Origin of Membrane Potentials Flashcards
what is the membrane potential
the separation of opposite charges across the membrane
*all cells have membrane potential
what is responsible for the potential difference across a membrane
when there is a membrane potential (ie if the ICF has more negative ions than the ECF) the polar ions gather up along each side of the membrane
ie the separated charges are responsible for the potential difference
what is Em
the difference in charge between the thin layers of the ECF and ICF located next to the inside and outside of the membrane
when would you find a resting membrane potential
in non-excitable cells
and
in excitable cells at rest
what direction does sodium travel down the concentration gradient
inward
what direction does potassium travel down the concentration gradient
outward
what are cations
positively charged ions
ie sodium and potassium (their electrical gradient will always be towards the negatively charged side of the membrane)
when is the membrane more permeable to potassium than sodium
when it is at resting potential
when considering the equilibrium potential for potassium - what are the two opposing forces acting on potassium
- the conc. gradient (tending to move K out of the cell)
2. the electrical gradient (tending to move K into the cell)
what happens when the two opposing forces acting on K balance each other
there is no further net movement of potassium
what is Ek ( E (K))
the equilibrium potential for K
= -90mV (inside the cell)
what is the Nernst equation
an equation to calculate the equilibrium potential for any ion
what is E (Na)
+61mV
what is the resting membrane potential (Em) for a typical nerve cell and what is it due to
relatively large efflux of K making the Em lean toward Ek (-90mV) however there is a small influx of sodium ions which neutralises some of the potential (-70mV)
what is the Goldman-Hodgkin-Katz equation and when can we use it
to calculate the Em
if we know: ion concentrations inside and outside the cell and the relative membrane permeability for each ion
what effect does the sodium/potassium pump have on the Em
> creates a hyperpolarising current
ie 3Na out and only 2K in, loses a positive charge with every ATP molecule split
> also helps maintain transmembrane sodium and potassium concentration gradients
why is the Em important
the Em has specialised use in nerve and muscle cells ie membrane permeabilities are altered rapidly and transiently in repose to certain stimuli > resulting in fluctuation in the Em
*eg changes in the Em is linked to the secretion of insulin from pancreatic B-cells
what is the single most important factor in setting the Em
the potassium gradient
at rest - what is Em
-83mV
