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Pain
An unpleasant sensory AND emotional experience associated w/ actual or potential tissue damage
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Nociception
- The neural process of encoding noxious stimuli
- Consequences of encoding may be autonomic (i.e. elevated BP) or behavioral (motor withdrawal)
- *Pain sensation is not necessarily implied
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Noxious Stimulus
A stimulus that is damaging or threatens damage to normal tissues
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Sensitization
Increased responsiveness of nociceptive neurons to their normal input and/or recruitment of a response to normally sub-threshold inputs
Central Sensitization: increased responsiveness of nociceptive neurons in the CNS to their normal or sub-threshold afferent input
Peripheral Sensitization: increased responsiveness and reduced threshold of nociceptive neurons in the periphery to the stimulation of their receptive fields
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Acute Pain
- Short duration w/ sudden onset
- Easily diagnosed/treated/resolved
- At/near site of lesion (if referred, in typical referral patterns)
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Chronic Pain
- Starts 3-6 months after injury (lasts 6 months or longer)
- Difficult to diagnose/identify specific cause for pain
- Referred far from site of lesion/atypical referral patterns
- Emergence of illness behaviors not always a physiological sign of warning for the body
- May be related to physiological changes in the nervous system (reduced thresholds, neurotransmitter imbalance, psychological factors, not an identifiable injury)
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Chronic Pain: Common Features
- Substance abuse/overuse
- Multiple procedures/surgeries
- External locus of control
- Vegetative signs
- Physical, emotional, sexual abuse
- Exaggerated clinical presentation (verbal or nonverbal pain behavior)
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Factors Influencing Pain Perception and Behavior
- Personality
- Social Context
- Culture
- Attitudes of Health Professionals
- Past Experience
- State of Mind
- Avoidance and Cognitive Processes
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Medical Model of Pain Management
- Assumes an underlying injury
- Remove/alleviate/fix the injury and the pain will go away
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Behavioral/Cognitive Behavioral Model
- Pain perception due to more than just the injury (psychological state, physiological changes in long standing pain states)
- History of depression --> reduced pain thresholds
- Chronic pain state: receptor sensitivity is heightened
- Treating the inure alone won't address pain perception
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Somatosensory Receptors
- A Delta:
- Small, myelinated
- Speed = mod fast
- Location = capsules, ligaments, fat, blood vessels, connective tissue
- Stimuli = mechanical, thermal
- Sensation = sharp, prickling sensation, small areas (increased stimulation --> habituation)
- C Polymodal
- Small, unmyelinated
- Speed = slow
- Location = capsules, ligaments, fat, blood vessels, connective tissue
- Stimuli = mechanical, thermal, chemical
- Sensation = dull aching sensation over larger areas (increased stimulation --> sensitization)
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Dorsal Horn
- Marginal Zone (I)
- Substantia Gelatinosa (II)
- Nucleus Proprius (III-VI)
"Soup at the dorsal horn" = combination of facility and inhibitory transmitters (mix determines transmission)
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Intermediate
Intermediate Gray Matter (VII - VIII)
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Anterior/Ventral Horn
Anterior Horn Cells (IX)
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Chemical Stimulants of Nociceptors
- Protons (H+, acids)
- Neurotransmitters (serotonin, histamine, ACh)
- Polypeptides (bradykinin, kallidin)
- Prostaglandins
- Cellular metabolites (ATP, ADP, lactic acid, K+)
- Spicy plants (capsaicin)
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Neurotransmitters of Primary Afferent
- Substance P
- Vasoactive Intestinal Peptide (VIP)
- Cholecystokinin
- Somatostatin
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Biomedical Model
One-to-one relationship between the magnitude of the injure and the pain experience (mind and body = distinct entities)
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Biopsychosocial Approach
- Treatment aimed at changing behavior
- Pain = unreliable guide
- Education regarding maladaptive pain = paramount
- Graded exercise gradually acclimates the pt to function
- Focus on slow, progressive functional recovery
- Empower the patient
- Use of narcotic pain meds can undermine this process
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