How do we perceive sensations?

I know that we feel by way of our nerves, and they send signals to the brain which tell it what we are feeling, whether it be pain, pleasure, motion, texture, surroundings, etc. What I want to know is what exactly happens at the nerve ending. How does it "feel" in the first place? Specifically, are there any mathematical ratios that it picks up, and are there mathematical ratios for pleasure, most importantly, but also are there mathematical ratios for pain or textures, also?