Higher rep ranges (7-12) will help to stimulate slow-twitch muscle fibers. They're small pink/red fibers, which don't grow as much, but will still give some results.
However, the real growth is in fast-twitch muscle fibers, using low rep ranges (6 and below).
40 reps is way too many, you'll really only get endurance from that, unless you're a newbie and are still making your year's worth of beginner gains.
I'd suggest checking the sticky (post at the top of this board) on Needsize's 5x5 Routine. It's an excellent routine, well-organized and proven to work, that targets both types of muscle fibers. Plus, it's quite simple. Check it out!