question about membrane potential

[wuwu thedentist]

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I got this from usmle and I just cannot understand this!

increase of extracellular sodium or potassium causes the cell to tend to depolarize..and vis versa... but why?

it seems like it should be the opposite to me.

if there is an increased cation outside the cell membrane, doesn't that make the outside more positive, and relatively doesn't the cell have to be hyperpolarized?
I don't know what I'm missing...
I'll really appreciate it if someone helps me with this...
thanks a lot!

 

[missiondds]

I got this from usmle and I just cannot understand this!

increase of extracellular sodium or potassium causes the cell to tend to depolarize..and vis versa... but why?

it seems like it should be the opposite to me.

if there is an increased cation outside the cell membrane, doesn't that make the outside more positive, and relatively doesn't the cell have to be hyperpolarized?
I don't know what I'm missing...
I'll really appreciate it if someone helps me with this...
thanks a lot!

at normal resting mem potential which is -70mV, the cell interior is more negative than cell exterior.
next, whn an excitatory ( has to be excitatory..only thn..)impluse arrives at the cell mem. the na gated channls open causing influx of na --->increase of intracellular + charge.this changes the earlier equation, NOW THE CELL INTERIOR IS MORE POSTIVE THN EXTERIOR. HENCE CALLED DEPOLARIZATION.

IF AN INHIBITORY IMPULSE ARRIVES.. THE RMP MOVES FURTHER AWAY FROM -70MV.. IE.. IT BECOMES MORE NEGATIVE. HENCE CALLED HYPERPOLARIZATION.

I HOPE THIS HELPS

 

[aim high]

I got this from usmle and I just cannot understand this!

increase of extracellular sodium or potassium causes the cell to tend to depolarize..and vis versa... but why?

it seems like it should be the opposite to me.

if there is an increased cation outside the cell membrane, doesn't that make the outside more positive, and relatively doesn't the cell have to be hyperpolarized?
I don't know what I'm missing...
I'll really appreciate it if someone helps me with this...
thanks a lot!

ans)---i think its a simple logic...if there is increase in extracellular na or k..the memb potential ll be increase coz the difference between inside and outside potential is increased.. hence the increased na or k out side ll go inside n make the cell more positive and depolarise...if outside na or k is decreased ,the k and na inside ll come out of cell and make the cell more nagative and hence hyperpolarise the cell..

hope it helps..goodluck..