Chapter 14: Somatosensory Function, Pain & Temperature Regulation

Somatosensory Function, Pain & Temperature Regulation meticulously details the fundamental principles of somatosensory function, pain mechanisms, headache disorders, and body temperature regulation. Somatosensory pathways are organized using first-, second-, and third-order neurons, transmitting sensory information regarding touch, temperature, body position, and pain through distinct routes. Fine discrimination and proprioception rely on the rapid discriminative pathway, while crude touch and thermal sensations utilize the slower anterolateral pathway; information is centrally processed, crudely localized in the thalamus, and fully interpreted in the cerebral cortex, which is organized according to the sensory homunculus. The core concepts of pain are introduced through historical theories like Specificity and Gate Control, leading to the modern Neuromatrix theory, explaining how nociceptors activated by mechanical, thermal, or chemical stimuli transmit signals via fast Aδ and slow C nerve fibers. The discussion distinguishes types of pain—acute, chronic, visceral, and referred—and addresses complex pain syndromes, including various neuralgias and phantom limb pain. Effective management utilizes a combination of pharmacological agents, such as opioids and NSAIDs, alongside nonpharmacological methods like TENS and cognitive-behavioral techniques. Furthermore, the chapter categorizes and examines primary headache disorders, covering the specific etiologies, clinical features, and treatments for migraine, cluster, and tension-type headaches, as well as temporomandibular joint pain. Finally, the principles of thermoregulation are explored, defining core temperature homeostasis achieved through balancing heat production (metabolism, shivering) and heat loss (radiation, conduction, convection, evaporation). Pathological states are carefully differentiated: fever results from an upward adjustment of the hypothalamic set point due to pyrogens, while hyperthermia (including heatstroke and malignant hyperthermia) occurs when heat production overwhelms the body's natural cooling mechanisms, and hypothermia involves a dangerously low core temperature, presenting risks particularly in vulnerable populations like infants and older adults.