Update iPod command?

Is there a command which allows me to update my iPod?

For example:

1. Say my iPod is plugged to my iMac.
   
   
2. Then I buy a song from iTMS. My "Purchased" songs is synced ith my iPod.
   
   
3. However when I eject my iPod it hasn't updated - and the recently bought song has not been loaded onto my iPod.
   

So I'd like to know if there's a button/command that I can press/activate between steps 2 and 3, so that the song gets loaded onto my iPod.

At the moment the only workaround I have is to disconnect then immediately reconnect my iPod.

 

Thanks for the replies.