Chapter 8: Sensory Processing, Touch & Pain

Sensory Processing, Touch & Pain begins by establishing how sensory receptor organs function as filters for environmental energy, utilizing mechanisms of sensory transduction to convert stimuli into electrical receptor potentials and action potentials. The text explains the concept of labeled lines to differentiate sensory modalities and explores how stimulus intensity and location are encoded through neural firing rates and receptive fields with center-surround organization. Key concepts such as sensory adaptation—distinguishing between rapid-adapting phasic receptors and slow-adapting tonic receptors—and top-down processing are defined. The summary details the anatomy and physiology of touch, categorizing skin receptors including Pacinian corpuscles (vibration), Meissner’s corpuscles (light touch), Merkel’s discs (fine details), and Ruffini’s endings (stretch), noting the role of Piezo2 ion channels. It traces the dorsal column system, explaining how tactile information ascends through the medulla and thalamus to the primary somatosensory cortex (S1), and discusses the plasticity of cortical maps in response to experience or limb loss. A significant portion of the chapter is dedicated to nociception, identifying free nerve endings and specific receptor proteins like TRPV1, TRPM3, and CMR1 that detect heat, cold, and chemical irritants like capsaicin. The transmission of pain via myelinated A-delta fibers (fast pain) and unmyelinated C fibers (slow pain) through the anterolateral (spinothalamic) system is contrasted with touch pathways. Finally, the description covers complex pain phenomena, including neuropathic pain, phantom limb sensations, and the role of the anterior cingulate cortex in processing the emotional aspects of both physical pain and social rejection, concluding with pain modulation strategies involving the periaqueductal gray, the gate control theory, endogenous opioids, and cannabinoids.