What electrical component is the lipid bilayer?

What is the associated equation?

Electrical capacitor

Q = C V

Q - total charge (coulombs)

V - voltage or “concentration of charge” (Volts)

C - capacitance - a constant - the ability to store charge

C = Q/V : The capacitance is a measure of the amount of charge stored for a given voltage.

Cm - Specific Membrane Capacitance

Charge stored increases linearly w/ surface area of membrane

What's the significance of Capacitance being a constant?

Q=CV

increase in charge means increase in voltage and vice versa

What determines the magnitude of membrane potential?

the number of opposite charges separated by the membrane

What electrical componants are ion channels?

What is the associated equation?

**Electrical resistors**

General expression of Ohms Law:

V = I R

V - Voltage

I - Current - the “movement of charge” - dQ/dt (coulombs/sec)

R - Resistance to the movement or flow of charge (ohms)

How is conductance defined?

General expression of Ohms Law(cont):

I = V/R

**Define “conductance” (G) as 1/R** (ohms-1 or Siemens)

**I = G V**

What equations apply to total membrane resistance and single channel resistance?

Total Membrane Resistance: Rm(refers to the total resistance of an area of plasma membrane)

V_{m} = I_{ion} R_{m}

Single Channel Resistance: rop (refers to the resistance of a single open channel)

V_{m} = i r_{op}

What determines total membrane resistance?

# of ion channels in the open state

What type of circuit is the plasma membrane?

Parallel RC Circuit

-Capacitance responsible for storing charge.

–Increased capacitance = Conduction Block

–Membrane Resistance due to Ion Channels.

–Ion Channel Dysfunction = Disease

Capacitative Current

(two equations)

Capacitance : Charge and Current

(two equations)

Current is defined as the “movement of charge”

I = dQ/dt (coulombs/sec)

I_{cap} = dQ/dt = C (dV/dt)

Q = CV

I_{cap} = C (dV/dt)

Apply a current to a Resistor - How does voltage change with time?

Voltage increases linearly as applied current increases

What happens as current is continuously injected in RC Circuit?

(a) All injected current initially goes to capacitor.

(b) After capacitor is charged, all injected current goes to resistor.

(c) When injected current is turned off, the charge accumulated on the capacitor leaks through the resistor (“capacitative discharge”)