Transmission of Pain Signals by the Brain at the Spinal Level
Pain has been defined by Coates & Hindle as an unpleasant emotional and sensory experience which signals a potential or actual damage to tissues (2011, p. 213). Pain is a common human experience and can emanate from injury and illness. There are two main types of pain; acute pain is short-lived, lasting for minutes or several days and its onset often takes place rapidly. It results from the activation of pain nerve endings or nociceptors either by internal or external pain stimuli. On the other hand chronic pain is continuous and sometimes recurrent and can last for weeks, months or even years. Chronic pain is usually not located at or related to the tissue undergoing trauma (Draper & Knight, 2007, p. 104). Various theories have been proposed to explain the mechanism underlying the transmission and perception of pain.
These include the specificity theory which maintains that specific fibers and pain receptors are activated by injury after which the pain signals are projected via the spinal pathway to an area in the brain that interprets the pain. In this regard, the specificity theory virtually equates the peripheral injury with the psychological experience caused by the pain (Anderson, 2004, p. 355). However, this theory has been found to harbor several limitations as research about pain has intensified with time. In light of this, the gate theory that was proposed by Melzack and Wall has had a major contribution to the understanding of pain transmission and perception (Pain Game Part 2, 2011). Research has demonstrated that pain is affected by psychological and physiological factors which helps to explain the mechanism underlying inhibition and/or facilitaion of pain signal at the spinal level. This paper discusses these factors in light of the mechanism underlying transmission and regulation of pain signals.
Since its proposition in 1965, the gate control theory has made major contributions particularly in the understanding of how the brain inhibits or facilitates transmission of pain signals at the spinal level. This is because of the fact that the gate control theory lays emphasis on the central nervous system which is made up of the brain and spinal cord as opposed to the peripheral nervous system. The theory is based on several propositions. The first proposition is that a gating mechanism located at the dorsal horn of the spinal cord modulates nerve impulse transmission from afferent fibers to the transmission cells of the spinal cord (Anderson, 2004, p. 355).
The second proposition is that depending on the relative level of activity of small-diameter and large diameter fibers, the gating mechanism will be influenced differently. In this regard, activity in small-diameter fibers tend to facilitate transmission of pain signals or to open the gate whereas large fiber activity tends to inhibit transmission or close the gate. The gate control theory also suggests that there is...