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Following completion of this chapter, the student will be able to:


  • Compare the various types of pain and appraise their positive and negative effects.
  • Choose a technique for assessing pain.
  • Analyze the characteristics of sensory receptors.
  • Examine how the nervous system relays information about painful stimuli.
  • Distinguish between the different neurophysiologic mechanisms for pain control for the therapeutic modalities used by clinicians.
  • Predict how pain perception can be modified by cognitive factors.


The International Association for the Study of Pain defines pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.”1 Pain is a subjective sensation with more than one dimension and an abundance of descriptors of its qualities and characteristics. In spite of its universality, pain is composed of a variety of human discomforts, rather than being a single entity.2 The perception of pain can be subjectively modified by past experiences and expectations.37 Much of what we do to treat patients' pain is to change their perceptions of pain.3


Pain does have a purpose. It warns us that something is wrong and can provoke a withdrawal response to avoid further injury. It also results in muscle spasm and guards or protects the injured part. Pain, however, can persist after it is no longer useful. It can become a means of enhancing disability and inhibiting efforts to rehabilitate the patient.4 Prolonged spasm, which leads to circulatory deficiency, muscle atrophy, disuse habits, and conscious or unconscious guarding, may lead to a severe loss of function.5 Chronic pain may become a disease state in itself. Often lacking an identifiable cause, chronic pain can totally disable a patient.


Research in recent years has led to a better understanding of pain and pain relief. This research also has raised new questions, while leaving many unanswered. We now have better explanations for the analgesic properties of the physical agents we use, as well as a better understanding of the psychology of pain. Newer physical agents, such as laser, and recent improvements to older agents such as diathermy and transcutaneous electrical nerve simulators offer new approaches to the treatment of musculoskeletal injury and pain.6 The evolution of the treatment of pain is, however, incomplete. Not even the mechanisms for the analgesic response to the simplest therapeutic modalities, heat and cold, have been fully described.7


The control of pain is an essential aspect of caring for an injured patient. The clinician can choose from several therapeutic agents with analgesic properties.8 The selection of a therapeutic agent should be based on a sound understanding of its physical properties and physiologic effects. This chapter will not provide a complete explanation of neurophysiology, pain, and pain relief. Several physiology textbooks provide extensive discussions of human neurophysiology and neurobiology to supplement this chapter. Instead, this chapter presents an overview of some theories ...

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