Last updated: Thu, Jun 22, 2017
Cells in the dorsal horn fire a prolonged burst of impulses after they receive a brief input volley from sensory nerves. This after-discharge becomes more and more extended if they receive a sequence of excitations from C fibers at a rate between one each half second and five per second. After a few seconds of this, the wind-up of sensitivity halts. This process is perceived as a temporal summation.
It is thought that this is biologically functional, and that the increase in action potentials promotes defensive responses to harm.