Lecture 9: Modeling Cell Membrane into Electric Circuit PDF

Lecture 9 Modeling cell membrane into electric circuit Biophysics (PHY261) 9/12/2024 Equivalent Circuit Model for the Plasma Membrane The lipid bilayer, which represents ions to pass through will b...

Lecture 9 Modeling cell membrane into electric circuit Biophysics (PHY261) 9/12/2024 Equivalent Circuit Model for the Plasma Membrane The lipid bilayer, which represents ions to pass through will be represented as a Capacitor. Capacitance for a cell membrane is approximately 1 μF/cm2 The different types of ion channels embedded in the lipid bilayer will be represented as resistors, each has specific resistance (Conductance) (g = 1/R) Equilibrium potential for each ion is the electrical potential difference across the channel and is modeled as batteries Na+/K+ pumps are used in equal and opposite directions to these passive currents and can be modeled as generators. 2 Outside of the cell Inside the cell 3 4 5 6 7 What is the source of voltage 9 10 11 12 13 G=1/R I=V/R 14 15 16 Concentration Gradient Electrical Gradient 17 18 19 20 21 22 23 Since we have many leak channels for each ion, We will now represent all the leak channels of each ion by only one resistor with a total conductance of G G = SUM g 24 25 26 Na+/K+ pump is the Generator that charges the circuit. WHY? 27 28 29  Equivalent Circuit Model for the Plasma Membrane Now, We will represent all the leak channels for all of the ions by one equivalent resistance with a total conductance G. We will also represent the voltage-gated ion channels of K+ and Na+ ions as variable resistances. WHY? 30 GNa+ Variable GK+ Variable resistance resistance GL Equivalent equivalent to Na+ equivalent to K+ resistance of all Voltage-gated ion Voltage-gated leak channels channels ion channels 31 Questions? Questions?