Action Potentials

Question 1

What are the 5 stages of an action potential?

Answer 1

stimulus, depolarisation, repolarisation, hyperpolarisation and return to resting potential

Question 2

What is the resting potential difference of the neurone?

Answer 2

-70mV

Question 3

What happens when a stimulus occurs?

Answer 3

the neurone is excited and sodium ion channels open so sodium ions diffuse into neurone down the electrochemical gradient making the inside less negative

Question 4

What happens if the potential difference reaches the threshold value?

Answer 4

(-55mV) depolarisation occurs and voltage gated sodium ion channels open allowing more sodium ions in so potential difference increases

Question 5

When does repolarisation occur?

Answer 5

Once the potential difference reaches +30mV, sodium ion channels close and voltage gated potassium ion channels open so K+ ions diffuse out lowering the potential difference back to resting potential

Question 6

What is hyperpolarisation?

Answer 6

K+ ion channels are slow to close so potential difference becomes more negative then resting potential (less than -70mV)

Question 7

How does potential difference return to resting potential?

Answer 7

K+ ion channels finally close and Na+/K+ pump restarts and axon returns to resting potential

Question 8

What does a bigger stimulus cause? Why?

Answer 8

more frequent action potentials as action potential is always the same as long as threshold value is met

Question 9

How are action potentials sped up?

Answer 9

neurones which are myelinated so the impulse is insulated and depolarisation only occurs at nodes of ranvier