Physiology 4 - Origins of membrane potential

Question 1

What is the membrane potential? (Em)Units?

Answer 1

Separation of opposite charges across the membranemV (the membrane itself is not charged)

Question 2

In terms of membrane potentials, what do excitable cells (e.g. nerve and muscle) have the ability to do?

Answer 2

Produce rapid, transient changes in their membrane potential when excited e.g. action potentials

Question 3

What is the is the resting membrane potential?

Answer 3

Constant in non-excitable cells and in excitable cells at rest

Question 4

What is the membrane potential due to?

Answer 4

Difference in the concentration and permeability of key ions

Question 5

Extracellular and intracellular concentration of Na+?Concentration gradient

Answer 5

E = 150I = 15Inward

Question 6

Extracellular and intracellular concentration of K+?Concentration outward?

Answer 6

E = 5I = 150Outward

Question 7

Relative permeability of sodium and potassium?

Answer 7

Na+ = 1K+ = 100

Question 8

Is the plasma membrane permeable to the large relatively negatively charged (anionic) intracellular proteins?

Answer 8

No - it is impermeable to these

Question 9

Is the inside or outside of the cell more negatively charged?

Answer 9

Inside

Question 10

Is the electrical gradient for K+ inwards or outwards?Is the concentration gradient for K+ inwards or outwards?

Answer 10

InwardsOutwards

Question 11

What is the equilibrium point?

Answer 11

The point where there is no net movement of charge (when the concentration gradient and electrical gradient balance each other out)

Question 12

What is the equilibrium point for K+?

Answer 12

-90 mV

Question 13

What does the negative sign before the equilibrium potential for K+ mean?

Answer 13

The polarity of the excess charge is on the inside of the membrane

Question 14

What can be calculated using the Nernst equation?

Answer 14

The equilibrium potential for any given ion

Question 15

What is the Nerst equation for a monovalent ion at 37 degrees?

Answer 15

Eion = 61log10([ion]o/[ion]i)

Question 16

Direction of electrical and concentration gradient for Na+?

Answer 16

Both inwards

Question 17

What is the equilibrium potential for Na+?

Answer 17

+60mV

Question 18

What effect does permeability for a given ion have on its tendency to drive membrane potential towards its own equilibrium potential?

Answer 18

The greater the permeability for a given ion, the greater the tendency for that ion to drive membrane potential towards the ion’s own equilibrium potential

Question 19

What effect does concurrent K+ and Na+ movement have on establishing the resting Em?Resting membrane potential

Answer 19

Relatively large net diffusion of K+ outward (higher permeability)Relatively small net diffusion of Na+ inward neutralised some of the potential created by K+ aloneResting membrane potential therefore = -70mV

Question 20

What can be used to calculate Em?

Answer 20

The Goldman-Hodgkin-Katz equation

Question 21

What is the Goldman-Hodgkin-Katz equation?

Answer 21

Em=61log10((PK+[K+]0 + PNa+[Na+]0) / (PK+[K+]i + PNa+[Na+]i))

Question 22

What does hyper polarisation mean?

Answer 22

a change in a cell’s membrane potential that makes it more negative

Question 23

What type of current does the Na+K+ATPase pump generate?

Answer 23

A hyper polarising current

Question 24

What does depolarisation mean?

Answer 24

Making it more positive

Question 25

What does repolarisation men?

Answer 25

the change in membrane potential that returns it to a negative value just after the depolarization phase of an action potential has changed the membrane potential to a positive value