Membrane Potential

Question 1

Potential is measured in what? What does it allow?

Answer 1

Voltage!

Gives the ability to do work via separation of charge

Question 2

Resting membrane potential

Is it active?
What is an excitable cell?
Normal charge of an excitable cell?
Is this in steady state or equilibrium ?

Answer 2

Cell at rest = inactive
An excitable cell == the inside is NEGATIVE

-65/-70

This would be in steady state, NOT equilibrium!

Question 3

Depolarization

Answer 3

Movement of membrane potential towards zero!

Question 4

Hyperpolarization

Answer 4

Movement of membrane potential away from zero!

Question 5

Current =

What is it measured in???

Answer 5

Movement of charge

Measured in Amperes (A)!

Movement specifically of ions!!!

Question 6

Resistance (R) =

What is it measured in?

Answer 6

Opposition of the flow of charge!!

Measured in Ohms!

Question 7

Ohm’s Law….

Answer 7

Voltage = Current x Resisistance

V = I x R

Voltage –> Potential!!!!!

Question 8

Conductance

What letter represents this?

What are the units?

What is the relationship of conductance with resistance?

Answer 8

= ease of flow of a current through an ion channel!

Symbol == g

Units == Siemens (S)

Inverse of resistance
== g=1/R

Takes into account ALL IONS!!!

Question 9

Na+/K+ Pump…..

What is the electronic effect???

Answer 9

3 Na+ OUT
2 K+ IN

+1 electronic effect outside of the cell

Question 10

What are the 2 roles of the resting membrane potential???

Answer 10

1. Indirect = MOST IMPORTANT – the fact that there is a gradient that exists (more Na+ outside and K+ inside)
2. Direct = electrogenic effect
   - — the pump puts 1 net Na+ outside the cell

Question 11

What does Digitalis do???!

Answer 11

Inhibits the Na+/K+ Pump!

Blocking this will cause a small Shift/depolarization

Only by 5-10 mV!

Question 12

Ion distribution…

Know amount in/out and also the relative permeability!

Na+?
K+?
Organic A-?
Cl-?

Answer 12

Na+

• 5 IN, 145 OUT
• perm = 1

K+

• 145 IN, 5 OUT
• Perm = 50-75!!!!

Organic A-

• 140 IN, 0 OUT
• Perm = 0

Cl-

• 10 IN, 150 OUT
• Perm = 1

Question 13

Equilibrium reversal potential

Answer 13

= voltage that it would equilibrate at

Question 14

Nernst Equation?

What does it solve for?

Answer 14

Ex = 61/z x log (Conc. Out/Conc In)

Z = charge of ion!!

It solves for the equilibrium potential… or voltage at which the ion will be in equilibrium!

Question 15

Does Na+ or K+ have a higher resting permeability?

Answer 15

K+ has a much higher resting permeability because the cell is much more permeable to K+

Question 16

What is the number 1 contributor to membrane potential?

Answer 16

K+ moves out of the cell a lot due to high permeability. This creates the negative charge inside the cell!!

Question 17

Electrogenic effect accounts for how much charge difference?

Answer 17

5-10 mV!

Question 18

The smaller the Na+ Permeability….

Answer 18

The closer Em will be to Em