Nerve Propagation: How do action potentials move along and axon?

Question 1

What are the charges and concentrations at resting potential in an axon?

Answer 1

Inside membrane: HIGH K+, Negative charge

Outside membrane: HIGH Na+, Posit. charge

Question 2

How is the first action potential (AP) created?

Answer 2

When stimulated, V-D Na+ channels open & Na+ flows into axon, depolarising membrane. Localised electric currents generated in the membrane.Na+ ions move into ADJACENT polarised (resting) region causing change in electrical charge (PD) across this part of membrane.

Question 3

How is the second action potential (AP) created?

Answer 3

Change in PD in membrane adjacent to 1st AP initiates a second AP. At site of 1st action potential, the V-D Na+ channels close and V-D K+ channels open. K+ leave axon repolarising mem.. Membrane becomes hyperpolarised.

Question 4

How is the third action potential (AP) created?

Answer 4

3rd AP initiated by 2nd AP. In this way, local electric currents cause the nerve impulse to move along the axon. At site of 1st AP, K+ ions diffuse back into axon, restoring resting potential.

Question 5

What is the refractory period?

Answer 5

A new AP can’t be generated in same section of mem. for 5 milisec. It lasts until all V-D Na+ and K+ channels have returned to normal resting state (closed) and resting potential normal.

Question 6

What is the benefit of having a refractory period?

Answer 6

It ensures that the impulse is unidirectional.