lecture 3 notes

Lecture 3:  

Ion gradients and membrane permeability properties establish membrane potential  

• Na/K ATPase moves Na and K across the membrane to establish and maintain the normal ECF and ICF concentrations which results in a chemical gradient for Na to move into the cell and for K to move out  

• Nerve cells have a relatively large number of K leak channels and the existence of these channels means the resting cell is relatively permeable to K  

• There is a strong chemical gradient driving K out of the cell so K exist the cell via the leaky channels and carries the positive charge out with it making the cell slightly more negative  

• However since K carries a positive charge, and the cell is inside negative, there is now an electrostatic attraction bringing K back into the cell  

• As K continues to move out of the cell down its chemical gradient, the magnitude of the voltage difference across the membrane increases therefore the electrostatic force bringing K back into the cell increase too  

• Eventually the cell will reach a point at which the outward movement of K is exactly matched by the inwards movement of K and this is called the equilibrium potential/electrochemical equilibrium  

• At each moment in time, the membrane potential depends on the concentration gradients of ions and relative permeability of membrane for ions 

• RMP is close to E_k  

• See slides for equations  

• The resting membrane is ~50-100x more permeable to K than to Na  

• Triggered change in membrane potential is typically called a local potential and local potentials may interact to initiate action potentials