by mtoom

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What is pain?
Unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.
What is chronic/neuropathic pain?
Pain that persists longer than the temporal course of natural healing, associated with a particular type of injury or disease process.
What are the types of pain?
  • Provide 3 categories and 4 types of pain
Superficial pain
  • Sharp, pricking pain
    -myelinated Aδ fibers
    -mechanical or temperature related pain
  • Dull, burning pain
    -unmyelinated C fibers
    -responds to a broad range of painful stimuli, including mechanical, thermal or chemical factors
Deep/visceral pain
  • unmyelinated C fibers
  • arises from joints, muscles, connective tissue
  • causes skeletal muscle contraction
Referred pain
  • mediated by unmyelinated C fibers
  • pain perceived at site adjacent to or at a distance from the site of injury's origin
  • Which fibers can localize pain better?
  • What receptors increase the localization of pain?
  • Aδ fibers localize pain far better than C fibers
  • Tactile receptors help to localize pain (when touch is felt in addition to pain)
Pain can be divided into what two categories with regard to its usefulness/adaptiveness?
  • Adaptive
  • Maladaptive
What are 2 types of adaptive pain?
  • What are they adaptive?
  • Nociceptive (caused by a noxious stimulus)
  • Inflammatory (promotes healing by preventing contact with injury)
  • What is hyperalgesia?
  • What is allodynia?
  • Hyperalgesia: Increased reponse to a normally painful stimuli
  • Allodynia: Painful response to a normally benign stimulus
What are two types of maladaptive pain?
  • Neuropathic: Pain that occurs in response to damage to the nervous system
  • Functional: Pain that occurs in resposne to abnormal operation of the nervous system
Give 2 causes of neuropathic pain
  • Shingles
    -Paintful blisters
  • Post-herpetic neuralgia
    -Nerve damaged caused by virus
    -Described as burning, stabbing, or gnawing
Give 1 cause of functional pain
  • Medically unexplained syndrome with no cure or universally accepted treatment
  • Characterized by chronic widespread pain and allodynia
  • Muscle and connective tissue pain
  • What are the 2 mechanisms of hypersensitivity?
  • What is meant by "sensitivity" in this context?
  • Peripheral sensitization
  • Central sensitization
Sensitivity: Increase in the excitability of neurons
  • What is peripheral sensitization?
  • It occurs primarily why?
  • Reduction in threshold, and an increase in responsiveness of the nociceptors
  • Occurs due to action of inflammatory chemicals or mediators released around the site of tissue damage
What are 2 common inflammatory chemicals responsible for peripheral sensitization?
  • 5-HT (serotonin)
  • Kinins
How do inflammatory chemicals cause peripheral sensitization?
By altering excitabitability of nociceptive receptors, which alters the excitability of the neuron
What are the 2 processes that affect peripheral sensitivity?
Post-translation processing
  • Phosphorylating receptors
  • Lowers threshold at which receptors open
  • Making channels open for longer
Altered transcription
  • Signals transported back to cell body to alter transcription
  • Increased protein
  • Protein shipped back to terminal to increase responsiveness
What is central sensitization?
Increase in excitability of neurons within the central nervous system so that normal inputs begin to produce abnormal responses
  • Contributes to hyperresponsive conditions such as post-op pain, migraine, neuropathic pain, fibromyalgia, GI pain
How is pain normally transmitted in central nervous system?
  • Name 2 types of receptors
  • AMPA receptors activated by glutamate
  • NMDA receptors blocked by Mg2+
How does central sensitization occur following injury (acute phase)?
Summation of synaptic inputs from activation of nociceptors results in removal of Mg2+ from NMDA increasing sensitivity to glutamate, resulting in:
  • Receptors are phosphorylated
  • Increases recruitment of receptors to synaptic membrane
  • Enhances receptor kinetics
  • Decreases receptor threshold
  • Windup occurs
What is wind-up and what is the role in central sensitization?
Progressive increase in the discharge of dorsal horn neurons in response to repeated low-frequency activation of nociceptors
What are 4 changes that happen in the peristent phase of central sensitization?
  • Increased local gene expression of receptors
  • Increased global gene expression
  • Loss of inhibition of interneurons in spinal cord
  • Structural reorganization where Aβ fibers sprout and form novel synpases where atrophied C fibers were once connected
What is gate theory?
The idea that the transmission of pain through the spinal cord can be modulated by:
  • Other afferent neurons
  • Controls emanating from the brain
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