Somatosensation

Under normal circumstances, the somatosensory system contributes more to shaping movements than to perception. Yet damage to the somatosensory system can result in spontaneous pain and other abnormal somatic perceptions. An exploration of the mechanisms and pathways involved in touch perception is slanted toward understanding the contribution of the dorsal column–medial lemniscus pathway to the generation of paresthesia and dysesthesia. Peripheral somatosensory afferents that contribute to the perception of sharp or aching pain, temperature, and itch are described. The properties of transient receptor potential (TRP) channels on nociceptors and thermoreceptors are described. Physiological and pharmacological mechanisms that lead to neurogenic inflammation are considered. How peripheral and central changes triggered by acute injury or disease can lead to long-lasting changes that support chronic pain is described. Persistent pain that occurs independently of any stimulus is termed neuropathic. Mechanisms of referred pain from deep structures including viscera are introduced.