Passage of an action potential

Question 1

Passage of action potential along unmyelinated axon (process)

Answer 1

Axon membrane is polarised, greater conc of positive ions outside axon than inside
Stimulus causes sudden influx of Na+ and depolarisation occurs, causing an action potential.
Localised electrical currents caused by influx of Na+ ions causes the opening of voltage gated channels further along the axon, causing this region to experience influx of sodium ions and thus depolarisation.
Behind this region, Na+ voltage gated protein channels and begin to close while the K+ voltage gates begin to open, initiating repolarisation.
The action potential is propogated along the axon while the axon area behind the action potential has returned back to resting potential.
Repolarisation of the axon means Na+ can be actively transported out to be ready for new stimuli.

Question 2

How is an action potential passed along a myelinated sheath?

Answer 2

Action potentials occur at the nodes of Ranvier
Myelin acts as alectrical insulator, preventing action potentials forming between nodes of Ranvier
Localised circuits therefore arise between adjacent nodes of Ranvier around the myelin
This is called saltatory conduction

Question 3

Why is action potential conducted fast in myelinated sheath than unmyelinated?

Answer 3

In myelinated sheath, depolarisation doesnt not have to occur across the entire length of the axon, only at the nodes of Ranvier.