Are there missions in Starcraft 2 that prevent you from playing others?

With the exception of the missions that explicitly give you a choice and make it obvious that one mission will prevent another (specifically, not different missions, just different objectives/rewards etc) are there any missions that, by choosing to embark on them, prevent you from performing other missions? Without giving away any spoilers, there is specifically one instance I can think of in the campaign where I could see this happening, but it was never explicitly stated that choosing one mission over the other would create a permanent fork in the story line.

Does anybody know for sure (or perhaps know what I'm referencing)?

Thanks! Chris

There is one mission like that in the final few missions that give you an option between 2 missions and depending on what you choose it makes the next mission change a bit, but it is still the same mission.

There is also one hidden objective in one of the missions that will give you access to a secret mission that can only be played by completing this objective, this mission however is not crucial to the story.