Term
| cell body is called the ______ |
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Definition
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Term
| sending arm of a neuronal signal is called the ______ |
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Definition
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Term
| action potentials are usually initiated at the _______ & travel down the axon to the synapse |
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Definition
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Term
| junction between two neurons is called the ______ |
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Definition
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Term
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Definition
| chemical released by a neuron that evokes a change in activity of another neuron |
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Term
| neuron's have a _______ for a membrane |
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Definition
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Term
| why do we care about water flowing across the membrane? |
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Definition
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Term
| why can sugar usually pass through the membrane? |
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Definition
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Term
| example of something else in the membrane besides just the phospholipids |
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Definition
| pores through which water can pass across the membrane |
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Term
| ion channels are ______ proteins |
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Definition
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Term
| a ______ membrane will allow molecule flow so that concentrations across the membrane are in equilibrium |
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Definition
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Term
| what would happen to KCl in water? |
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Definition
| dissolve into K+ & Cl- ions |
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Term
| electrochemical equilibrium is a balance considering what? |
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Definition
| balance considering both chemical & electrical forces on a charged ion species |
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Term
| symbol for electrochemical equilibrium |
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Definition
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Term
| electrochemical equilibrium |
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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 |
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Term
| electrochemical gradients |
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Definition
| a combination of the electrical & chemical gradients which determines the direction & magnitude of movement of ions across the membrane |
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Term
| what feature of ion channels is so important for electrochemical gradients? |
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Definition
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Term
| what equation allows you to calculate E for a given ion species? |
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Definition
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Term
| units for electrochemical equilibrium (E) |
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Definition
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Term
| a negative answer for electrochemical equilibrium (E) means that the "in" is _______ compared to the "out" |
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Definition
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Term
| 4 steps of how sodium-potassium ATPase works |
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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 |
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Term
| sodium potassium ATPase works as a ______ thing |
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Definition
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Term
| sodium-potassium ATPase is a very active process that is required to ______ |
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Definition
| maintain concentration gradients across the cell membrane |
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Term
| what happens if you change the voltage of the cell using electrical probe? |
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Definition
| system is not in equilibrium --> ions will want to move to make it equilibrium |
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Term
| ______ influences whether ions move in or out of the cell |
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Definition
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Term
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Definition
| the ability of a channel to let ions flow through |
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Term
| "Neuroscience version" of Ohm's Law |
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Definition
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Term
| If the voltage is being held at ______, there will be no driving force & current will be 0 |
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Definition
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Term
| "Equilibrium potential" is also called the ______ |
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Definition
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Term
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Definition
| graphical representation of Ohm's Law |
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Term
| X intercept of an IV plot tells you ______ |
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Definition
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Term
| slope of an IV plot = ______ |
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Definition
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Term
| changes in conductance will change what on an IV plot? |
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Definition
| slope of the line, but not the X-intercept |
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Term
| changes in reversal potential will change what on an IV plot? |
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Definition
| X-intercept, but not the slope |
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Term
| IV plot will always be ______ for a leak channel that is always open (i.e. potassium channel) |
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Definition
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Term
| [K+] is usually higher inside or outside of the cell? |
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Definition
| inside (because the sodium-potassium ATPase is constantly pumping potassium in) |
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Term
| [Na+] is usually higher inside or outside of the cell? |
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Definition
| outside (because the sodium-potassium ATPase is constantly pumping sodium out) |
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Term
| what equation do you use when calculating Vm when there are two different ion species that have differing reversal potentials? |
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Definition
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Term
| when cells are at rest, the resting membrane potential is usually close to the equilibrium potential for potassium (about -78.8 mV)...why? |
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Definition
| when the cell is at rest, the potassium leak channels are always open |
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Term
| does the sodium-potassium ATPase set the equilibrium potential? |
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Definition
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Term
| ______ channels allow action potentials to arise |
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Definition
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Term
| relative conductance of voltage-gated ion channels are much larger or much smaller than leak channels? |
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Definition
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Term
| instantaneous membrane potential of the cell is determined by ______ (2) |
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Definition
1. which ion channels are open
2. how much conductance they have relative to other channels |
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Term
| voltage-gated K channel is composed of ______ subunits |
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Definition
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Term
| 2 states of voltage-gated K channel |
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Definition
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Term
| does the voltage-gating of the sodium channel work by similar or different principles compared to voltage-gated K channel |
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Definition
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Term
| the "open" probability of a voltage-gated channel changes depending on ______ |
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Definition
| the membrane potential of a cell |
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Term
| 2 structural homologies between potassium & sodium voltage-gated channels |
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Definition
1. S4 transmembrane domain voltage sensor
2. S5-6 transmembrane domain selectivity filter |
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Term
| loop between domain III & IV in voltage gated sodium channel |
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Definition
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Term
| difference in structure between voltage-gated sodium channel & potassium version |
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Definition
| sodium is not four separate units...actually a continuous set-up with four domains |
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Term
| inactivation loop is relevant for the ______ channel |
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Definition
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Term
| how does the inactivation loop work? |
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Definition
| forms a "ball & chain" structure that swings into position to clog the pore of the channel |
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Term
| closed conformation of the sodium channel |
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Definition
| the voltage sensor is clamping the pore shut; the inactivation gate is just hanging off |
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Term
| open conformation of sodium channel |
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Definition
| happens when cell is depolarized enough for voltage sensor to shift & allow channel to open; ions can flow through |
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Term
| open inactivated conformation of sodium channel |
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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 |
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Term
| how much does intracellular sodium ion concentration change during an AP? |
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Definition
| the concentration of ions doesn't actually change very much! |
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Term
| action potential = a change in ______ |
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Definition
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Term
| graph the shape of an action potential on an axis of _______ vs _______ |
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Definition
| time (ms) vs voltage (mV) |
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Term
| resting membrane potential = ? |
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Definition
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Term
| initial phase of AP looks like _______ |
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Definition
| small creeping up of voltage |
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Term
| action potential threshold |
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Definition
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Term
| second phase of AP looks like ______ |
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Definition
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Term
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Definition
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Term
| third phase of AP looks like _______ |
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Definition
| membrane potential rapidly drops down |
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Term
| after-hyperpolarization phase (AHP) of AP |
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Definition
| drops even more hyperpolarized from resting membrane potential |
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Term
| what influences AP to rise gradually back up to resting membrane potential? |
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Definition
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Term
| 2 phases of refractory period |
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Definition
1. absolute refractory period (about 10 ms)
2. relative refractory period (about 10 - 50 ms) |
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Term
| refractory period is important for setting ______ |
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Definition
| the upper limit on firing rate |
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Term
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Definition
| the period of time following an action potential before a cell can fire again |
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Term
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Definition
| how many action potentials a neuron fires |
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Term
| firing rate of a neuron is discussed in terms of _______ |
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Definition
| Hz (number of events per second) |
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Term
| why would neurons have a maximum firing rate of 400-1,000 Hz? |
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Definition
| usually important for precision & accuracy |
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Term
| why would neurons have a maximum firing rate of only 20-50 Hz? |
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Definition
| usually important for integration of sensory input (need to integrate all of the information before firing downstream) |
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Term
| how do neurons meet the demands of the state they are in (what they want the maximum firing rate to be)? |
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Definition
| have different types of sodium or potassium channels |
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Term
| are there more genes for potassium or sodium channels? |
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Definition
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Term
| how would firing rate be influenced by having a super narrow AP (coming down from peak really fast)? |
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Definition
| capable of sustaining incredibly high firing rates |
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Term
| example of a type of neuron that has about the stereotypical shape |
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Definition
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Term
| potassium channel characteristics that would affect a neuron coming down from AP peak really slowly |
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Definition
| slow-acting kinetics (both on & off) |
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Term
| why is it important for normal cerebellar sodium channels to be really good at preventing inactivation? |
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Definition
| make sure they do not inactivate too early & are pretty much always ready to fire an action potential |
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Term
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Definition
| sodium channel gene that carries the mutation in ataxia patient |
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Term
| symptoms of ataxia (abnormal sodium channel inactivation) |
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Definition
| incredibly hard to walk & balance |
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Term
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Definition
| cell can't get hyperpolarized enough to de-inactivate the sodium channels |
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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 |
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Definition
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Term
| before hodgekin & huxley, it had been hypothesized that neurons were ______ cells |
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Definition
| electrical (electrical signals were required to get movement in the body) |
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Term
| hodgekin & huxley hypothesis |
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Definition
| action potential was a sudden increase in the permeability of the cell membrane to ions |
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Term
| size problem faced by hodgekin & huxley for AP studies |
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Definition
| axon diameter in CNS = 1 micron (human eyes can only see about 20 microns) |
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Term
| voltage clamp technology was invented during ______ |
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Definition
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Term
| hodgekin & huxley experiments got paused during ______ |
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Definition
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Term
| in voltage clamp, the ______ does not change |
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Definition
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Term
| what is the read-out of the voltage clamp? |
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Definition
| the amount of current that needs to be injected to hold the cell at a given potential |
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Term
| how fast are voltage steps in voltage clamp experiments? |
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Definition
| pretty much instantaneous |
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Term
| if you set holding potential to -85 mv --> ? |
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Definition
| basically no channels opening/closing for read-out to respond to --> graph looks like flat line |
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Term
| set holding potential to +26 --> ? |
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Definition
| initial inward current followed by outward current |
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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 |
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Term
|
Definition
TTX --> blocks voltage-gated sodium channels
TEA --> blocks voltage-gated potassium channels |
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Term
| when current is shown going downwards, it is an ______ current |
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Definition
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|
Term
| isolate Na+ current: use ______ |
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Definition
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Term
| isolate K+ current: use ______ |
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Definition
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Term
| what does it mean that channels are "binary" |
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Definition
| they are either opened or closed! |
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Term
| ______ current persists the entire time you keep the cell depolarized in voltage clamp |
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Definition
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Term
| ______ current does not persist the entire time you keep the cell depolarized in voltage clamp |
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Definition
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|
Term
| voltage-gated channel IV plots are generated by _______ |
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Definition
| clamp the cell at different holding potentials & look at how the amplitude of the current changes as a result |
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|
Term
| why does potassium channel current increase as voltage increases? |
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Definition
| there is a larger & larger difference between holding voltage & Ek |
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|
Term
| why are IV plots not linear? |
|
Definition
| conductance changes as a function of voltage! |
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|
Term
| How do you find Eion looking at an IV plot? |
|
Definition
| line starts moving off of x-axis at activation potential |
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|
Term
| why does voltage-gated sodium channel IV plot look linear for a certain amount of time? |
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Definition
| gmax reaches its constant |
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Term
| sodium channels activate at around _______ |
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Definition
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Term
| IV plot = ______ vs ______ |
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Definition
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Term
| current plot = ______ vs ______ |
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Definition
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Term
| ______ neurons are cell-autonomous bursting neurons |
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Definition
| TRN (thalamic reticular nucleus) |
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Term
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Definition
| really hyperpolarized & then shoot up & fire a bunch of APs but then after a little they stop (hyperpolarize again) & continue the process |
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Term
|
Definition
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|
Term
| what transitions a neuron from burst mode to firing mode? |
|
Definition
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Term
|
Definition
| top level; important for consciousness |
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|
Term
| where is the TRN located in the thalamus? |
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Definition
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|
Term
| where does the brain stem sit? |
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Definition
| in between spinal cord & main part of the brain |
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Term
| a huge amount of information passes in which direction through the thalamus? |
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Definition
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|
Term
| ______ during sleep --> entrain thalamus/cortex into rhythmic firing mode |
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Definition
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|
Term
| when you are awake, TRN neurons get inputs that transition them into _______ mode |
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Definition
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Term
|
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 |
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|
Term
| When you are awake: ACh is high or low? |
|
Definition
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|
Term
| When you are asleep: ACh is high or low? |
|
Definition
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|
Term
| when you are awake: histamine is high or low? |
|
Definition
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|
Term
| when you are asleep: histamine is high or low? |
|
Definition
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|
Term
| is ACh the only neurotransmitter involved in regulating levels in response to awake/asleep? |
|
Definition
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|
Term
| when you are giving no input to TRN, the default mode is _______ |
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Definition
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|
Term
| _______ sends sensory response information back down from the cortex |
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Definition
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|
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 |
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Term
|
Definition
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|
Term
|
Definition
| calcium-activate potassium channel |
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|
Term
| Ih channel turns off when cell is _______ & turns on when cell is _______ |
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Definition
| depolarized; hyperpolarized |
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|
Term
| how does Ih channel work in comparison to potassium current? |
|
Definition
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|
Term
| what happens to Ih current the more the cell hyperpolarizes below its voltage activation of -60 mv? |
|
Definition
|
|
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 |
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|
Term
| propagation of an action potential |
|
Definition
| depolarization of once section depolarizes the next one etc. which pushes it down the axon |
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|
Term
| action potential starts in ______ --> terminals |
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Definition
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|
Term
| if you wanted to speed up the action potential would you widen or shrink the axon? |
|
Definition
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|
Term
| length constant (lambda) can be discussed as ______ or ______ |
|
Definition
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|
Term
|
Definition
| the distance from max current flow until remaining current flow is 37% of the max |
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|
Term
| if action potential is going faster, does lambda increase or decrease? |
|
Definition
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|
Term
| if action potential slows does, does lambda increase or decrease? |
|
Definition
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|
Term
| myelin is a type of structure that is formed by specialized _______ cells |
|
Definition
|
|
Term
| is there still leak amongst the layers of myelin? |
|
Definition
| yes but it is just significantly less |
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|
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 |
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Definition
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|
Term
| in the CNS - myelin produced by _______ |
|
Definition
|
|
Term
| in the PNS - myelin produced by _____ |
|
Definition
|
|
Term
| myelin increases or decreases membrane resistance? |
|
Definition
| increases! --> increases lambda |
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|
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 |
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|
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 |
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|
Term
|
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
|
|
Term
| where does the name for "saltatory conduction" come from? |
|
Definition
|
|
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
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|
Term
| Charcot-Marie-Tooth (CMT) disease is a demyelination of the _______ |
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Definition
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