TBR 1 Question

[Joker88]

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There was a question that asked which part in the production of an action potential would prevent tetanization. The answer was absolute refractory period but I'm not sure how. I thought absolute refractory included the actual depolarization part of the action potential production so how could the cell be given rest to prevent a continuous muscle spasm? I thought it was more likely to be Relative Refractory period. help please!

 

[salim271]

There was a question that asked which part in the production of an action potential would prevent tetanization. The answer was absolute refractory period but I'm not sure how. I thought absolute refractory included the actual depolarization part of the action potential production so how could the cell be given rest to prevent a continuous muscle spasm? I thought it was more likely to be Relative Refractory period. help please!

Ah i remember that one. Continuous muscle spasm ---> means that there is a continuous/repeated depolarization. The absolute refractory period means that no depolarization can happen, only repolarization. Thus you cannot have a continuous muscle spasm. The relative refractory period is a time when depolarization can happen again.

What defines the absolute and relative periods are the types of gates that are open at the time. That... is something I have forgotten 🙁. I believe in absolute, Voltage Gated K channels are open and cannot be closed, VG Na channels are closed and cannot be opened. In Relative refractory period, I believe VGK channels are closed or closing, and VG Na channels can be closed, or open, depending if there is another action potential fired. Check a book though, I'm pulling that from memory and logicking.

 

[gunj122]

almost got it. Absolute covers the majority of the AP, including the depolarization and repolarization phases. The relative covers the hyperpolarization phase.

During the absolute, the Na channels have an inactivation gate on the cytosol side which prevents any ion flow, regardless if the channel is in the open conformation. once the cell becomes hyperpolarized, aka cell potential falls below rest potential, the inactivation gate is opened and the Na channels are able to conduct once again. now this point we are in the relative refractory period, where K channels are open and K ions are flooding out of the cell. this is when it takes a much greater change in voltage to initiate the AP. this makes sense considering the cell is hyperpolarized and further away from threshold. the refractory periods end when the cell returns to resting potential.

I believe in absolute, Voltage Gated K channels are open and cannot be closed, VG Na channels are closed and cannot be opened. In Relative refractory period, I believe VGK channels are closed or closing, and VG Na channels can be closed, or open, depending if there is another action potential fired. Check a book though, I'm pulling that from memory and logicking.

 

[salim271]

almost got it. Absolute covers the majority of the AP, including the depolarization and repolarization phases. The relative covers the hyperpolarization phase.

XD Yeah thats the story of my life, i need to use that as my sig...