II. Pathophysiology

  1. Pain Perception Factors
    1. Response to Chronic Pain may be learned
    2. Reaction to pain may be reinforced (patient, family)
    3. Behavior may persist after pain resolves
  2. Modulation of sensation
    1. First dorsal horn Synapse enhances or inhibits pain
    2. Modulation occurs in various locations
      1. Spinothalamic Tract
      2. Frontal cortex
      3. Descending inhibitory neuro-systems
  3. Pain Mechanisms
    1. Neuropathic pain
      1. Characteristics: Burning, stabbing or shooting pain
      2. Examples: Stroke, Radiculopathy
    2. Musculoskeletal pain or Mechanical compression pain
      1. Characteristics: Aching, soreness, stiffness
      2. Examples: Myofascial Pain Syndrome, Fibromyalgia, Low Back Pain
    3. Inflammatory pain
      1. Characteristics: Aching, swelling, hot, red
      2. Examples: Rheumatoid Arthritis, Postoperative pain, Septic Joint
  4. Dorsal horn Synapse physiology
    1. Neurotrasmitters transmitting pain signals from C-polynodal Nociceptor (presynaptic)
      1. Glutamate
      2. Dense core vessicles contain Substance P, CGRI, CCK, BDNF
    2. Receptors on post-synaptic membrane of dorsal horn Neuron
      1. AMPA receptors (nociceptive pain)
        1. Responds to acute physiologic pain
        2. Bind glutamate
        3. Respond to morphine
      2. NK-1 and NMDA receptors
        1. Responds to chronic pathologic pain (non-nociceptive pain)
        2. Bind Substance P, CGRI, CCK, BDNF from dense core vessicles
        3. Poor response to morphine

III. Pathophysiology: Gate Control Theory

  1. Specific pain fibers from injured tissues via
    1. Alpha fibers myelinated
    2. Delta and C-fibers unmyelinated
    3. Modulated at spinal cord gate
      1. Substantia gelatinosa
      2. Control transmission cells
    4. Spinothalamic Tract cephalad
  2. Descending signals (regulate gate at spinal cord)
    1. Pain transmission can be blocked by emotion or mood
    2. Sensory discriminative system
      1. Determines differences in sensory threshold
    3. Motivational Affective System
      1. Reciprocal relationship between mood and pain
    4. Central control processes
      1. Include unknown processes of pain

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