How to refresh a custom object when an opportunity is updated

Hi,
We have created a custom object and it consists of fields and pick lists that are mapped from the corresponding opportunity. At the moment, when the opportunity is edited, it doesn't update the custom object automatically and we have to go into it, open an editable field and save it for it to show the same information that was just entered in the opportunity.
Is there a way to to force the update of that custom object every time the opportunity is edited and saved?