voltage-activated Na+ and K+ channels and the refractory period

Question 1

describe the properties of both the voltage-gated Na+ and K+ channels

Answer 1

both are highly selective for their cations

both activated by membrane depolarisation, Na+ rapidly and K+ with a slight delay

Question 2

describe what it means to say the voltage-gated Na+ channel is self-reinforcing

Answer 2

the opening of a few channels causes more channels to open, causing further depolarisation (this is positive feedback)

Question 3

describe what is meant to say the voltage-gated K+ channel is self-limiting

Answer 3

outward movement of K+ causes repolarisation which turns off stimulus for opening, this is negative feedback

Question 4

describe the inactivation of the voltage-gated Na+ channels

Answer 4

channel enters non-conducting inactive state as a result of maintained depolarisation

Question 5

what is repolarisation required for after the voltage-gated Na+ channel is inactivated

Answer 5

required for channel to enter closed state in order to be ready for opening and generation of a further action potential

Question 6

what is responsible for the refractory period of the voltage-gated Na+ channels

Answer 6

inactivation of the channel, which also contributes to the repolarising phase of the action potential

Question 7

describe what the absolute refractory period is

Answer 7

no stimulus, no matter how strong, can induce a second action potential (all Na+ channels are inactivated)

Question 8

describe what the relative refractory period is

Answer 8

a stronger than normal stimulus can induce a second action potential, mixed between inactivated and closed state Na+ channels, also membrane is hyperpolarised