How are impulses propagated along an axon?

The axon is polarised at rest. This means that there is a negative charge within the axon and a positive charge outside. This resting polarisation is caused by a Na/K pump that uses active transport to transport 3 Na+ ions out of the axon in exchange for two K+ ions entering the axon. This means that more positive ions are outside the axon causing an electrochemical gradient. When an impulse is generated, the change in charge causes Na+ voltage gated channels to open and Na+ ions to rush into the axon down their electrochemical gradient. This means the once polarised axon becomes depolarised and this is an action potential. This change in charge in this section of the axon causes voltage gated Na+ channels to open on the next section of the axon and this whole process begins again. This happens in a domino-like fashion so that an action potential propagates itself along an axon.