Lecture 3 Flashcards
1
Q
Speed of depolarization:
A
about 1ms 1/1000th of a sec
2
Q
Speed of AP:
A
about 200 mph
3
Q
How many voltage gated channels are involved in the formation of APs?
A
2 Na (depolarize) and K (repolarize)
4
Q
What causes the termination of the AP?
A
Opening of the K channels
5
Q
T or F? APs are analog signals.
A
F. digital. Its there or it’s not
6
Q
This type of signal can very over an enormous range:
A
graded analog
7
Q
What produces the absolute and relative refractory periods?
A
recovery oft he Na and K channels
8
Q
T or F? It is possible to produce another AP during the relative refractory period.
A
T. Just requires a stronger stimulus
9
Q
What type of potentials are produces at the synapse?
A
graded
10
Q
T or F? Graded potentials can summate.
A
T
11
Q
T or F? APs can summate.
A
F
12
Q
This segment of the neuron has a very high concentration of sodium channels
A
trigger zone (initial segment)
13
Q
This type of potential is good at starting to produce a response that you can finely tune:
A
graded
14
Q
This type of potential can be used to compute things
A
graded
15
Q
T or F. Graded potentials (GP’s) do not diminish with distance.
A
F. They do diminish with distance
16
Q
What happens in GPs are above the threshold in the Trigger Zone?
A
they produce spikes
17
Q
Does a graded potential start below or above threshold?
A
Above
18
Q
Is a GP above or below the threshold at the trigger zone?
A
It depends on the initial strength of the stimulus.
19
Q
Will the release of Glu depolarize or depolarize a cell?
A
depolarize
20
Q
T or F? Na channels can be found all over the neuron.
A
F. localized in the trigger zone
21
Q
Why is there less positive charge as you get closer to the trigger zone with a graded potential?
A
Na leaks out and the inside will be less positive
22
Q
T or F? A weak stimulus will release little neurotransmitter and a strong stimulus will release more.
A
T
23
Q
Are APs generated along efferent or afferent neurons?
A
Afferent
24
Q
What is AP frequency proportional to?
A
Graded potential amplitude
25
What happens if the graded potential is just at threshold?
it will on ly produce a few APs
26
Can EPSPs (Excitatory post-synatic potential) produce APs?
Yes, if they are large enough
27
The strength of a stimulus is encoded in:
the graded potential
28
T or F? The bigger the graded potential, the higher the frequency.
T
29
A strong, graded potential will produce:
many APs at a high frequency
30
How can the frequency of APs be increased?
increase the strength of the graded potential
31
The size of the graded potential is proportional to:
the number of activated channels
32
T or F? Graded potentials can be both positive and negative
T. EPSP or IPSP
33
T or F? Naps have variable amplitude
F. Graded potentials do
34
Are graded potentials at the synapse fast or slow?
slow
35
Are APs at axon initial segment slow or fast?
fast
36
T or F? Graded potentials at synapse have a stereotyped response.
F. APs do
37
The polarity of this type of potential can vary:
graded potential
38
What encodes the strength of the stimulus in neurons?
spike frequency and EPSP amplitude of the synaptic current
39
Both of these will be lower with a mall graded potential in comparison to a large graded potential:
amplitude and spike frequency
40
T or F? The inside of the cell becomes more positive with an IPSP.
F. More negative
41
What type of signal does a graded potential get in a neuron?
input signal
42
What type of signal does a AP get in a neuron?
conduction signal
43
Where does a GP typically occur in a neuron?
dendrites and cell bodies
44
Where does an AP typically occur in a neuron?
trigger zone through an axon
45
What type(s) of gated ion channel are involved with graded potentials?
mechanically, chemically, or voltage-gated channels
46
What type(s) of gated ion channel are involved with APs?
Voltage-gated only
47
What ions are involved with GPs?
usually Na, Cl, and Ca
48
What ions are involved with APs?
Na and K
49
Does a graded potential (lead to?) a signal that is depolarizing or hyperpolarizing?
either
50
Does an AP (lead to?) a signal that is depolarizing or hyperpolarizing?
depolarizing
51
What does the strength of the signal of the GP depend upon?
initial stimulus, can be summed
52
What does the strength of the signal of the AP depend upon?
it is always the same (all-or-none), cannot be summed
53
What initiates the signal for a GP?
entry of ions through channels
54
What initiates the signal for a AP?
Above-threshold GP at the trigger zone
55
T or F? There is a minimum level required to initiate a GP/
F.
56
What is the initial stimulus strength indicated by for a GP?
frequency of a series of APs
57
T or F? All cell at rest will have no open channels.
F. some are open (leak channels), we don't know which
58
3 types of channels leading to an AP:
1. Unregulated (leak) channels produce the resting membrane potential
2. Synaptic, ligand-gated channels produce graded potential
3. Voltage gated channels produce the AP
59
What type of channel produces the resting membrane potential?
Unregulated, leak channels
60
What type of channel produces the graded potential?
Synaptic, ligand-gated channels
61
What type of channel produces the AP?
Voltage gated channel
62
What channels cause the undershoot?
K channels
63
What are the names of the two sides of the spike of an AP called?
Rising phase, Decay
64
To what mV does a typical undershoot reach?
-90 mV
65
To what mV does an AP rise?
+60 mV
66
T or F? K channels have an automated shut off mechanism whereas Na channels do not.
F. Vice versa
67
Why do K channels create an undershoot?
They linger open and don't have a shut off mechanism
68
Threshold is the voltage at which the sodium current becomes:
regenerative
69
What becomes regenerative at the threshold?
the Na current
70
What activates K channels?
depolarization
71
What does it mean that the AP is regenerative?
Na channels activate more Na channels
72
When does the Na current become regenerative?
when it exceeds the K current (is this always the same mV as the threshold?)/ overcome other voltages that might be working
73
What type of cycle controls the Na channels?
feedback cycle
74
What closes the Na channel at the RMP?
activation gate
75
What stops Na from flowing through the Na channel?
the inactivation gate
76
Where is the inactivation gate located?
intracellular side of the Na channel
77
Where is the activation gate located?
In the intramembraneous portion of the Na channel
78
Response of this segment allows for Na to rush in through the Na channels:
S4 segment
79
What does the S4 segment respond to?
change in voltage
80
How long does the Na channel typically remain open?
a couple ms's
81
How many "doors" does the Na channel have?
2, both must be open for Na to enter cell
82
This is the only way for the cell to recover:
to hyperpolarize, otherwise the channel is essentially useless bc that 2nd of the 2 gates is closed
83
What is the benefit of the inactivation gate?
helps to create rapid hyperpolarizaton (Na channels aren't fighting it)
84
T or F? Both the activation gate and the inactivation gate are closed in the resting state.
F. Activation gate is closed, inactivation gate is open
85
Is there a fast or slow recovery from inactivation?
slow
86
What is happening during the slow recovery from inactivation?
repolarization
87
Are both the activation gate and the inactivation gate closed during inactivation?
No, the activation gate is open
88
T or F? The inactivation gate can be closed even when depolarized.
T
89
When a channel is blocked which gate gets clogged?
Activation gate
90
T or F? Na and K channels both have activation gates and inactivation gates.
F. Na channels do, K channels only have activation gates
91
Voltage sensor:
S4
92
S4:
Voltage sensor
93
S5-6:
Activation gate
94
Activation gate:
S5-6
95
Channel pore:
P-loop
96
P-loop:
channel pore
97
What is the inactivation gate a part of?
the channel protein
98
How many domains does the voltage gated Na channel have?
4 (each with 6 transmembrane segments)
99
In which domain i the P-loop found?
Domain IV
100
How can the refractory period be tested?
by varying time bw 2 stimuli
101
T or F? Spike amplitude decreases with time during the relative refractory period.
F. increases
102
T or F? Both Na and K channels are close at the end of the absolute refractory period.
F. K are still open, Na are closed
103
T or F? The excitability of a neuron increase during the absolute refractory period.
F. remains at zero until the start of the relative refractory period
104
Does a decrease or increase in the K conductance cause hyperpolarization of the cell?
increase
105
T or F? As soon as all the Na channels have recovered fully another AP can easily be produced.
F. You would now have to depolarize more to produce a 2nd AP because the cell is hyperpolarized
106
What prevents back propagation of the AP?
ARP
107
In order for AP to propagate w/in a cell (+/-) charges flow into the adjacent sections of the axon by local current flow.
+, there is always a - charge on the opposite side of the PM
108
What repolarizes the membrane?
loss of L from the cytoplasm
109
What determines spike frequency?
relative refractory period
110
Excitability is linked to:
proportion of Na+ channels that can activate and not inactivated
111
What affects the spike threshold?
the rate of graded depolarization
112
What is the goal of the graded potential?
to allow enough positive charge to create a regenerative event
113
Are GP's more likely to produce an AP when they occur slowly, rapidly, or it doesn't make a difference.
rapidly
114
T or F? A quickly developing graded potential will have a higher AP threshold than a slow GP.
F. vice versa, slowly developing, quickly
115
T or F? A large GP will always produce an AP
F. If it is large and SLOW it will not bc many Na channels have inactivated during depolarization
116
Extracellular levels of __ are increased in hyperkalemia.
K
117
Is hyperkalemia related to intracellular K levels or extracellular K levels?
extra
118
Will the inside a the cell of a person who is hyperkalemic be more or less negative?
less negative (more positive)
119
Does hyperkalemia bring the membrane closer to or further from threshold?
closer to
120
Does hyperkalemia lead to a more likely or less likely AP?
more likely
121
T or F? Hyperkalemia hyperpolarizes the cell membrane.
F. Hypokalemia hyper polarizes the cell membrane
122
Does hypokalemia make the neuron more or less likely to fire an AP?
less
123
Does hypokalemia bring the membrane closer to or further from threshold?
further
124
Will the inside of a cell become more or less positive if the extracellular concentration of K raises?
more positive
125
Which makes the cell hyperexcitable, hyper or hypokalemia?
hyperkalemia
126
Intra and extracellular concentrations of K for a normal cell:
150 mM in, 5 mM out
127
2 drugs that can block voltage-gated Na channels:
tetrodoxin (TTX) and local anesthetics
128
How do local anesthetics block AP from forming?
block active Na and K channels or enhance Na channel inactivation
129
Do local anesthetics work better on small or large diameter fibers?
small
130
What does TTX stand for?
tetrodoxin
131
Lidocaine prevents recovery from:
the inactivated state and prevents the formation of APs
132
Describe pain conveying fibers:
small diameter, non- or lightly-myelinated
133
How many different subunits can voltage-gated Na channels be made of?
9
134
These subunits make of Na channels in the CNS:
Nav1.1, 1.2, 1.3, 1.6
135
These subunits make of Na channels in the PNS:
Nav1.1, 1.6, 1.7, 1.8, 1.9
136
These subunits make of Na channels in the skeletal muscle:
Nav1.4
137
These subunits make of Na channels in the cardiac muscle:
Nav1.5
138
How many genes express the subunits of the Na channels?
9
139
Pts with a mutation of this subunit of the Na channels can not sense pain:
Nav1.7 PNS
140
3 types of disorders resulting from mutation in Nav1.7:
Congenital insensitivity to pain (CIP), inherited erythromelalgia (IEM), paroxysmal extreme pain disorder (PEPD)
