Why, when my leg/arm/any limb “goes to sleep” does it hurt once the feeling starts coming back to, but if I am given a numbing agent, it doesn’t hurt when the feeling comes back?

Question

So, when you fall asleep leaning on your arm and roll over, it starts to hurt as the feeling comes back. But if you go to the dentist and they numb your mouth, it doesn’t hurt once that starts coming back?

In: Biology

Answer 1

Because when leaning on your arm, you were most likely squishing your nerves and veins. Doing this causes the blood vessels to constrict, and the nerves begin to “turn off” due to lack of blood supply. When the blood comes back, they begin firing again, and the “pins and needles” sensations is each individual nerve turning back on again, and sending the “SOMETHING BAD HAPPENED” signal. When you go to the dentist, the numbing agent doesn’t “turn off” your nerve cells, the cells are still on and are actually trying to tell your brain that there is pain, but the numbing agent works by interfering with a part of your nerves where the “SOMETHING BAD IS HAPPENING” signal is intercepted and prevented from traveling to your brain. This is why as the numbing agent wears off, you don’t get that “pins and needles” feeling, just the left-over ache from whatever the dentist was doing in your mouth.