Ions, Permeability and the Resting Potential

Question 1

What are the three most important factors which determine the ‘passive’ movement of ion across the membrane?

Answer 1

electrical gradient, concentration gradient, membrane permeability

Question 2

What is the Nernst equation (the equilibrium potential)?

Answer 2

Ex=61 log10[X]1/[X]2

Question 3

Describe the origin of the resting membrane potential

Answer 3

more K+ than Na+ gates are open, making the membrane more permeable to K+ (therefore a negative value)

Question 4

If the K+ permeability increased by a factor of 50, how would the Em be affected?

Answer 4

It would be hyperpolarised

Question 5

If the sodium permeability increased by a factor of 100, how would Em be affected?

Answer 5

Depolarisation

Question 6

What is the threshold potential?

Answer 6

The minimum membrane potential that must be reached in order for an action potential to be generated.

Question 7

What is the effect of increasing the extracellular K+ concentration to 10mV?

Answer 7

depolarisation and movement of the resting membrane potential nearer to threshold

Question 8

What is the effect of decreasing the extracellular K+ concentration to 2mV?

Answer 8

Hyperpolarisation and movement of the resting membrane potential away from the threshold

Question 9

What is the effect of varying the extracellular K+ concentration on Em?

Answer 9

increasing the extracellular K+ concentration rapidly increases the membrane potential (mV) (becoming more positive)

Question 10

What is the effect of varying the extracellular Na+ concentration on Em?

Answer 10

increasing the extracellular Na+ concentration only increases the membrane potential (mV) slightly

Question 11

Resting potential of cardiac action

Answer 11

-90mV

Question 12

What is the time called during which another action potential is impossible; limits maximal firing rate?

Answer 12

absolute refractory period

Question 13

How does repolarisation of ventricular cells differ to neurons?

Answer 13

Not as quick as neurons

Question 14

What causes cardiac depolarisation?

Answer 14

associated with opening of fast sodium channels

Question 15

What keeps the depolarisation phase of cardiac cells open for longer?

Answer 15

increased calcium permeability

Question 16

What closing of sodium channels triggers?

Answer 16

opening of calcium channels

Question 17

(when calcium permeability increases) where calcium binds

Answer 17

receptors on the ER

Question 18

What causes a muscle contraction?

Answer 18

caused by release of intracellular calcium

Question 19

What is the cause of K+ channels opening in cardiac cells?

Answer 19

closing of calcium channels

Question 20

What is Na+ channel reactivation dependent on?

Answer 20

both time and voltage

Question 21

What is the effect of giving KCl to patient?

Answer 21

by preventing repolarisation back to the membrane potential, the high extracellular K+ inhibits the reactivation of the Na+ channels and further action potentials - therefore heart can’t beat again

Question 22

Why does changing the extracellular concentration of K+ have a greater effect on the membrane potential than changing the extracellular Na+ concentration?

Answer 22

the membrane is more permeable to K+ than it is to Na+

Question 23

concentration of extracellular K+ that Em=0mV

Answer 23

140mM

Question 24

why 140mM of K+ gives an Em = 0

Answer 24

the intracellular and extracellular K+ concentrations are equal

Question 25

(peak of the action potential) 30mV

Answer 25

membrane is more permeable to Na+ than it is to K+