Electrical Excitability - Action Potential

Question 1

What is meant by the all or nothing effect in action potentials?

Answer 1

Action potentials will occurs if the threshold for depolarisation is reached, and the size and intensity of the action potential will not vary on a given cell.
If the threshold is not reached nothing will happen.

Question 2

How does the speed of an action potential in an axon differ to that in the heart?

Answer 2

They are much quicker in the axon (0.5ms : 100ms)

Question 3

Where on the axon does the threshold potential have to be achieved?

Answer 3

The axon hillock (initial segment)

Question 4

What happens to action potentials if there is change in equilibrium potential?

Answer 4

If the equilibrium potential causes the membrane to have a less positive resting potential than the depolarisation threshold level then action potentials won’t occur as this threshold won’t be reached.

Question 5

How big of a difference to sodium concentration does an action potential have?

Answer 5

It causes a very small difference, and as the diameter of the axon increases the percentage change in concentration decreases.

Question 6

What does an increase in conductance for a particular ion represent?

Answer 6

That there is an increase in the number of channels open for that ion.

Question 7

What are the main functions of the sodium potassium ATPase?

Answer 7

It is important for maintaining the ion concentration across the membrane and also stops the positive feedback loop so the sodium channels don’t just remain open and allow influx of sodium.

Question 8

What is the order of the stages of the sodium channels?

Answer 8

The channels go closed - open - inactivated

Question 9

What affects the speed of conduction velocity in axons?

Answer 9

The diameter of the axon and whether the axon is myelinated.