Membrane potential I-II Flashcards
electric vs osmotic force
Electric are much stronger (i.e. few excess ions needed to counter large concentration differences)
two forces acting on ion movement
concentration difference and electrical potential difference across the membrane. Together they form VOLTRON!!! ? no wait electrochemical gradient
equilibrium potential
electrical potential difference across membrane that must exist if the ion is to be at equilibrium. Specific to 1 ion. When equilibrium potential = membrane potential, electrochemical equilibrium. Often not the case (except when dead) due to impermeable membranes or ion pumps
membrane potential
measure of the real difference in coltage between the internal environment and the ECF
ion pump
pumps pushes ions such that Vm and E grow apart (ie against gradient), look at []I vs []o and charge of ion vs membrane potential. If they are in same direction, pump goes opposite, if different compare equilibrium potential to membrane potential
charge of solution
bulk of solution is neutral, only a small ion difference make ICF negative
Donnan rule
products of the ion concentrations inside the cell must equal the product of the ion concentrations outside cell
osmotic balance
mosM inside = outside
charge neutrality
assume cations and anions inside and outside cell are equal
Nernst eq
E=-60*log([]o/[]i)
sodium potassium pump
1 ATP used to move 3 Na+ ions outside cell and 2 K+ ions inside the cell
steady state
state of a real cell, requires constant input of energy to maintain proper gradient levels
relative permeabilities
determines memb rane potential, Na/K pump does not
driving force
difference between Vm and Eion
neurons
Vm is close to E of K+. Sensitive to [K+] is high because of low concentrations outside cell. Unlike Na+
