Physiology: Origin of Membrane Potentials Flashcards
membrane potential (Em)
separation of opposite charges across the membrane
what happens in excitable cells when they’re excited
produce a rapid, transient change in Em
what types of cells are excitable
nerve and muscle
what causes cells to become excited
unequal distribution and selective movement of ions across the membrane
what are the conc. gradients for K+ and Na+
K+ is out, Na+ is in
at resting Em which ion is the membrane more permeable to
K+
what are the two opposing forces acting on K+
- conc. gradient, tending K+ out
- electrical gradient, tending K+ in
what is Ek
K+ equilibrium potential when the conc. and electrical gradients balance
what value is Ek
~-90mV
what are the two opposing forces acting on Na+
- conc. gradient, tending Na+ in
- electrical gradient, tending Na+ out
what value is ENa
~+60mV
what are the effects of Na+ and K+ on Em
large net K+ out moves Em towards -90mV, small net ok Na+ neutralising some of K+’s created potential
what value is Em
~-70mV
why is the value of Em closer to that of Ek than ENa but not identical to Ek
its closer to Ek due to its greater permeability but bot identical due to a small outward leak of Na+ down it s electrochemical gradient
how does Na/K ATPase affect Em
- maintains the Na+ and K+ gradients
- generates a hyperpolarising currents (more +ve out than in)
- adds variable amounts to Em depending on membrane resistance and cell activity
