Skip to Main Content


  • Pain is a subjective, unpleasant, sensory, and emotional experience associated with actual or potential tissue damage or abnormal functioning of nerves. It may be classified as acute, chronic, or cancer pain.



  • Nociceptive (eg, from touching something too hot, too cold, or sharp) and inflammatory pain (eg, trauma or surgery) are both adaptive and protective.

  • The steps in processing pain are:

    • ✓ Transduction—stimulation of nociceptors.

      • ❖ Nociceptors found in both somatic and visceral structures, are activated by mechanical, thermal, and chemical stimuli. Noxious stimuli may cause release of cytokines and chemokines that sensitize and/or activate nociceptors.

    • ✓ Conduction—Receptor activation leads to action potentials that continue along afferent fibers to the spinal cord. Stimulation of large-diameter, sparsely myelinated fibers evokes sharp, well-localized pain. Stimulation of small-diameter, unmyelinated fibers produces aching, poorly localized pain.

    • ✓ Transmission—Afferent nociceptive fibers synapse in the spinal cord’s dorsal horn, releasing excitatory neurotransmitters (eg, glutamate and substance P). The spinothalamic tract and other pathways bring the signal to the brain’s higher cortical structures.

    • ✓ Perception—The experience of pain occurs when signals reach higher cortical structures. Relaxation, meditation, and distraction can lessen pain, and anxiety and depression can worsen pain.

    • ✓ Modulation—Possible modulating factors include glutamate, substance P, endogenous opioids, γ-aminobutyric acid (GABA), norepinephrine, and serotonin.

  • The interface between neurons and immune cells in the central nervous system (CNS) may facilitate maintenance of chronic pain.


  • Pathophysiologic pain (eg, postherpetic neuralgia, diabetic neuropathy, fibromyalgia, irritable bowel syndrome, and chronic headaches) is often described as chronic pain. It results from damage or abnormal functioning of nerves in the CNS or peripheral nervous system (PNS). Pain circuits sometimes rewire themselves anatomically and biochemically, resulting in chronic pain, hyperalgesia, or allodynia.



  • Patients may be in acute distress or display no noticeable suffering.


  • Acute pain can be sharp or dull, burning, shock-like, tingling, shooting, radiating, fluctuating in intensity, varying in location, and occurring in a temporal relationship with an obvious noxious stimulus. Chronic pain can present similarly and often occurs without a temporal relationship to a noxious stimulus. Over time, the chronic pain presentation may change (eg, sharp to dull).


  • Acute pain can cause hypertension, tachycardia, diaphoresis, mydriasis, and pallor. These signs are seldom present in chronic pain. In chronic noncancer pain, depression, sleep disturbances, anxiety, and employment and family instability tend to dominate.

  • In acute pain, outcomes of treatment are generally predictable. In chronic pain, comorbid conditions are often present, and treatment outcomes are often unpredictable. For chronic noncancer pain, an interdisciplinary approach (eg, pain clinic) is preferred.


  • Pain is always subjective; thus pain is ...

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.