"you have to be ready to really let loose."

That can be very dangerous to your voice!

Well, I suppose I should have added the caveat, "Don't hurt yourself!" I suppose that what Ron was getting at in advising that you try singing along with the way-high-pitched Beach Boys, but not with the even more remarkably stratospheric Four Seasons. But I won't take back my assertion that timidity and excessive constraint will make any kind of vocal-range breakthrough impossible.

I still contend that it IS possible to extend one's "natural range," although it may often involve violating the principles of formal classical vocal training. We just heard mention of an obvious option ~ falsetto ~ that extends your range out of the "natural" realm into a wholly different approach that is, in some sense, "unnatural." Also mentioned was the problem/potential of making the transition from "normal" to falsetto and back again; you can try to mask or smooth over that transition or, on the other hand, emphasize it (as in yodeling, or in the style of Professor Longhair).

I don't know that there are names for them, but there are other "voices," other techniques besides falsetto that extend vocal range by changing the way you use your vocal apparatus (mouth, throat, vocal cords, etc.) I can hit some pretty low bass notes by singing from a lower part of my torso and a deeper area of my throat than I use for my normal baritone/tenor range, and up at the high end, there's a "blues-shouting" approach very common in soul/R&B singing that allows a higher reach into the upper octaves, somehow without sounding as "feminine" or soprano-like as the falsetto technique.