Last updated: Sun, Jun 18, 2017
If you now press or poke in the area of injury, you will find that a press which would not have hurt before the injury now does hurt. This is called primary hyperalgesia. It is the result of increased sensitivity of the neurons in the area of the injury. The neuron fires more rapidly for the same level of stimulation, or it fires at the same rate for a lower level of stimulation. Two local mechanisms account for primary hyperalgesia. First, nociceptors become sensitized when they are fired. Second, the chemicals of inflammation raise their level of excitation or can actually cause them to fire spontaneously, without any further stimulation. Some neurons that are normally insensitive to mechanical stimulation become sensitive during inflammation.