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55 Cards in this Set
- Front
- Back
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Why can't Na+ go through K+ channels?
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Because Na+ has water around it and thus it's too large
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Which NT allows Na+ and K+ to diffuse?
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ACh
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Which NT allows Cl- to diffuse?
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GABA
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What are the two forces that affect ion diffusion?
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Concentration (chemical gradient and electrical gradient
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What is membrane potential?
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Membrane potential is the separation of charge across the membrane
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At rest, what is the membrane potential, Vm?
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Vm = -70 mV
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What is the electrical gradient?
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Electrical gradient is when cations move toward negative charge or anions move toward positive charge.
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Ions are attracted toward areas of what?
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Opposite charge
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When cations go toward negative charge and anions go toward positive charge, what is this called?
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Moving down (along) the electrical gradient
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The actual movement of ions is due to what?
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A combination of both forces: Electrochemical gradient
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The inside the neuron is more positive or negative?
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Negative
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An ion diffuses due to the what, regarding it's gradient?
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Due to the sum of its concentration and electrical gradients
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With passive diffusion, an ion will move up or down its concentration gradient?
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DOWN!
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TRUE OR FALSE: It is possible for an ion to move toward an area of same charge (against its electrical gradient).
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True only if concentration gradient exceeds the electrical gradient
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Which direction does Na+ diffuse when crossing the membrane?
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Into the cell
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Is Na+ diffusing down or up its concentration gradient?
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Down
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Is Na+ diffusing down or up its electrical gradient?
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Down
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Which direction does K+ diffuse when crossing the cell membrane?
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Out of the cell
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Is K+ diffusing down or up its concentration gradient?
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Down
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Is K+ diffusing down or up its electrical gradient?
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Up
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If the inside negative charge becomes too great, what may happen to K+?
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K+ may be kept from leaving
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What cells have Vm?
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ALL cells
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Where does charge separation exist?
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ONLY at the membrane
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At rest, which channels are open?
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Leak channels
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At rest, which channels are closed?
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Gated channels
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What are the 5 factors contributing to resting Vm?
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1. Unequal ion distribution
2. More leak channels for K+ than for Na+ 3. A- trapped inside 4. K+ diffuses out; leaves A- behind 5. Some Na+ leaks in; doesn't match K+ efflux |
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What happens to the K+ and Na+ gradients if there's no pump?
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Gradients will run down. Na+ and K+ concentrations will become the same inside and outside
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What are 2 ways Vm can change in a graded potential?
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Depolarization and hyperpolarization
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What is depolarization?
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Depolarization is where Vm becomes more positive than -70 mV
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What causes depolarization?
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Na+ diffuses in
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What is threshold? What occurs at threshold?
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Threshold is -55 mV. At this point, neuron is more likely to fire APs
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What is hyperpolarization?
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Hyperpolarization is when Vm becomes more negative than -70 mV
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What causes hyperpolarization?
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K+ diffusing out and Cl- diffusing in
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What does hyperpolarization cause?
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It inhibits the neuron and makes it less likely an AP will fire.
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Why is inhibition of AP important?
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To stop movement quickly
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If a graded potential is strong enough to depolarize to -55 mV at the trigger zone, what occurs?
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AP will fire
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What happens when graded depolarization arrives at trigger zone?
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It begins to open voltage-gated Na+ channels and if enough open, it triggers APs
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AP is what kind of event?
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An All or None event
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What must depolarize to -55 mV to set off?
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AP
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Do AP die out or are they regenerative?
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Regenerative
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How do APs regenerate?
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Propagate by opening other voltage-gated channels all the way down the axon
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Which channels open quickly?
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Na+ Channels
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Which channels open slowly?
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K+ Channels
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At resting state, which channels are open? Which channels are closed?
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Leak channels are open and Na+ and K+ channels are closed.
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During depolarization, which channels are open and which channels are closed?
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Na+ channels are open and K+ channels are closed.
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Depolarization opens more Na+ channels. This is what kind of feedback?
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Positive feedback!
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At threshold, all Na+ channels have what?
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Opened
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What is the voltage of the peak?
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+30 mV
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During repolarization, which channels are open and which channels are closed?
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K+ channels open and Na+ channels close and lock
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When Vm return to resting value, what happens to the Na+ channels?
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Na+ channels go back to closed but ready to open
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During hyperpolarization, which channels are open and which channels are closed?
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TRICK QUESTION! K+ channels are open but are starting to close and Na+ channels are closed and ready to open.
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Why is hyperpolarization during an AP not the same as hyperpolarization in a graded potential?
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AP hyperpolarization is because voltage-gated channels slowly close and K+ is still leaving. GP hyperpolarization occurs when chemical-gated channels open and either K+ leaves or Cl- enters
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Hypothetically, an AP could occur by having only voltage-gated Na+ channels and a Na+ pump. Na+ could diffuse in to depolarize and then Na+ could be pumped out to repolarize. What are the disadvantages of firing APs in this way?'
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Uses more ATP and is too slow
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TRUE OR FALSE: In firing a single AP, large amounts of Na+ and K+ cross the membrane.
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FALSE. Few ions actually cross
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TRUE OR FALSE: The Na+/K+ pump MUST run to be able to fire a second AP.
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FALSE, because so few ions go through Na+/K+ pumps can be turned off and neuron can still fire 100K APs.
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