Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 18 Somatosensory Function, Pain, and Headache

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins The Somatosensory Component of the Nervous System Function –Provides an awareness of body sensations such as touch, temperature, limb position, and pain Composition –The sensory receptors consist of discrete nerve endings in the skin and other body tissues.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Four Major Modalities of Sensory Experience Discriminative touch Temperature sensation Body position Nociperception (pain sensation)

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Types of Neurons Found in Sensory Systems First-Order Neurons –Transmit sensory information from the periphery to the CNS Second-Order Neurons –Communicate with various reflex networks and sensory pathways in the spinal cord and travel directly to the thalamus Third-Order Neurons –Relay information from the thalamus to the cerebral cortex

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Sensory Neurons in the Spinal Track Dorsal root ganglion –All somatosensory information from the limbs and trunk shares a common class of sensory neurons The cell body of the dorsal root ganglion neuron, its peripheral branch, and its central axon form what is called a sensory unit

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Pathways from the Spinal Cord to the Thalamic Level of Sensation The Discriminative Pathway –Crosses at the base of the medulla and the anterolateral pathway –Relays information to the brain for perception, arousal, and motor control The Anterolateral Pathways –Consist of bilateral multisynaptic slow-conducting tracts –Provide for transmission of sensory information that does not require discrete localization of the signal source or fine discrimination of intensity

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which pathway is used for perception, arousal, and motor control? –A. The anterolateral pathways –B. The discriminative pathways

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer B. The discriminative pathways Rationale: The discriminative pathways relay information to the brain for perception, arousal, and motor control.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Processing Sensory Modalities Receptors Adequate stimuli Ascending pathways Central integrative mechanisms

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Central Processing of Pain Information Transmission to the somatosensory cortex –Pain information is perceived and interpreted. The limbic system –Emotional components of pain are experienced. Brain stem centers –Autonomic nervous system responses are recruited.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Clinical Assessment of Somatosensory Function Diagnostic analysis of the level and extent of damage in spinal cord lesions involves –Testing of the ipsilateral dorsal column (discriminative touch) system. –Testing of the contralateral temperature projection systems.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Theories Explaining the Basis for Pain Specificity Theory –Pain as a separate sensory modality evoked by the activity of specific receptors that transmit information to pain centers in the forebrain Pattern Theory –Pain receptors share endings or pathways with other sensory modalities. –Different patterns of activity of the same neurons can be used to signal painful and nonpainful stimuli.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Theories Explaining the Basis for Pain (cont.) Gate Control Theory –The presence of neural gating mechanisms at the segmental spinal cord level accounts for interactions between pain and other sensory modalities. Neuromatrix –The brain contains a widely distributed neural network, called the body–self neuromatrix, that contains somatosensory, limbic, and thalamocortical components that work together to create the individual neural patterns.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Symptoms of Tissue and Nerve Injury Allodynia –Pain from noninjurious stimuli to the skin Hyperalgesia –Extreme sensitivity to pain Analgesia –The absence of pain from stimuli that normally would be painful

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Types of Pain Nociceptive Pain –Nociceptors (pain receptors) are activated in response to actual or impending tissue injury. Neuropathic Pain –Arises from direct injury to nerves

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Mechanisms of Pain First-Order Neurons –Detect stimuli that threaten the integrity of innervated tissues Second-Order Neurons –Process nociceptive information Third-Order Neurons –Project pain information to the brain Nociceptors Aδ Fibers –Fast pain C Fibers –Slow wave pain

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Transmission of Pain Neospinothalamic tract –Provides for rapid transmission of sensory information to the thalamus –Transmission of sharp–fast pain information to the thalamus Pain is experienced as bright, sharp, or stabbing in nature. –Synapses are made; the pathways continue to the contralateral parietal somatosensory area to provide the precise location of the pain. Paleospinothalamic tract –Slow-conducting tracts that transmit sensory signals that do not require discrete localization or discrimination of fine gradations in intensity –Projects into the intralaminar nuclei of the thalamus –Diffuse, dull, aching, and unpleasant sensations that commonly are associated with chronic and visceral pain

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Transmission of Pain (cont.) Opioid peptides –Enkephalins –Endorphins –Dynorphins Endogenous analgesic center in the midbrain Pontine noradrenergic neurons The nucleus raphe magnus in the medulla send inhibitory signals to dorsal horn neurons in the spinal cord.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Pain Threshold and Tolerance Pain Threshold –The point at which a stimulus is perceived as painful Pain Tolerance –The maximum intensity or duration of pain that a person is willing to endure before the person wants something done about the pain

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Acute Versus Chronic Pain Acute Pain –Self-limiting pain that lasts less than 6 months Chronic Pain –Persistent pain that lasts longer than 6 months –Lacks the autonomic and somatic responses associated with acute pain –Is accompanied by debilitating responses

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Types of Pain Cutaneous –Sharp, burning pain –Origin in skin or subcutaneous tissues Deep –More diffuse and throbbing –Origin in body structures

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Types of Pain (cont.) Visceral –Diffuse and poorly defined –Results from stretching, distention, or ischemia of tissues Referred –Originates at a visceral site but perceived as originating in part of the body wall that is innervated by neurons entering the same segment of the nervous system

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which type of pain is perceived as sharp and intense? –A. Cutaneous –B. Visceral –C. Referred –D. Deep

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer A. Cutaneous Rationale: Cutaneous is a sharp, defined pain that originates in the skin or subcutaneous tissue.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Assessments of Pain Nature Severity Location Radiation Methods have been developed for quantifying a person’s pain based on the patient’s report. –Verbal descriptor –Numeric pain intensity –Visual analog

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Nonpharmacologic Interventions for Pain Cognitive–behavioral –Relaxation –Distraction –Imagery –Biofeedback Physical agents –Heat and cold Stimulus-induced analgesia Acupuncture and acupressure

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Pharmacologic Treatment of Pain Nonnarcotic analgesics –Nonsteroidal anti-inflammatory drugs (NSAIDs) –Antiseizure medications –Antidepressants Opioid analgesics –Morphine congeners

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Painful Sensations Allodynia Hyperalgesia Hyperesthesia Paresthesias Hyperpathia Analgesia Hypoalgesia Hypoesthesia

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Pain and Pain Syndromes Neuropathic pain –Originates from pathology Trigeminal neuralgia –Facial tics or spasms and characterized by paroxysmal attacks of stabbing pain Postherpetic neuralgia –Pain of shingles/herpes infection Complex regional pain syndrome –Autonomic and vasomotor instability

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Phantom Limb Pain Type of neurologic pain Follows amputation of a limb or part of a limb As many as 70% of amputees experience phantom pain. The pain often begins as sensations of tingling, heat and cold, or heaviness, followed by burning, cramping, or shooting pain.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins International Headache Society Classification of Headaches Primary headaches Headaches secondary to other medical conditions Cranial neuralgias and facial pain

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Types of Headaches Migraine headache Tension-type headache Cluster headache Chronic daily headache Temporomandibular joint syndrome

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Categories of Migraine Headaches Types of Migraines –Migraine without aura –Migraine with aura Subtypes of Migraine –Ophthalmoplegic migraine –Hemiplegic migraine –Aphasic migraine –Retinal migraine

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Treatment of Headaches Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) are effective in controlling pain because they block the enzyme needed for prostaglandin synthesis. Nonpharmacologic treatment of migraines includes the avoidance of migraine triggers, such as foods or smells that precipitate an attack. Pharmacologic treatment of migraines involves both abortive therapy for acute attacks and preventive therapy.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which of the following is associated with grinding of teeth? –A. Tension-type headache –B. Cluster headache –C. Chronic daily headache –D. Temporomandibular joint syndrome

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer D. Temporomandibular joint syndrome Rationale: Temporomandibular joint syndrome is brought about by clenching and grinding of the teeth, usually while sleeping.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Pain in Children and Elderly Misperceptions of pain in children and adults by caregivers Infants –Pain pathways, cortical and subcortical centers, and neurochemical responses associated with pain transmission are developed and functional by the last trimester of pregnancy. –May be attenuated due to underdeveloped pathways For infants and noncommunicating children, physiological symptoms must be used for assessment. Children can self-report pain.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Pain in Children and Elderly (cont.) Research is inconsistent about whether there are age- related changes in pain perception. Some apparent age-related differences in pain may be due to differences in willingness to report the pain rather than actual differences in pain. Assessment ability varies greatly with the mental state of patient.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Pain Treatment in Children Children experience and remember pain, and even fairly young children are able to accurately and reliably report their pain. Recognition of this has changed the clinical practice of health professionals involved in the assessment of children’s pain. Pharmacologic (including opioids) and nonpharmacologic pain management interventions have been shown to be effective in children. Nonpharmacologic techniques must be based on the developmental level of the child and should be taught to both children and parents.

Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Pain Treatment for the Elderly When prescribing pharmacologic and nonpharmacologic methods of pain management for the older population, care must be taken to consider the cause of the pain, the person’s health status, the concurrent therapies, and the person’s mental status. In the older population, where the risk of adverse events is higher, the nonpharmacologic options are usually less costly and cause fewer side effects.