Membrsne Potential And Action Potenital

Question 1

Ion flux

Answer 1

The number of ions that cross a unit area per unit time m-2.s-1

Question 2

Why are ion channels needed

Answer 2

Lipid cell membranes are barriers to ion movement and separate ionic environments
Permeable pores open and close depending on transmembrane voltage

Question 3

Are ion channels selective

Answer 3

Yes to different types of ions eg sodium and chloride ions
Movement across membrane occurs when the ion concentrations are different

Question 4

Equilibrium potential

Answer 4

The potential at which electrochemical equilibrium has been reached which prevents diffusion of ions down its conc gradient

Question 5

Nernst equation

Answer 5

Measured equilibrium potential

Question 6

How can you simplify nernst equation

Answer 6

• Assume T = 37oC = 310K
• Convert ln to common log
• state E in mV
• Typical concentrations of K+:
  150 mM inside and 5 mM outside
• Typical concentrations of Na+:
  10 mM inside and 150 mM outside

Question 7

What does the Goldman-Hodgkin-Katz equation calculate?

Answer 7

Membrane potential of the cell

Question 8

Depolarization

Answer 8

Em becomes more positive

Question 9

Repolarisation

Answer 9

‘Em decreases towards resting potential

Question 10

Overshoot

Answer 10

Membrane potential (em) becomes more positive than 0mV

Question 11

Hyperpolarisation

Answer 11

Em decreases beyond resting potential

Question 12

Graded potentials

Answer 12

When sensory body e.g. touch receptor, is stimulated by external stimulus or neurotransmitters it produces a change in membrane potential

Question 13

What happens to graded potential over time

Answer 13

They decay over the length of the axon as charge leaks from axon

Question 14

5 phases of action potential

Answer 14

1)resting membrane potential- permeability for k+>permeability for Na+.
2)depolarization-stimulus depolarises membrane potential becomes more positive
3)upstroke-starts at threshold potential ,increase in sodium permeability because VGCSs open and VGKCs start to open slowly
4)repolarisation-decrease in Na+ permeability as VGSCs close but k+ ions continue to leave so becomes more negative
5) after hyperpolarisation VGKCs begin closing and em returns to resting potential

Question 15

Relative refractory period

Answer 15

Period of time where you need a stronger than normal stimulus to trigger another action potential
Less sodium ion channels are open

Question 16

Absolute refractory period

Answer 16

Period where inactivation gate of VGSC is closed and so a new action potential cannot be triggered

-

Question 17

Passive propagation

Answer 17

• Only resting K+ channels are open
• This is where graded potentials decay as they get further from site of depolarisation

Question 18

Active propagation

Answer 18

1) AP forms, Na+ fluxes into cell

2) Near this area, a local depolarisation is caused by local current flow which depolarises this adjacent region to where the AP is forming

3) Adjacent region moves from resting Em and gradually depolarises to threshold value and when that’s reached, VGSCs open in that area → produces another upstroke and new AP at that area

4) Old active region is gradually returning to its resting Em because K+ channels open and K+ leaves cell

This is gradual movement of AP down neurone axon

Question 19

Where are voltage gated channels located

Answer 19

Nodes of ranvier
Allow saltatory conduction

Question 20

What two factors affect conduction velocity

Answer 20

Axon diameter
Myelin thickness
Increasing axon diameter means greater conduction velocity is faste action potential

Question 21

When does conduction velocity decrease

Answer 21

With reduced diameter eg regrowth after injury,reduced myelinate in eg multiple sclerosis,cold,anoxia,compression and drugs