nerves?

hello, i just had a quick question for anybody who may know. my moms cat (breed unknown) acts crazy when we scratch a certain part on her back. when just normlly petting this part of her back she acts odd as well. its right behind the middle of her back...when scratched or pet, she tilts her head to the side and meows, then proceeds to vigorously lick and or chew the upper part of one of her front legs. she doesnt run away, and when we stop she will stick around, excited for more petting. does she like this or is she in pain or discomfort with this spot? id think that if she didnt like it she would go away instead of sticking around for more. my mother insists she hates it, but i dont think so. my mother thinks its something to do with her nerves and she thinks the cat is becoming a nervous wreck when this happens lol. please tell me whats up. thanks my mom also thinks that the cat is scared of me and thats why she comes to me, that dosent make sense does it? if the cat was afraid she would stay away right??

There is a spot on their back right by their tail that they LOVE to have scratched,petted.I don't know why, but I've read several posts here saying that their cat loves it.Maybe it's a spot that they themselves can't scratch?
If the cat didn't like you, it would NOT come to you.It would shy away every time you were near it and run,hiss, or swat at you.

Well... here's a thought, for what it's worth: I myself have noticed that being brushed or tickled in a certain spot causes me to feel a tingle in some other remote spot, and it's always the same places resonating with each other. Maybe cats have these neural links, too?

Is the cat spayed? I doubt if it has any correlation but my cat does this same thing when I pet her back while she's in heat. It could just be a spot that she can't get herself like crittermom mentioned