Action potential

Question 2

What is an action potential?

Answer 2

an increased voltage beyond a set point, generating a nervous impulse

Question 3

What is depolarisation and why does it occur?

Answer 3

an increase in voltage, which occurs as the membrane becomes more permeable to Na+

Question 4

How does the action potential move along an axon?

Answer 4

similarly to a mexican wave

Question 5

What protein channels are voltage dependent?

Answer 5

voltage-gated Na+ channels

Question 6

How might a stimulus cause depolarisation?

Answer 6

as it may allow voltage-gated Na+ channels to open, allowing Na+ ions to diffuse in, meanwhile K+ ions still diffuse out

Question 7

What happens if the voltage is raised above the threshold?

Answer 7

More Na+ ions can move into the cell, so voltage increases further

Question 8

What is the maximum voltage an axon can reach?

Answer 8

+40mV

Question 9

What happens at +40mV?

Answer 9

more K+ channels are opened, and voltage-gated Na+ channels close. This causes voltage to decrease

Question 10

What is the refractory period?

Answer 10

where voltage goes temporarily below the resting potential

Question 11

What are the different stages in generating an action potential?

Answer 11

resting, depolarisation, repolarisation, hyperpolarisation, resting

Question 12

Why do action potentials move across an axon like a mexican wave?

Answer 12

as one part reaches +40mV, the voltage is enough to trigger the next part (nodes of Ranvier) of the axon to start depolarisation

Question 13

What happens if the voltage does not pass -55mV?

Answer 13

nothing, the action potential and impulse are not produced

Question 14

Why does a depolarisation that does not reach the threshold not cause an action potential?

Answer 14

not enough energy to open voltage gated Na+ channels

Question 15

What does a bigger stimuli cause?

Answer 15

a greater frequency

Question 16

Why is the all or nothing principle important?

Answer 16

makes sure animals only respond to large enough stimuli, rather than the animal becoming overwhelmed

Question 17

What does the refractory period mean?

Answer 17

action potential cannot be stimulated, as the Na+ channels are recovering

Question 18

Why is the refractory period important?

Answer 18

• only discrete impulses are produced
• only travel forwards in one direction
• limits the number of impulse transmission

Question 19

Why is it important that impulses are discrete?

Answer 19

so each action potential is separate and therefore information can be processed in more detail

Question 20

Why is it important that action potentials only travel forwards?

Answer 20

if it wasnt, Na and K+ ions would spread out, preventing the threshold from ever being met and therefore preventing a response

Question 21

Why is it important that the number of action potentials are limited?

Answer 21

it prevents over reaction to a stimulus which could result in overwhelming the sense, hindering survival