2.1 Membrane, Action and Postsynaptic Potentials

Question 1

At rest, how is the inside of a neuron charged with respect to the outside?

Answer 1

negatively

Question 2

What are the two processes that establish the resting membrane potential?
What do they both involve?

Answer 2

• a passive process
• an active process: requires energy
  They both involve ions (molecules that have gained/lost an electron.

Question 3

What ions are found in a cell?
Are they positively or negatively charged?

Answer 3

positively:
- potassium
- sodium
- calcium

negatively:
-chloride

Question 4

How do the ions found in a cell make a resting membrane potential arise?

Answer 4

• the ions are unevenly distributed across the membrane
• there are more negative ions on the inside and more positive ions on the outside

Question 5

How does the passive process lead to a resting membrane potential?

Answer 5

• at rest, the cell membrane is largely impermeable to many ions (they bounce off)
• potassium is an exception
• selective diffusion through channels of potassium establishes a membrane potential
• as when K+ ions leave, they produce an electrical current
• this results in a separation of charge: solutions either side of the membrane are no longer electrically neutral

Question 6

How does the active process lead to a resting membrane potential?

Answer 6

• sodium-potassium pump (takes out sodium and brings in potassium)
• this is an active process, requiring energy supplied by ATP
• there is three sodium ions for every two potassium ions (3:2)
• other pumps redistribute other ions so you end up with an imbalanced concentration inside and outside the cell

Question 7

What is depolarisation?

Answer 7

when the membrane potential is made less negative (above-70)

Question 8

What is hyperpolarisation?

Answer 8

when the membrane potential is made more negative (below -70)

Question 9

At what level is a membrane polarised?

Answer 9

-70

Question 10

What is a ‘voltage gated’ channel?

Answer 10

opens when the cell is depolarised

Question 11

How is an action potential triggered?

Answer 11

the membrane is depolarise to the threshold

Question 12

What happens when a membrane is depolarised to the threshold?

Answer 12

• NA+ channels open and polarity reverses to +30 inside the cell
• this restores the RMP

Question 13

What makes the action potential conduction quicker?

Answer 13

• myelin: fatty sheath
• acts as an electrical insulator

Question 14

What underlies the upsweep of an action potential?

Answer 14

sodium channels

Question 15

What partially underlies the upsweep of an action potential?

Answer 15

potassium channels