Q___________action potential/RMP===============q38 - miracoli

[ArchivalUser]

A woman with severe muscle weakness is hospitalized. The only abnormality in her lab values is an elevated serum potassium concentration.The elevated serum K causes muscle weakness because
A) The resting membrane potential is hyperpolarized
B) The K equilibrium potential is hyperpolarized
C) The Na equilibrium potential is hyperpolarized
D) K channels are closed by depolarization
E) K channels are opened by depolarization
F) Na channels are closed by depolarization
G) Na channels are opened by depolarization

[ArchivalUser]

AA
I think that resting membrane potential is because of concentration dependent k+ channels. If extracellular potassium is high than this conc gradient will be lost and hence there will be effect on rmp.
Please correct me if I am thinking wrong.

I will read physio today and try to re read all your Qs.
Having these Qs in mind makes reading so interesting.
Thanks for posting the Qs It helps a lot.

[ArchivalUser]

AA is wrong. I am sorry.
RMP wont be hyperpolarized instead it will depolarise quickly.

I cannot figure out if its FF or EE?

Here's my reason

Potassium channels are concentration dependent.
Increase extracellular conc of K+ ----> Influx of potassium ( Rather than Efflux)
Hence depolarization. [option 1 ruled out]

Depolarization due to concentration change is slow, it never generates an action potential by itself instead, it results in accommodation. Above a certain level of potassium the depolarization inactivates sodium channels, opens potassium channels, thus the cells become refractory.
( from Wikipedia )
Please ignore if you are looking for a correct explanation.
I am just discussing. And I dont know if this is a correct reasoning.
Thanks

[ArchivalUser]

@medicus, can you try and explain this one?

[ArchivalUser]

FFFF

because there is more Extracellular K, won't efflux out down concentration gradient . so Na channels will stay closed

I think that is what choice FF means

[ArchivalUser]

@ Miracoli ....Thank u so much .....Amazing q ....so helpful

[ArchivalUser]

F is correct

Elevated seum K concentration will decrease the concentration gradient for K--> less negative K equilibrium potential--> more K ions stay inside the cell--> depolarization of the RMP in skeletal muscle--> Sustained depolarization closes the inactivation gates of Na channels--> inactive Na channels--> this prevents the occurence of action potentials in the muscle--> muscle weakness

go@usmle1, you are welcome


more info is here
http://www.usmleforum.com/showthread.php?tid=767949