The Nernst Equation RT TI ZF LXIB Where Ex equilibrium potential of X R ideal gas constant T absolute temperature charge number of the ion F Faraday's number Xl natural logarithm of concentration ration [X lOof X+ on the two sides of the membrane
The Nernst Equation B A X A B X X zF RT E E E [ ] [ ] ln + + = − = − Where EX equilibrium potential of X+ R ideal gas constant T absolute temperature z charge number of the ion F Faraday’s number natural logarithm of concentration ration of X+ B on the two sides of the membrane A X X [ ] [ ] ln + +
At any membrane potential other than the ex, there will be an electrochemical driving force for the movement of X+ across the membrane, which tend to pull the membrane potential toward its Ex The greater the difference between the membrane potential and the Ex will result in a greater driving force for net movement of ions Movement can only happen if there are open channels
• At any membrane potential other than the Ex , there will be an electrochemical driving force for the movement of X+ across the membrane, which tend to pull the membrane potential toward its EX . • The greater the difference between the membrane potential and the EX will result in a greater driving force for net movement of ions. • Movement can only happen if there are open channels!
Distribution of lons Across plasma Membranes of a human skeletal muscle cell EN =+65 mV E1=-90mV Na+ =145 mM C|-=115mM Na+=12 mM Cl-=3.6 mM K+=160mM ++++十 90 mV (resting membrane potential K+=3.5mM 100mV
Distribution of Ions Across Plasma Membranes of a human skeletal muscle cell
2. RESTING MEMBRANE POTENTIALS The cytoplasm is usually electrically negative relative to the extracellular fluid. This electrical potential difference across the plasma membrane in a resting cell is called the resting membrane potential
2. RESTING MEMBRANE POTENTIALS The cytoplasm is usually electrically negative relative to the extracellular fluid. This electrical potential difference across the plasma membrane in a resting cell is called the resting membrane potential
微电极 3M KCI 生理盐溶液 细胞 A浴槽一 B 电极刺入前 电极刺入后 图1-11细胞的静息膜电位