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Neuro 3000 > Action Potentials > Flashcards

Action Potentials Flashcards

1
Q

Open when membrane is depolarized, slow inactivation, depolarizes after AP

A

Delayed rectifier K channel

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2
Q

Where is the selectivity filter of the VG Na channel?

A

The loop between subunits 5 and 6

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3
Q

What initiates closure of the inactivation gate in VG Na channels?

A

Outward movement of S4 (voltage sensor)

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4
Q

Many properties displayed by the AP are due to properties of this channel

A

VG Na channel

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5
Q

How does water play an important role in determining selectivity of the VG Na channel pore?

A

The size of a partially hydrated Na ion can fit but a partially hydrated K ion cant

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6
Q

What are used to record APs?

A

Intracellular and extracellular electrodes

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7
Q

What happens in the rising phase?

A

Na going into the cell, high Na conductance (how easy it is for ions to move), inside becoming positive

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8
Q

From puffer fish, block VG Na channel

A

Tetrodotoxin

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9
Q

What happens in the falling phase?

A

ABSOLUTE REFRACTORY. Na channels close and won’t open, K channels open, high K conductance

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10
Q

Sea anemone toxins are active here

A

Site 3

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11
Q

When the AP looks like it is jumping from noble to node

A

Saltatory conduction

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12
Q

Channel with selective ion conductance for Na

A

VG Na channel

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13
Q

When AP conduction is started from the end and moves toward cell body (rare)

A

Antidromic

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14
Q

Are the a helical segments of the VG Na channel

A

S1-S6

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15
Q

These two things help convey info about the neuron ion channels

A

Rate and pattern of firing

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16
Q

Set by K channels

A

Relative refractory period

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17
Q

These two VG channels structures are related

A

VG K and VG Na channels

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18
Q

Why cant an AP be faster than 1 ms?

A

The absolute refractory period

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19
Q

When do toxins have an effect on the VG Na channel?

A

When there is an AP. No effect if it is at rest

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20
Q

Opening the inactivation gate is also tied to doing what with it?

A

Closing it

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21
Q

What is deinactivation of the inactivation gate and when does it occur?

A

It is when the VG Na channel is not activated and the ball and chain falls out. It happens around -65 mV

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22
Q

Tetrodotoxin and saxitoxin are active here

A

Site 1

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23
Q

The voltage sensor of the VG Na channel that moves outward when the cell depolarizes

A

S4

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24
Q

What does tetraethyl-ammonium do to cells?

A

Blocks K current outward

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25
Q

What happens to channels behind the AP that the AP has already passed?

A

They are refractory bc Na channels are inactivated

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26
Q

When AP conduction is started from the cell body

A

Orthodromic

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27
Q

Block pore and selectivity filter, specific amino acids required

A

Tetrodotoxin and saxitoxin

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28
Q

What is length constant?

A

How far current flows before it leaks out, before it is reduced to 37%

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29
Q

Used to deduce the nature of the AP

A

Voltage clamp and squid giant axon

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30
Q

Segment of VG Na channels that mostly line the pore

A

S6

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31
Q

These don’t open right after depolarization, they are delayed

A

VG K channels

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32
Q

Composed of 4 subunits, each similar to one domain of the VG Na channel

A

VG K channels

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33
Q

Axon placed in saline solution, reference electrode in solution, electrodes hooked up to ultimately measure current at specific voltages

A

Voltage clamp

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34
Q

From a dinoflagellate, occurs in calms, shellfish, and mussels. Block VG Na channel

A

Saxitoxin

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35
Q

Na channels inactivated, cant be deainactivated until Vm is more negative

A

Absolute refractory period

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36
Q

This gate is less accessible after depolarization in the VG Na channel

A

Inactivation gate

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37
Q

What does I ion = g ion represent?

A

Current of the ion = conductance of the ion (Like Ohms law Vm - Eion)

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38
Q

What is needed to initiate an AP?

A

Depolarization of membrane due to generator potentials beyond some threshold (around -40 mV)

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39
Q

What are spike initiation zones?

A

In unmyelinated neurons, they are areas of high Na channel concentration

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40
Q

Part of the VG Na channel sensitive to proteases and antibodies

A

Inactivation gate

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41
Q

Used voltage clamp to determine ionic permeability changes during the AP

A

Hodgkin and Huxley

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42
Q

VG Na channels contain 4 of these

A

Four homologous domains

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43
Q

What is the maximum rate of an AP?

A

1000 Hz = 1 ms

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44
Q

Na channels inactivate, K channels open, large driving force for K to leave cell

A

Falling phase

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45
Q

Toxins that affect channel inactivation

A

Scorpion and sea anemone toxins

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46
Q

Techniques used to record electrical activity from single neurons or single channels

A

Patch clamp techniques

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47
Q

What are membrane conductance changes dependent on?

A

Time and voltage

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48
Q

Set by Na channels

A

Absolute refractory period

49
Q

How does depolarization occur as the AP moves down the axon?

A

Successive patches of membrane are depolarized

50
Q

These segments of VG Na channels move in specialized channels

51
Q

These areas contain many VG Na channels

A

Nodes of Ranvier

52
Q

Mechanistic models of this channel were developed in the 1960s and 1970s

A

VG Na channels

53
Q

These studies support S4 as voltage sensor because cysteine mutations showed outward movement

A

Mutagenesis studies

54
Q

AP conduction moves down the cell in how many directions?

A

One direction

55
Q

Sigma conotoxins are active here

56
Q

What happens to the concentrations of Na and K inside and outside the cell during an AP?

A

The relative concentrations stay the same even though Na flows in and K will flow out. K still higher in and Na still higher out

57
Q

What does lidocaine do in the VG Na channel?

A

Blocks the inside channel (S6 segment)

58
Q

This was used to examine the biophysical properties of individual Na channels

A

Patch clamp technique

59
Q

What are generator potentials also known as and what do they do?

A

EPSPs. Bring the cell to threshold (-40 mV)

60
Q

What are total Na and K currents composed of?

A

The sum of individual currents

61
Q

What does the undershoot represent?

A

Relative refractory

62
Q

How does the voltage sensor (S4) fit in each domain?

A

Slides within a channel in each domain

63
Q

From frog, channels open at more negative voltages, stay open too long

A

Batrachotoxin

64
Q

Vm (membrane potential) moves towards EK (eq pot for K), hyperpolarizing cel, little permeability to Na, opening of Ca activated K channels

A

Undershoot

65
Q

Segments of VG Na channel that form inner pore

66
Q

SLIDES 14-18 GRAPHS

A

SLIDES 14-18 GRAPHS

67
Q

What allows the cell to depolarize?

A

The faster opening of Na channels than K channels so K cant dominate and the cell becomes positive

68
Q

What does myelin reduce?

A

Membrane capacitance

69
Q

The falling phase of APs is also due to the opening of these, not just the closing of Na channels

A

Opening of K channels

70
Q

Maintained by Na-K-ATPase

71
Q

An important type of K channels in APs and hyperpolarization

A

Delayed rectifier channels

72
Q

Used to see what current is flowing at specific voltages

A

Voltage clamp

73
Q

Many types of these, 80 subunit genes, multiple families

A

K channels

74
Q

Are a brief reversal of charge (not gradients) in which the inside becomes briefly more positive than the outside

75
Q

What makes up the VG Na channel?

A

One protein with 4 domains that make it look like 4 proteins, this is the alpha subunit and there are B1 and B2 subunits on the ends

76
Q

Also known as spike, discharge, nerve impulse

77
Q

What is the goal of an AP?

A

Ultimately stimulate the release of NTs

78
Q

Is a wave of positive charge transmitted down the neuron

79
Q

Vm hyperpolarized until K channels close

A

Relative refractory period

80
Q

The time when more current is required to fire AP

A

Relative refractory period

81
Q

Local anesthetics block in these segments of the VG Na channel

82
Q

How does myelin help propagation?

A

Increasing length constant (how far current flows before it leaks out - reduced to 37%)

83
Q

Frequency and pattern of these encode info

84
Q

AP conduction is propagated without doing what?

A

Decreasing strength

85
Q

Used to look at the electrical activity of one channel

A

Patch clamp technique

86
Q

Due to outward K current

A

Falling phase

87
Q

Channel with two gates, including an inactivation gate that closes after about 1 ms and only opens when the cell returns to a more negative voltage

A

VG Na channels

88
Q

What is required for fast inactivation in the VG Na channel?

A

3 key amino acids

89
Q

What does an extracellular electrode oscilloscope display?

A

A dip to more negative (Na in), then a spike to above the resting to be a little positive (K out with overshoot), and then back to resting (different than normal AP curve)

90
Q

Toxins used to isolate a, B1, and B2 subunits in mammalian brain, a and B1 in skeletal muscle, eel a in this channel

A

VG Na channels

91
Q

These are used to study the function and structure of the VG Na channel

92
Q

What does the amount of depolarization control?

A

The firing frequency. More depolarization = more APs (all are always the same size)

93
Q

What does tetrodotoxin do to cells?

A

Block Na current inward

94
Q

Channel with rapid inactivation (open 1 ms)

A

VG Na channel

95
Q

All chemical transmission depends on these

96
Q

What happens 1 ms after Na channels open in the AP?

A

Na channels close and the K channels open causing the cell to rapidly hyperpolarize

97
Q

What is conductance?

A

How easy it is for ions to move

98
Q

Vm (membrane potential) approaches ENa (eq pot for Na) greater than 0 mV

99
Q

What does the inactivation gate form with the gate receptor in the VG Na channel?

A

It forms a hydrophobic interaction with it

100
Q

Why was the squid axon used to study APs?

A

It is 800 um in diameter compared to humans 2 um. Easy enough to see and manipulate

101
Q

What are AP firing patterns due to?

A

Type/combination of ion channels present

102
Q

Why cant the membrane depolarize the area before an AP it just passed over?

A

It is in the absolute refractory period

103
Q

Reentrant loop forms pore here in the VG Na channel

A

Between 5 and 6 of each domain

104
Q

How does the inactivation gate of the VG Na channel work?

A

Closes after 1 ms and only opens when the cell returns to a more negative voltage

105
Q

Na ions enter cell due to large driving force

A

Rising phase

106
Q

What does an intracellular electrode oscilloscope display?

A

A spike up to a positive charge and a fall back down to negative with a little undershoot (Na in, K out, normal looking AP curve)

107
Q

What are the B subunits required for in the VG Na channels?

A

Required for normal kinetics and voltage dependence of gating

108
Q

Channel with voltage dependent activation (around -40 mV)

A

VG Na channel

109
Q

Biochemical approaches led to the discovery of the proteins that make up this channel in 1980

A

VG Na channels

110
Q

Caused by influx of Na ions through VG Na channels open for about 1 ms

A

Depolarization

111
Q

Vm (membrane potential) at which Na channels open, more permeable to Na

112
Q

At what voltage does the VG Na channel open?

113
Q

Caused by efflux of K ions through VG K, brings cell back to -65 mV

A

Repolarization

114
Q

Produced by entry of positive charges into the cell

A

Generator potential (small changes in voltage)

115
Q

Contain immunoglobulin like folds (look like antibodies) in VG Na channel

116
Q

What are intracellular and extracellular recordings measured in?

A 
Intra = mV
Extra = uV
117
Q

Brevetoxins and ciguatoxins are active here

118
Q

What does a more excited cell have in terms of APs?

A

More APs, more frequency, not bigger APs

119
Q

Due to inward Na current

A

Rising phase

Neuro 3000 (15 decks)

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