4.1 - The Action Potential And Its Properties

Question 0

Why does repolarisation occur?

Answer 0

• inactivation of Na+ channels

- opening of voltage-gated K+ channels

Question 1

What are the key features of an action potential?

Answer 1

• Generated when membrane potential exceeds a certain threshold
• depends on ion gradients and relative permeability of the membrane
• all or nothing
• propagated without loss of signal

Question 2

Why does hyperpolarisation occur?

Answer 2

The K+ channels take time to close

Membrane potential drops to around -88mV

Question 3

How is the membrane potential brought back to -70mV after hyperpolarisation?

Answer 3

Flickering of other ion channels

Question 4

Why are action potentials ‘all or nothing’

Answer 4

The Na+ channels are voltage-gated so as the membrane becomes more positive, positive feedback means more channels will open.
This means depolarisation can’t stop half way

Question 5

What is the absolute refractory period?

Answer 5

When almost all the Na+ channels are I’m the inactivated state so no action potentials can be generated

Question 6

Define relative refractory period

Answer 6

Na+ channels are recovering from inactivation so some are open while others are closed
An action potential can be generated but the threshold for an action potential is higher

Question 7

Define accomodation

Answer 7

The larger a stimulus is the larger the depolarisation necessary to initiate an action potential as more Na+ channels have been inactivated

Question 8

How do local anaesthetics work?

Answer 8

They block Na+ channels