

  • sensitive to changes in [K+]o
  • increase in extracellular K+ will lead to depolarization of membrane
    ( x10 [K+]o 5-> 50mV; Vm: -65 -> -17mV) depolarization
  • blood brain barrier: limits K+ movement into external cellular environment
  • K+ spatial buffering (astrocytes) - K+ pumps take up K+, K+ channels.
70
Q

another term for axon hillock
Its the area where the soma ends and the axon starts

in a typical brain or spinal neuron, depolarization of the dendrites and soma caused by synaptic input leads to the generation of action potential if the membrane of the axon hillock is depolarized beyond threshold

A

spike initiation zone

71
Q

Direction of current (Im) is dependent on

A

Vm (membrane potential)

72
Q

Current is linearly related to

A

voltage

73
Q

current is linearly related to voltage

because you can go through, look at and calculate current by conductance or resistance

A

Ohmic channel

74
Q

increasing size of membrane increases

A

resistance

Neuroscience 3800 (5 decks)

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