Action Potentials

Question 1

1. Depolarisation of a neurone

Answer 1

When the neurone receives an impulse from sensory receptors, sodium channels on the dendrites open, leading to the movement of Na+ ions into the cell causing depolarisation

Question 2

2. If depolarisation reaches the threshold potential…

Answer 2

If this depolarisation reaches the threshold potential it activates voltage-gated sodium channels causing an action potential.

Question 3

3. Repolarisation of a neurone

Answer 3

After Voltage-gated sodium ion channels close, and voltage-gated potassium channels open, causing Repolarisation as K+ ions leave the cell

Question 4

4. Hyperpolarisation

Answer 4

Outward diffusion of K+ ions causes hyperpolarisation and the voltage-gated potassium channels close

Question 5

5. Return to resting membrane potential

Answer 5

Finally, the Sodium potassium pump returns the cell to the resting membrane potential.

Question 6

What is the refractory period?

Answer 6

is the period in an action potential where the axon can’t be depolarised to initiate a new action potential. It limits the frequency of action potentials and ensures action potential are discrete & only travel in one direction.

Question 7

Nature of action potentials

Answer 7

Action potentials are an all or nothing response because once the threshold is reached each action potential always depolarises the axon to the same voltage by voltage-gated sodium channels.

Question 8

Draw an action potential diagram

Answer 8