What is the meaning of the division of the Quran into Surahs?

If I understand correctly, the Quran is held to be the words given to Mohammed by God over a series of visits from the angel Gabriel, which were then dictated to scribes and eventually written down. * Why is the Quran divided into the 114 surahs? * Does each surah represent a single revelation to Mohammed by God, that is, a single visit from the angel Gabriel, and the words of the surah are simply a direct transcription of what the angel Gabriel said? * Or, is the organization into surah "man-made", something that came later?