The Action Potential

Question 1

What is the name of the point at which the Vm of a cell must rise above for it to trigger an action potential and depolarise?

Answer 1

The threshold potential

Question 2

Explain the positive feedback and spontaneous inactivation of sodium during the action potential.

Answer 2

Sodium influx causes further sodium channels to open in a small initial window of positive feedback called prolonged depolarisation.

The depolarisation eventually causes a spontaneous snapping shut of the sodium channels in a process called sodium inactivation.

Question 3

Explain the difference between resistive and capacitative transmembrane current.

Answer 3

Resistive = ions flowing through the channels

Capacitative = ions approaching the membrane one side which expels ions on the other side

Question 4

What does myelination mean?

Answer 4

It means the nerve is insulated by myelin

Question 5

What are the gaps in the myelin sheath called?

Answer 5

Nodes of Ranvier

Question 6

What type of conduction is seen in myelinated nerve?

Answer 6

Saltatory conduction

Question 7

What does myelination do to conduction velocity?

How does it do this?

Answer 7

It increases it by:

1) increasing the diameter of the the axon, thereby decreasing the resistance it encounters
2) creates a lower membrane capacitance as charge can not be stored at the membrane due to the myelin meaning more is available to be utilised for conduction