Social studies has to do alot with pictures about the past along with text. If you can see and remember the picture then the answers will come to mind. If you can remember that then you can remember other things by only a picture. If you practice it alot then you can get to the point where you could see it once and remember it for months.
I believe the answer is: activation of large nerve fibers in your spinal cord
Gate control theory was popularized by Ronald Melzack and Patrick Wall, it views that non-painful area input closes the doors or "gates" to the painful area input, this exist in order to prevents pain sensation from coming through the central nervous system and being transferred across our body.
