Porth's Essentials of Pathophysiology, 4e

ensory mechanisms provide individuals with a con- tinuous stream of information about their bodies, the outside world, and the interactions between the two. The somatosensory component of the nervous system provides an awareness of pain, touch, temperature, and position, as compared to the specialized senses of sight and hearing (discussed in Chapter 38). Between 2 and 3 million nerve endings in the skin and deep body tis- sues provide a steady stream of encoded somatosensory information to the central nervous system. Only a small portion of this information reaches awareness; most of which provides input essential for the myriad of reflexes and automatic mechanisms that keep us functioning. This chapter is organized into two distinct parts. The first part describes the organization and control of somatosensory function, and the second focuses on pain as a somatosensory modality. The somatosensory system provides the central nervous system (CNS) with information related to deep and superficial body structures. It includes three types of neu- rons that vary in terms of distribution and type of sensa- tion that is detected—general somatic, special somatic, and general visceral. General somatic afferent neurons have branches with widespread distribution throughout the body and with many distinct types of receptors that result in sensations such as pain, touch, and temperature. Special somatic afferent neurons have receptors located primarily in muscles, tendons, and joints. These recep- tors sense position and movement of the body. General visceral afferent neurons have receptors in various visceral structures that sense fullness and discomfort. Somatosensory Systems Sensory systems can be conceptualized as a series of first-order, second-order, and third-order neurons. First- order neurons transmit sensory information from the Somatosensory Function, Pain, and Headache 35 C h a p t e r Organization and Control of Somatosensory Function S

Organization and Control of Somatosensory Function Somatosensory Systems The Sensory Unit Dermatomal Pattern of Innervation Spinal Circuitry and Ascending Neural Pathways Central Processing of Somatosensory Information Somatosensory Modalities Tactile Sensation Thermal Sensation Position Sense Pain Sensation Pain Theories Pain Mechanisms and Pathways

Pain Receptors and Primary Afferent Pathways Spinal Cord Circuitry and Ascending Pathways Brain Centers and Pain Perception

Central Pathways for Pain Modulation Endogenous Analgesic Mechanisms Types of Pain Cutaneous and Deep Somatic Pain

Visceral Pain Referred Pain Acute and Chronic Pain

Pain Management Assessment Nonpharmacologic Interventions Pharmacologic Treatment Surgical Interventions Alterations in Pain Sensitivity and Special Types of Pain Alterations in Pain Sensitivity Special Types of Pain Neuropathic Pain Neuralgia Complex Regional Pain Syndrome Phantom Limb Pain Headache and Associated Pain Headache Migraine Headache Cluster Headache

Tension-Type Headache Chronic Daily Headache Temporomandibular Joint Pain Pain in Children and Older Adults Pain in Children Pain Assessment Pain Management Pain in Older Adults Pain Assessment Pain Management

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