given as inside vs. outside. for example if the voltmeter indicates -65 that mean inside 65mv more negative than outside
Membrance potential at rest
At rest more negative ions on inside of membrance than rest
Equilibrium potential for K is negative
- 20 times more k+ inside (same as real nerve cell)
- A-=anions (any negative ion) nothing happens w/o ion channels
What happen K+ selective channels?
Insert K+ selective channels in membrance diffusion pushes K+ outside, anions left behind -electrical force develops that pulls K+ ions back inside
What happen at equilibrium?
- Electrical force equals diffusion force, but oppostie direction. Equilibrium potential is voltage when electrical and diffusion forces balanced, no net K+ movement.
- diffusion force=electrical force
Equilibrium potential for Na is positive
10 times more NA+ outside cell
what happen with NA+ selective ion channels?
If NA+ selective ion channels in membrance NA+ flows into cell b/c diffusion force
what happen at NA+ equilibrium potential?
Inside of cell becomes more and more positive until electrial force repels positive Na+ ions at equilibrium potential the diffusion forces pushing Na+ ion in is exactly counterbalanced by the electrial force pushing them out.
Each ion has its own equilibrium potential
- Ek+, Ena+,Eca2+, Ecl-
- -equilibrium potential depends on concentration of that ion inside + outside cell
- -can be calculated w/nernst equation
- Eion=23 times RT/ZF times log [ion]outside/[ion]inside
- R is gas constant
- T absolute temp
- Z charge of ion=+1 for k+/na+,+2 for ca2+,-1 for Cl-
- F Faraday's constant
- ion= outside concentration of ion outside cell
Nernst Equation at bodytempeture
Eion=61.5/z time log[ion]outside/[ion]inside
The equilibrium potential is?
Equilibrium potential is the membrane potential we measure when membrane is permeable to that ion alone. ex if only K+ ion channels in membrane, and 20times more K+ inside we get a membrance potential of -80mv. if only Na+ channels in membrane and 10 times more Na+ inside membrance potential is +61.5mv
Resting membrance potential
resting membrane potential of -65mv is close to ,but not at , equilibrium potential for K+, at rest membrane has mostly K+ channels open.