L4 Electrical Components of Plasma Membrane

Question 1

What electrical component is the lipid bilayer?

What is the associated equation?

Answer 1

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

Question 2

What’s the significance of Capacitance being a constant?

Answer 2

Q=CV

increase in charge means increase in voltage and vice versa

Question 3

What determines the magnitude of membrane potential?

Answer 3

the number of opposite charges separated by the membrane

Question 4

What electrical componants are ion channels?

What is the associated equation?

Answer 4

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)

Question 5

How is conductance defined?

Answer 5

General expression of Ohms Law(cont):
I = V/R

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

Question 6

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

Answer 6

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

Question 7

What determines total membrane resistance?

Answer 7

of ion channels in the open state

Question 8

What type of circuit is the plasma membrane?

Answer 8

Parallel RC Circuit

-Capacitance responsible for storing charge.
–Increased capacitance = Conduction Block
–Membrane Resistance due to Ion Channels.
–Ion Channel Dysfunction = Disease

Question 9

Capacitative Current

(two equations)

Capacitance : Charge and Current

(two equations)

Answer 9

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)

Question 10

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

Answer 10

Voltage increases linearly as applied current increases

Question 11

What happens as current is continuously injected in RC Circuit?

Answer 11

(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”)