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55 Cards in this Set

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