Lecture 3 Flashcards
Speed of depolarization:
about 1ms 1/1000th of a sec
Speed of AP:
about 200 mph
How many voltage gated channels are involved in the formation of APs?
2 Na (depolarize) and K (repolarize)
What causes the termination of the AP?
Opening of the K channels
T or F? APs are analog signals.
F. digital. Its there or it’s not
This type of signal can very over an enormous range:
graded analog
What produces the absolute and relative refractory periods?
recovery oft he Na and K channels
T or F? It is possible to produce another AP during the relative refractory period.
T. Just requires a stronger stimulus
What type of potentials are produces at the synapse?
graded
T or F? Graded potentials can summate.
T
T or F? APs can summate.
F
This segment of the neuron has a very high concentration of sodium channels
trigger zone (initial segment)
This type of potential is good at starting to produce a response that you can finely tune:
graded
This type of potential can be used to compute things
graded
T or F. Graded potentials (GP’s) do not diminish with distance.
F. They do diminish with distance
What happens in GPs are above the threshold in the Trigger Zone?
they produce spikes
Does a graded potential start below or above threshold?
Above
Is a GP above or below the threshold at the trigger zone?
It depends on the initial strength of the stimulus.
Will the release of Glu depolarize or depolarize a cell?
depolarize
T or F? Na channels can be found all over the neuron.
F. localized in the trigger zone
Why is there less positive charge as you get closer to the trigger zone with a graded potential?
Na leaks out and the inside will be less positive
T or F? A weak stimulus will release little neurotransmitter and a strong stimulus will release more.
T
Are APs generated along efferent or afferent neurons?
Afferent
What is AP frequency proportional to?
Graded potential amplitude
What happens if the graded potential is just at threshold?
it will on ly produce a few APs
Can EPSPs (Excitatory post-synatic potential) produce APs?
Yes, if they are large enough
The strength of a stimulus is encoded in:
the graded potential
T or F? The bigger the graded potential, the higher the frequency.
T
A strong, graded potential will produce:
many APs at a high frequency
How can the frequency of APs be increased?
increase the strength of the graded potential
The size of the graded potential is proportional to:
the number of activated channels
T or F? Graded potentials can be both positive and negative
T. EPSP or IPSP
T or F? Naps have variable amplitude
F. Graded potentials do
Are graded potentials at the synapse fast or slow?
slow
Are APs at axon initial segment slow or fast?
fast
T or F? Graded potentials at synapse have a stereotyped response.
F. APs do
The polarity of this type of potential can vary:
graded potential
What encodes the strength of the stimulus in neurons?
spike frequency and EPSP amplitude of the synaptic current
Both of these will be lower with a mall graded potential in comparison to a large graded potential:
amplitude and spike frequency
T or F? The inside of the cell becomes more positive with an IPSP.
F. More negative
What type of signal does a graded potential get in a neuron?
input signal
What type of signal does a AP get in a neuron?
conduction signal
Where does a GP typically occur in a neuron?
dendrites and cell bodies
Where does an AP typically occur in a neuron?
trigger zone through an axon
What type(s) of gated ion channel are involved with graded potentials?
mechanically, chemically, or voltage-gated channels
What type(s) of gated ion channel are involved with APs?
Voltage-gated only
What ions are involved with GPs?
usually Na, Cl, and Ca
What ions are involved with APs?
Na and K
Does a graded potential (lead to?) a signal that is depolarizing or hyperpolarizing?
either
Does an AP (lead to?) a signal that is depolarizing or hyperpolarizing?
depolarizing
What does the strength of the signal of the GP depend upon?
initial stimulus, can be summed
What does the strength of the signal of the AP depend upon?
it is always the same (all-or-none), cannot be summed
What initiates the signal for a GP?
entry of ions through channels
What initiates the signal for a AP?
Above-threshold GP at the trigger zone
T or F? There is a minimum level required to initiate a GP/
F.
What is the initial stimulus strength indicated by for a GP?
frequency of a series of APs
T or F? All cell at rest will have no open channels.
F. some are open (leak channels), we don’t know which
3 types of channels leading to an AP:
- Unregulated (leak) channels produce the resting membrane potential
- Synaptic, ligand-gated channels produce graded potential
- Voltage gated channels produce the AP
What type of channel produces the resting membrane potential?
Unregulated, leak channels
What type of channel produces the graded potential?
Synaptic, ligand-gated channels
What type of channel produces the AP?
Voltage gated channel
What channels cause the undershoot?
K channels
What are the names of the two sides of the spike of an AP called?
Rising phase, Decay
To what mV does a typical undershoot reach?
-90 mV
To what mV does an AP rise?
+60 mV
T or F? K channels have an automated shut off mechanism whereas Na channels do not.
F. Vice versa
Why do K channels create an undershoot?
They linger open and don’t have a shut off mechanism
Threshold is the voltage at which the sodium current becomes:
regenerative
What becomes regenerative at the threshold?
the Na current
What activates K channels?
depolarization
What does it mean that the AP is regenerative?
Na channels activate more Na channels
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
What type of cycle controls the Na channels?
feedback cycle
What closes the Na channel at the RMP?
activation gate
What stops Na from flowing through the Na channel?
the inactivation gate
Where is the inactivation gate located?
intracellular side of the Na channel
Where is the activation gate located?
In the intramembraneous portion of the Na channel
Response of this segment allows for Na to rush in through the Na channels:
S4 segment
What does the S4 segment respond to?
change in voltage
How long does the Na channel typically remain open?
a couple ms’s
How many “doors” does the Na channel have?
2, both must be open for Na to enter cell
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
What is the benefit of the inactivation gate?
helps to create rapid hyperpolarizaton (Na channels aren’t fighting it)
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
Is there a fast or slow recovery from inactivation?
slow
What is happening during the slow recovery from inactivation?
repolarization
Are both the activation gate and the inactivation gate closed during inactivation?
No, the activation gate is open
T or F? The inactivation gate can be closed even when depolarized.
T
When a channel is blocked which gate gets clogged?
Activation gate
T or F? Na and K channels both have activation gates and inactivation gates.
F. Na channels do, K channels only have activation gates
Voltage sensor:
S4
S4:
Voltage sensor
S5-6:
Activation gate
Activation gate:
S5-6
Channel pore:
P-loop
P-loop:
channel pore
What is the inactivation gate a part of?
the channel protein
How many domains does the voltage gated Na channel have?
4 (each with 6 transmembrane segments)
In which domain i the P-loop found?
Domain IV
How can the refractory period be tested?
by varying time bw 2 stimuli
T or F? Spike amplitude decreases with time during the relative refractory period.
F. increases
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
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
Does a decrease or increase in the K conductance cause hyperpolarization of the cell?
increase
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
What prevents back propagation of the AP?
ARP
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
What repolarizes the membrane?
loss of L from the cytoplasm
What determines spike frequency?
relative refractory period
Excitability is linked to:
proportion of Na+ channels that can activate and not inactivated
What affects the spike threshold?
the rate of graded depolarization
What is the goal of the graded potential?
to allow enough positive charge to create a regenerative event
Are GP’s more likely to produce an AP when they occur slowly, rapidly, or it doesn’t make a difference.
rapidly
T or F? A quickly developing graded potential will have a higher AP threshold than a slow GP.
F. vice versa, slowly developing, quickly
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
Extracellular levels of __ are increased in hyperkalemia.
K
Is hyperkalemia related to intracellular K levels or extracellular K levels?
extra
Will the inside a the cell of a person who is hyperkalemic be more or less negative?
less negative (more positive)
Does hyperkalemia bring the membrane closer to or further from threshold?
closer to
Does hyperkalemia lead to a more likely or less likely AP?
more likely
T or F? Hyperkalemia hyperpolarizes the cell membrane.
F. Hypokalemia hyper polarizes the cell membrane
Does hypokalemia make the neuron more or less likely to fire an AP?
less
Does hypokalemia bring the membrane closer to or further from threshold?
further
Will the inside of a cell become more or less positive if the extracellular concentration of K raises?
more positive
Which makes the cell hyperexcitable, hyper or hypokalemia?
hyperkalemia
Intra and extracellular concentrations of K for a normal cell:
150 mM in, 5 mM out
2 drugs that can block voltage-gated Na channels:
tetrodoxin (TTX) and local anesthetics
How do local anesthetics block AP from forming?
block active Na and K channels or enhance Na channel inactivation
Do local anesthetics work better on small or large diameter fibers?
small
What does TTX stand for?
tetrodoxin
Lidocaine prevents recovery from:
the inactivated state and prevents the formation of APs
Describe pain conveying fibers:
small diameter, non- or lightly-myelinated
How many different subunits can voltage-gated Na channels be made of?
9
These subunits make of Na channels in the CNS:
Nav1.1, 1.2, 1.3, 1.6
These subunits make of Na channels in the PNS:
Nav1.1, 1.6, 1.7, 1.8, 1.9
These subunits make of Na channels in the skeletal muscle:
Nav1.4
These subunits make of Na channels in the cardiac muscle:
Nav1.5
How many genes express the subunits of the Na channels?
9
Pts with a mutation of this subunit of the Na channels can not sense pain:
Nav1.7 PNS
3 types of disorders resulting from mutation in Nav1.7:
Congenital insensitivity to pain (CIP), inherited erythromelalgia (IEM), paroxysmal extreme pain disorder (PEPD)
