What can cause Chronic Pain?
Chronic pain is primarily due to a condition called hyperalgesia, or heightened sensitivity to a stimulus that would not normally be painful. Pain sensing neurons (called nociceptors) in the peripheral tissues express cation channels, called Transient Receptor Potential (TRP) channels, that open in response to noxious stimuli, contributing to the generation of an action potential, and the transmission of a pain signal to the spinal cord. At their terminals in the spinal cord, these neurons release glutamate which activates second-order neurons that carry the signal to pain centers in the brain. The spinal cord is a major site of opioid action, where mu-opioid receptors inhibit the release of glutamate.