Action potential (4)

Question 1

What are the three types of channels involved in creating an action potential?

Answer 1

1. sodium ion channels/ Na+ channels (which are voltage-gated)
2. potassium ion channels/ K+ channels (which are voltage-gated)
3. sodium-potassium pump (which uses energy from ATP to pump 3Na+ out of the cell while pumpnig 2K+into the cell)

Question 2

What are the 5 stages of action potentials? (just name them)

Answer 2

1. Stimulus
2. Depolarisation
3. Repolarisation
4. Hyperpolarisation
5. Resting potential

Question 3

What happens at the first stage of an action potential?

Answer 3

STIMULUS

A stimulus excites the neurone cell membane and causes Na+ channels to open. The membrane then becomes more permeable to Na+ and Na+ diffuses into the neurone down an electrochemical gradient. This makes the inside of the neurone less negative.

Question 4

What happens at the second stage of action potentials?

Answer 4

DEPOLARISATION

If the potential differences reaches or surpassed the threshold more sodium ion channels open (an example of positive feedback) and more Na+ diffuses into the neuron. This depolarises the inside of the axon becomes more positive than the outside.

Question 5

What happens at the third stage of an action potential?

Answer 5

REPOLARISATION

At a potential difference of around +30mV the sodium ion channels close and the potassium ion channels open. The membrane is then more permeable to potassium ions so they diffuse out of the neurone down their concentration gradient. This reduces the voltage and starts to get the membrane back to its resting potential.

Question 6

What happens at the fourth stage of an action potential?

Answer 6

HYPERPOLARISATION

potassium ion channels are slow to close so there is an ‘overshoot’ where too many potassium ions diffuse out of the neurone the potential difference becomes more negative than the resting potential.

Question 7

What happens at the fifth and final stage of an action potential?

Answer 7

RESTING POTENTIAL

the sodium ion channels are closed and the potassium ion channel is opened. The sodium-potassium pump returns the membrane to its resting potential so it can be excited by another stimulus.

Question 8

How does an action potential travel along a neurone?

Answer 8

It travels as a wave of depolarisation which works kind of like a mexican wave.

Question 9

What is the refactory period and why is it needed?

Answer 9

The refactory period is a period of recovery which the resting potential is being restored. This acts as a time delay between one action potential and another which ensure action potentials don’t overlap but pass as discrete (separate) impulses. It also ensures that action potentials are unidirectional (only travel in one direction) as an action potential cannot be propegated during the refactory period so the impulse can’t go backwards.

Question 10

What’s the effect of anaesthetic on action potentials?

Answer 10

the anaesthetic binds to sodium ion channels in the membrane of the neurone and stops Na+ from moving into the neurone. This means there is not an infulx of sodium ions so the membrane will not depolarise. This stops action potentials from being conducted along the neurones and reaching the brain. So you don’t feel pain.