Principles & Practice of Pain Medicine > Part I. Pain: Biology, Anatomy, and Physiology > Chapter 1. Molecular Biology of Pain Tony L. Yaksh

Overview

"The acute activation of small sensory afferent axons by high-intensity thermal and mechanical stimuli evokes locally organized spinal motor reflexes (nociceptive reflexes), autonomic responses, and pain behavior in animals and humans. This effect is mediated by the local encoding of afferent input at the level of the dorsal horn and the activation of spinofugal projection neurons. These projection systems travel both ipsilaterally and contralaterally in the ventrolateral aspect of the spinal cord, projecting supraspinally into the medulla, mesencephalon, and diencephalon. Medullary projections serve to activate spinobulbospinal reflexes that influence autonomic tone. Other projections into the mesencephalon and thalamus are assumed to contribute to the perceptual and complex emotive and discriminative components of the pain state. It is important to appreciate that the encoding by the sensory afferent and the spinal dorsal horn of the nociceptive stimulus is the first step in nociceptive processing, and this encoding process contributes properties that are important to the understanding of the behavioral correlates of nociception. The following sections consider aspects of the mechanisms whereby injury leads to an ongoing pain state from the perspective of the organization of the sensory afferents and the spinal dorsal horn. Of particular importance is the appreciation that these linkages have distinct pharmacologies and that these systems can be regulated to display prominent increases (hyperalgesia) and decreases (analgesia) in the input-output functi..."