Resting Membrane Potential

Question 1

What is membrane potential?

Answer 1

Electrical potential (voltage) difference across plasma membrane

Basis of signalling (esp CNS)

Question 2

How do you measure membrane potential?

Answer 2

Microelectrode (fine glass pipette)
Penetrates cell membrane
Filled with conducting solution (KCl)

Question 3

How is a membrane potentil expressed?

Answer 3

Potential inside the cell relative to the outside

Question 4

Resting membrane potential cardiac myocyte?

Answer 4

-80 mV (millivolts)

Question 5

RMP neurones?

Answer 5

-70 mV

Question 6

RMP skeletal muscle?

Answer 6

-90 mV

Question 7

RMP smooth muscle myocytes?

Answer 7

• 50 mV

Question 8

How is selective permeability achieved in cell membrane?

Answer 8

Phospholipid bilayer (hydrophobic interior)

Ion channels (aqeous pore allows ions to diffuse)

Channel proteins (gated - open and close dependent on conformational change) 
= rapid ion flow down electrochemical gradient

Question 9

How does the resting membrane potential arise?

Answer 9

Selectively permeable to K+
Chemical diffusion gradient out of cell

(Potassium leaves, anions are left inside cell)

Question 10

What is equilibrium potential?

Answer 10

When electrical and chemical gradients balance and there is no net driving force across membrane

Question 11

Equation for calculatin equilibrium potential

Answer 11

Nernst equation

Question 12

What do you have to know to calculate equilibrium using Nernst equation?

Answer 12

Extracellular and intracellular concentrations
Temp in kelvins (310.6 for body temp)
Valency (+1 for K+)

Question 13

What occurs if membrane is selectively permeable to that ion alone?

Answer 13

Its membrane potential would be the equilibrium potential

Question 14

What channels dominate resting membrane?

Answer 14

Open K+ channels

Question 15

What occurs if Na+ and Ca+ leak in?

Answer 15

Diminish -ve potential

Depolarise membrane

Question 16

Cardiac muscle and nerve cells channels

Answer 16

-80/-70 mV

Resting potential close to K+ equilibrium (-95mV)
Not perfectly selective for K+

Question 17

Cells with more +ve resting potentials

Answer 17

Smooth muscle cells (-50mV)

Lower sensitivity for K+ as increased contribution from other channels

Question 18

Skeletal muscle channels

Answer 18

Many Cl- and K+ channels open

Resting potential -90mV - very close to equilibrium of Cl- and K+