Nociception

Nociception

Pain is possibly the most unpleasant sensations our senses can detect. Even though we typically fail to remember what pain feels like when we are not experiencing it, we certainly do not wish to experience pain. Despite pain's unpleasantness, it has to be appreciated for what it is. Namely, a mechanism that allows us to avoid dangerous situations, to prevent further damage, and to promote the healing process. Pain allows us to remove ourselves form dangerous situations, as we attempt to move away from noxious stimuli that cause pain. As we attempt to escape stimuli that cause pain after an initial insult on our body, pain can prevent further damage form occurring. Finally, pain promotes the healing process as we take great care to protect an injured body part form further damage as to minimize the experience of more pain. How is this unpleasant, yet helpful sensation detected?

Nociception is the term commonly used to refer to the perception of pain. The receptors involved in pain detection are aptly enough referred to as nociceptors - receptors for noxious stimuli. (1) These nociceptors are free nerve endings that terminate just below the skin as to detect cutaneous pain. Nociceptors are also located in tendons and joints, for detection of somatic pain and in body organs to detect visceral pain. Pain receptors are very numerous in then skin, hence pain detection here is well defined and the source of pain can be easily localized. In tendons, joints, and body organs the pain receptors are fewer. The source of pain therefore is not readily localized. Apparently, the number of nociceptors also influences the duration of the pain felt. Cutaneous pain typically is of short duration, but may be reactivated upon new impacts, while somatic and visceral pain is of longer duration. (2) It is important to note that almost all body tissue is equipped with nociceptors. (1, 2) As explained above, this is an important fact, as pain has primary warning functions. If we did not feel pain and if pain did not impinge on our well-being, we would not seek help when our body aches. Hence, it makes evolutionary sense for the body to be so well equipped with nociceptors in almost all locations. The most notable exception to this logic is the brain. The brain itself has no nociceptors and therefore is pain insensitive. Why is this all-important structure not equipped with and therefore indirectly protected by nociceptors?