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Exam 1
Adv. Cellular Neuroscience
157
Other
Graduate
09/24/2019

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Term
cell body is called the ______
Definition
soma
Term
sending arm of a neuronal signal is called the ______
Definition
axon
Term
action potentials are usually initiated at the _______ & travel down the axon to the synapse
Definition
axon hillock
Term
junction between two neurons is called the ______
Definition
synapse
Term
neurotransmitter
Definition
chemical released by a neuron that evokes a change in activity of another neuron
Term
neuron's have a _______ for a membrane
Definition
lipid bilayer
Term
why do we care about water flowing across the membrane?
Definition
water contains ions
Term
why can sugar usually pass through the membrane?
Definition
it is neutral
Term
example of something else in the membrane besides just the phospholipids
Definition
pores through which water can pass across the membrane
Term
ion channels are ______ proteins
Definition
transmembrane
Term
a ______ membrane will allow molecule flow so that concentrations across the membrane are in equilibrium
Definition
passively permeable
Term
what would happen to KCl in water?
Definition
dissolve into K+ & Cl- ions
Term
electrochemical equilibrium is a balance considering what?
Definition
balance considering both chemical & electrical forces on a charged ion species
Term
symbol for electrochemical equilibrium
Definition
E
Term
electrochemical equilibrium
Definition
the electrical potential at which the flow of a particular ion into the cell is counterbalanced by the flow of ions outside the cell
Term
electrochemical gradients
Definition
a combination of the electrical & chemical gradients which determines the direction & magnitude of movement of ions across the membrane
Term
what feature of ion channels is so important for electrochemical gradients?
Definition
selective permeability
Term
what equation allows you to calculate E for a given ion species?
Definition
Nernst
Term
units for electrochemical equilibrium (E)
Definition
millivolts
Term
a negative answer for electrochemical equilibrium (E) means that the "in" is _______ compared to the "out"
Definition
hyperpolarized
Term
4 steps of how sodium-potassium ATPase works
Definition
1. cytoplasmic Na+ binds to the sodium-potassium pump
2. Na+ binding stimulates phosphorylation by ATP
3. phosphorylation causes the protein to change its conformation, expelling Na+ to the outside
4. extracellular K+ binds to the protein, triggering release of the phosphate group
5. loss of the phosphate restores the protein's original concentration
6. K+ is released & the Na+ sites are receptive again; the cycle repeats
Term
sodium potassium ATPase works as a ______ thing
Definition
cyclical
Term
sodium-potassium ATPase is a very active process that is required to ______
Definition
maintain concentration gradients across the cell membrane
Term
what happens if you change the voltage of the cell using electrical probe?
Definition
system is not in equilibrium --> ions will want to move to make it equilibrium
Term
______ influences whether ions move in or out of the cell
Definition
driving force
Term
conductance (g)
Definition
the ability of a channel to let ions flow through
Term
"Neuroscience version" of Ohm's Law
Definition
I = g(V - Eion)
Term
If the voltage is being held at ______, there will be no driving force & current will be 0
Definition
equilibrium potential
Term
"Equilibrium potential" is also called the ______
Definition
"reversal potential"
Term
IV plots
Definition
graphical representation of Ohm's Law
Term
X intercept of an IV plot tells you ______
Definition
the reversal potential
Term
slope of an IV plot = ______
Definition
conductance
Term
changes in conductance will change what on an IV plot?
Definition
slope of the line, but not the X-intercept
Term
changes in reversal potential will change what on an IV plot?
Definition
X-intercept, but not the slope
Term
IV plot will always be ______ for a leak channel that is always open (i.e. potassium channel)
Definition
linear
Term
[K+] is usually higher inside or outside of the cell?
Definition
inside (because the sodium-potassium ATPase is constantly pumping potassium in)
Term
[Na+] is usually higher inside or outside of the cell?
Definition
outside (because the sodium-potassium ATPase is constantly pumping sodium out)
Term
what equation do you use when calculating Vm when there are two different ion species that have differing reversal potentials?
Definition
goldman-hodgkin-katz
Term
when cells are at rest, the resting membrane potential is usually close to the equilibrium potential for potassium (about -78.8 mV)...why?
Definition
when the cell is at rest, the potassium leak channels are always open
Term
does the sodium-potassium ATPase set the equilibrium potential?
Definition
no!
Term
______ channels allow action potentials to arise
Definition
voltage-gated ion
Term
relative conductance of voltage-gated ion channels are much larger or much smaller than leak channels?
Definition
larger
Term
instantaneous membrane potential of the cell is determined by ______ (2)
Definition
1. which ion channels are open
2. how much conductance they have relative to other channels
Term
voltage-gated K channel is composed of ______ subunits
Definition
4 (tetramer)
Term
2 states of voltage-gated K channel
Definition
1. open
2. closed
Term
does the voltage-gating of the sodium channel work by similar or different principles compared to voltage-gated K channel
Definition
primarily the same
Term
the "open" probability of a voltage-gated channel changes depending on ______
Definition
the membrane potential of a cell
Term
2 structural homologies between potassium & sodium voltage-gated channels
Definition
1. S4 transmembrane domain voltage sensor
2. S5-6 transmembrane domain selectivity filter
Term
loop between domain III & IV in voltage gated sodium channel
Definition
inactivation loop
Term
difference in structure between voltage-gated sodium channel & potassium version
Definition
sodium is not four separate units...actually a continuous set-up with four domains
Term
inactivation loop is relevant for the ______ channel
Definition
voltage-gated sodium
Term
how does the inactivation loop work?
Definition
forms a "ball & chain" structure that swings into position to clog the pore of the channel
Term
closed conformation of the sodium channel
Definition
the voltage sensor is clamping the pore shut; the inactivation gate is just hanging off
Term
open conformation of sodium channel
Definition
happens when cell is depolarized enough for voltage sensor to shift & allow channel to open; ions can flow through
Term
open inactivated conformation of sodium channel
Definition
within a couple milliseconds, the inactivation gate swings in & clogs up the pore; the channel is still open but no current is flowing because it is inactive
Term
how much does intracellular sodium ion concentration change during an AP?
Definition
the concentration of ions doesn't actually change very much!
Term
action potential = a change in ______
Definition
voltage
Term
graph the shape of an action potential on an axis of _______ vs _______
Definition
time (ms) vs voltage (mV)
Term
resting membrane potential = ?
Definition
about -70 mV
Term
initial phase of AP looks like _______
Definition
small creeping up of voltage
Term
action potential threshold
Definition
around -50 mV
Term
second phase of AP looks like ______
Definition
huge rise in voltage
Term
AP peak
Definition
around 30 mV
Term
third phase of AP looks like _______
Definition
membrane potential rapidly drops down
Term
after-hyperpolarization phase (AHP) of AP
Definition
drops even more hyperpolarized from resting membrane potential
Term
what influences AP to rise gradually back up to resting membrane potential?
Definition
leak channels
Term
2 phases of refractory period
Definition
1. absolute refractory period (about 10 ms)
2. relative refractory period (about 10 - 50 ms)
Term
refractory period is important for setting ______
Definition
the upper limit on firing rate
Term
refractory period
Definition
the period of time following an action potential before a cell can fire again
Term
firing rate of a neuron
Definition
how many action potentials a neuron fires
Term
firing rate of a neuron is discussed in terms of _______
Definition
Hz (number of events per second)
Term
why would neurons have a maximum firing rate of 400-1,000 Hz?
Definition
usually important for precision & accuracy
Term
why would neurons have a maximum firing rate of only 20-50 Hz?
Definition
usually important for integration of sensory input (need to integrate all of the information before firing downstream)
Term
how do neurons meet the demands of the state they are in (what they want the maximum firing rate to be)?
Definition
have different types of sodium or potassium channels
Term
are there more genes for potassium or sodium channels?
Definition
voltage-gated potassium
Term
how would firing rate be influenced by having a super narrow AP (coming down from peak really fast)?
Definition
capable of sustaining incredibly high firing rates
Term
example of a type of neuron that has about the stereotypical shape
Definition
CA1 pyramidal neurons
Term
potassium channel characteristics that would affect a neuron coming down from AP peak really slowly
Definition
slow-acting kinetics (both on & off)
Term
why is it important for normal cerebellar sodium channels to be really good at preventing inactivation?
Definition
make sure they do not inactivate too early & are pretty much always ready to fire an action potential
Term
Scn8a
Definition
sodium channel gene that carries the mutation in ataxia patient
Term
symptoms of ataxia (abnormal sodium channel inactivation)
Definition
incredibly hard to walk & balance
Term
depolarization block
Definition
cell can't get hyperpolarized enough to de-inactivate the sodium channels
Term
______ technique allowed us to learn that the upsweep of an action potential is due to sodium ions & down sweep of action potential is due to potassium ions
Definition
voltage clamp
Term
before hodgekin & huxley, it had been hypothesized that neurons were ______ cells
Definition
electrical (electrical signals were required to get movement in the body)
Term
hodgekin & huxley hypothesis
Definition
action potential was a sudden increase in the permeability of the cell membrane to ions
Term
size problem faced by hodgekin & huxley for AP studies
Definition
axon diameter in CNS = 1 micron (human eyes can only see about 20 microns)
Term
voltage clamp technology was invented during ______
Definition
WWII
Term
hodgekin & huxley experiments got paused during ______
Definition
WWII
Term
in voltage clamp, the ______ does not change
Definition
voltage
Term
what is the read-out of the voltage clamp?
Definition
the amount of current that needs to be injected to hold the cell at a given potential
Term
how fast are voltage steps in voltage clamp experiments?
Definition
pretty much instantaneous
Term
if you set holding potential to -85 mv --> ?
Definition
basically no channels opening/closing for read-out to respond to --> graph looks like flat line
Term
set holding potential to +26 --> ?
Definition
initial inward current followed by outward current
Term
how to isolate individual currents in voltage clamp (without pharmacology)
Definition
change concentration of sodium or potassium in outside solution --> changes reversal potential of that ion
Term
TTX vs TEA
Definition
TTX --> blocks voltage-gated sodium channels

TEA --> blocks voltage-gated potassium channels
Term
when current is shown going downwards, it is an ______ current
Definition
inward
Term
isolate Na+ current: use ______
Definition
TEA
Term
isolate K+ current: use ______
Definition
TTX
Term
what does it mean that channels are "binary"
Definition
they are either opened or closed!
Term
______ current persists the entire time you keep the cell depolarized in voltage clamp
Definition
potassium
Term
______ current does not persist the entire time you keep the cell depolarized in voltage clamp
Definition
sodium
Term
voltage-gated channel IV plots are generated by _______
Definition
clamp the cell at different holding potentials & look at how the amplitude of the current changes as a result
Term
why does potassium channel current increase as voltage increases?
Definition
there is a larger & larger difference between holding voltage & Ek
Term
why are IV plots not linear?
Definition
conductance changes as a function of voltage!
Term
How do you find Eion looking at an IV plot?
Definition
line starts moving off of x-axis at activation potential
Term
why does voltage-gated sodium channel IV plot look linear for a certain amount of time?
Definition
gmax reaches its constant
Term
sodium channels activate at around _______
Definition
-55 mV
Term
IV plot = ______ vs ______
Definition
voltage vs current
Term
current plot = ______ vs ______
Definition
time vs current
Term
______ neurons are cell-autonomous bursting neurons
Definition
TRN (thalamic reticular nucleus)
Term
burst mode
Definition
really hyperpolarized & then shoot up & fire a bunch of APs but then after a little they stop (hyperpolarize again) & continue the process
Term
tonic firing mode
Definition
consistently firing APs
Term
what transitions a neuron from burst mode to firing mode?
Definition
a stimulus
Term
cortex
Definition
top level; important for consciousness
Term
where is the TRN located in the thalamus?
Definition
kind of wraps around it
Term
where does the brain stem sit?
Definition
in between spinal cord & main part of the brain
Term
a huge amount of information passes in which direction through the thalamus?
Definition
both directions
Term
______ during sleep --> entrain thalamus/cortex into rhythmic firing mode
Definition
burst mode
Term
when you are awake, TRN neurons get inputs that transition them into _______ mode
Definition
tonic firing
Term
tonic state
Definition
cell is receiving some sort of depolarizing input to where its resting potential gets just hyperpolarized enough to de-inactivate sodium channels but then it is depolarized enough to spike right back up
Term
When you are awake: ACh is high or low?
Definition
high
Term
When you are asleep: ACh is high or low?
Definition
low
Term
when you are awake: histamine is high or low?
Definition
low
Term
when you are asleep: histamine is high or low?
Definition
high
Term
is ACh the only neurotransmitter involved in regulating levels in response to awake/asleep?
Definition
no
Term
when you are giving no input to TRN, the default mode is _______
Definition
bursting
Term
_______ sends sensory response information back down from the cortex
Definition
thalamus
Term
5 things you need to build a cell-autonomous bursting neuron
Definition
1. voltage-gated Na+
2. voltage-gated K+
3. 2 types of Ca2+ channels --> depolarize a neuron
4. Ca2+-activated K+ channels
5. Ih = mixed cation channel that opens at hyperpolarized voltages
Term
SK stands for
Definition
"small conductance"
Term
SK is a type of ______
Definition
calcium-activate potassium channel
Term
Ih channel turns off when cell is _______ & turns on when cell is _______
Definition
depolarized; hyperpolarized
Term
how does Ih channel work in comparison to potassium current?
Definition
opposite
Term
what happens to Ih current the more the cell hyperpolarizes below its voltage activation of -60 mv?
Definition
gets bigger
Term
what does it mean that action potentials are all or nothing?
Definition
once you reach your threshold, you are going to get an AP
Term
propagation of an action potential
Definition
depolarization of once section depolarizes the next one etc. which pushes it down the axon
Term
action potential starts in ______ --> terminals
Definition
axon hillock (near soma)
Term
if you wanted to speed up the action potential would you widen or shrink the axon?
Definition
widen the axon
Term
length constant (lambda) can be discussed as ______ or ______
Definition
distance or time
Term
length constant (lambda)
Definition
the distance from max current flow until remaining current flow is 37% of the max
Term
if action potential is going faster, does lambda increase or decrease?
Definition
increase
Term
if action potential slows does, does lambda increase or decrease?
Definition
decrease
Term
myelin is a type of structure that is formed by specialized _______ cells
Definition
glial
Term
is there still leak amongst the layers of myelin?
Definition
yes but it is just significantly less
Term
you can think of ______ as insulating the entire neuron with an entirely separate family of cells whose sole purpose is to help the neuron transmit signals faster
Definition
myelin
Term
in the CNS - myelin produced by _______
Definition
oligodendrocytes
Term
in the PNS - myelin produced by _____
Definition
Schwann cells
Term
myelin increases or decreases membrane resistance?
Definition
increases! --> increases lambda
Term
how does myelin affect charges inside vs outside of the neuron?
Definition
literally increases the distance between these charges
Term
why does it help that myelin increases the distance between charges inside & outside of the neuron?
Definition
depolarizing the cell is kicking out the negative charges, so the harder it is to do this the harder it is to depolarize
Term
what does it mean that myelin is not perfect?
Definition
there is still some leak --> there is still some attenuation moving down the axon
Term
nodes of Ranvier
Definition
gaps in myelin down the axon (you need sodium channels along the way to re-charge the action potential signal!)
Term
why are there gaps in between the myelination along the axon?
Definition
AP still decays --> we need our ion channels accessible
Term
is ion channel density high or low at nodes of Ranvier?
Definition
high
Term
where does the name for "saltatory conduction" come from?
Definition
Latin word for "jump"
Term
how does myelin allow for the need of fewer ATPases?
Definition
cluster of ion channels means that where the gradient needs to be maintained is limited to where these clusters are
Term
multiple sclerosis is a _______ autoimmune disorder
Definition
CNS
Term
Charcot-Marie-Tooth (CMT) disease is a demyelination of the _______
Definition
PNS
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