Process of Hyper-polarization to baseline in neuron AP

[Singhp03]

During the last half of the relative refractory period
shown in Figure 1, the membrane potential is
beginning to:

So I guessed they wanted to know what was happening in the RRP(relative refractory period) as the membrane potiential was going from hyperpolarized to base line(Em). My answer was depolarize following logic that since it overshot the resting potiential it would have to get rid of some of the charge. Instead the answer was repolarization, can any one tell me why it would be re-polarization instead of depolarization to get to the base line(resting potential) charge?
d repolarize.
B. hypelpolarize.
C. depolarize.
D. hypopolarize.

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[sciencebooks]

during the last half of the relative refractory period
shown in figure 1, the membrane potential is
beginning to:

so i guessed they wanted to know what was happening in the rrp(relative refractory period) as the membrane potiential was going from hyperpolarized to base line(em). My answer was depolarize following logic that since it overshot the resting potiential it would have to get rid of some of the charge. Instead the answer was repolarization, can any one tell me why it would be re-polarization instead of depolarization to get to the base line(resting potential) charge?
D repolarize.
B. Hypelpolarize.
C. Depolarize.
D. Hypopolarize.

---nvm

 

[shaboobly]

well if its hyperpolarized it has to become repolarized to the resting potential in order to receive another impluse (it doesnt have to go all the way to the resting potential, but it will cost more to depolarize it again for the impulse to get sent).

 

[member232]

Depolarization usually refers to positive movement from the baseline UP (not positive movement in general). When it "overshoots" as you've termed it, it is considered hyperpolarization because it is going negative to the baseline, but to recover from this overshoot, when the voltage goes from the value of -90 back to -70, it is offically called "repolarization"

 

[Singhp03]

Depolarization usually refers to positive movement from the baseline UP (not positive movement in general). When it "overshoots" as you've termed it, it is considered hyperpolarization because it is going negative to the baseline, but to recover from this overshoot, when the voltage goes from the value of -90 back to -70, it is offically called "repolarization"

got it thanks

 

[sciencebooks]

Depolarization usually refers to positive movement from the baseline UP (not positive movement in general). When it "overshoots" as you've termed it, it is considered hyperpolarization because it is going negative to the baseline, but to recover from this overshoot, when the voltage goes from the value of -90 back to -70, it is offically called "repolarization"

So is "repolarization" basically just any movement TOWARD the baseline?

 

[Sports Junky]

So is "repolarization" basically just any movement TOWARD the baseline?

A cell's standard potential is -70mV. This means there are more positive ions outside the cell in comparison to the inside.

When an stimulus depolarizes a cell past a threshold point (usually around 50mV), then the following events occur:
1) Depolarization - Voltage Gated Sodium Channels open allowing the cell to become more positive which increases potential (Sodium flows into cell)
2) Relative Refractory Period - Voltage Gated Sodium Channels are inactivated, so no matter how strong the stimulus, another Action Potential cannot occur.
3) Repolarization - Voltage Gated Potassium Channels open allowing the cell to become more negative which decreases potential (Potassium flows out of cell)
4) Hyperpolarization - The Voltage Gated Potassium Channels remain open for a substantial amount of time, and so lots of Potassium flows out. This leaves the cell with an even more negative potential than it started off with. This is called the Relative Refractory Period; another action potential might occur, but the stimulus has to be very strong in order to overcome the large negative potential of the cell. Remember, the cell has to reach -50mV in order to create an Action Potential, and its current potential may be around -80mV instead of -70mV at this point.

Over time, the sodium-potassium pump brings the membrane potential towards -70mV again. Since 2 potassium enter the cell, and 3 sodium leaves the cell, this pump actually works to increase membrane potential.

I hope this helps, membrane potentials are a key to the MCAT so I would understand all of the mechanisms well. Try and understand and map out the relevance of the following:
1) Leaky Potassium Channel
2) Voltage Gated Sodium Channel
3) Voltage Gated Potassium Channel

TL;DR - Depolarize always increases membrane potential (more positive), re-polarization/hyper polarization always decreases membrane potential (more negative)

 

[sciencebooks]

A cell's standard potential is -70mV. This means there are more positive ions outside the cell in comparison to the inside.

When an stimulus depolarizes a cell past a threshold point (usually around 50mV), then the following events occur:
1) Depolarization - Voltage Gated Sodium Channels open allowing the cell to become more positive which increases potential (Sodium flows into cell)
2) Relative Refractory Period - Voltage Gated Sodium Channels are inactivated, so no matter how strong the stimulus, another Action Potential cannot occur.
3) Repolarization - Voltage Gated Potassium Channels open allowing the cell to become more negative which decreases potential (Potassium flows out of cell)
4) Hyperpolarization - The Voltage Gated Potassium Channels remain open for a substantial amount of time, and so lots of Potassium flows out. This leaves the cell with an even more negative potential than it started off with. This is called the Relative Refractory Period; another action potential might occur, but the stimulus has to be very strong in order to overcome the large negative potential of the cell. Remember, the cell has to reach -50mV in order to create an Action Potential, and it may be around -80mV instead of -70mV at this point.

Over time, the sodium-potassium pump brings the membrane potential towards -70mV again. Since 2 potassium enter the cell, and 3 sodium leaves the cell, this pump actually works to increase membrane potential.

I hope this helps, membrane potentials are a key to the MCAT so I would understand all of the mechanisms well. Try and understand and map out the relevance of the following:
1) Leaky Potassium Channel
2) Voltage Gated Sodium Channel
3) Voltage Gated Potassium Channel

I understand these main concepts; it's just that the answer was "repolarization" even though the cell was technically becoming more positive in the case of the question/answer. Thank you though.

 

[Sports Junky]

I understand these main concepts; it's just that the answer was "repolarization" even though the cell was technically becoming more positive in the case of the question/answer. Thank you though.

Oh I jumped the gun I think... I didn't even properly read the question.

I would have followed your logic as well, I would have called it depolarization.

Now that I think about it, depolarization can only refer to starting an action potential. Re-polarization refers to restoring the membrane potential.

Sorry for the misunderstanding, I think I learned something as well

 

[Singhp03]

Oh I jumped the gun I think... I didn't even properly read the question.

I would have followed your logic as well, I would have called it depolarization.

Now that I think about it, depolarization can only refer to starting an action potential. Re-polarization refers to restoring the membrane potential.

Sorry for the misunderstanding, I think I learned something as well

From What I read tht about sums it up, its funny how such an easy generalization took so much effort to conclude lol why can't they say this in the books!

 

[sciencebooks]

From What I read tht about sums it up, its funny how such an easy generalization took so much effort to conclude lol why can't they say this in the books!

Agreed. I seriously pulled my books out of this one and nada, .