Lecture 71 - Pathophysiology of Pain Flashcards
CLASSIFICATION OF PAIN
acute: injury, post-operative flare
chronic: pain lasts >3 months - nociceptive (inflammatory), neuropathic, visceral (inflammatory), mixed
Appropriate pain assessment and adequate pain management are considered to be standard of care, with pain being considered the “fifth vital sign”
FUNCTIONS OF PAIN
Warning system (avoid injury)
Aid in repair (hypersensitivity)
Can be maladaptive (e.g. irreversible neuropathy)
CHARACTERIZATION OF PAIN
Temporal features: Onset, duration, course, pattern
Intensity: Average, least, worst, current pain
Location: Focal, multifocal, generalized, referred, superficial, deep - Opioid induced hyperalgesia (generalized)
Quality: Inflammatory: throbbing, pulsating (inflammatory); Neuropathic: stabbing, shooting, burning, tingling; Visceral: squeezing
CLINICAL PAIN ASSESSMENT
Pain scale: Adult and children
Subjective: Abused by drug addicts
Pain is an emotion and impacts mood
Pain Transmission
Starts with peripheral stimulus (trauma, damage, inflammation) –> conducted to spinal cord where signal is processed and we get activation of CNS –> signal sent through ascending input to the brain for processing (central effect) –> info sent back down through descending modulation back to spinal cord
PERIPHERAL RECEPTORS AND CHANNELS INVOLVED IN PAIN SIGNALING
Temperature sensitive: Transient receptor potential cation channel (TRP); TRPV (Vanniloid) = Heat; TRPM (Melastatin) = cold
Acid sensitive: Acid sensing ion channel (ASIC) - Activated by H+, Conduct Na+
Chemical irritant sensitive: Histamine; Bradykinin
REFLEX UPON PAINFUL STIMULI
bypasses CNS, goes right back to muscle; signal doesn’t need to go to brain for processing
afferent nerve carries signal into spinal cord, sent to the muscle so body can move from source of pain
NERVE TRANSMISSION FROM PERIPHERY TO THE SPINAL CORD INVOLVES MANY DIFFERENT ION CHANNELS
Na+ channels important for conduction of pain signals along axon; conduct the action potential
THREE DIFFERENT PAIN FIBERS TRANSDUCE DIFFERENT PAIN SIGNALS
Abeta fibers
adelta fibers
C fibers
Abeta fibers
§ Non-noxious: Touch, pressure
§ Innervate the skin
§ Faster, (35-75 m/s)
Adelta fibers
§ Pain, cold
§ Myelinated
§ Fast (2-35 m/s)
§ “First pain”, reflex arc - Sharp, prickly
C-fibers
§ Pain, Temp, Touch, pressure, Itch (polymodal)
§ Unmyelinated
§ Slow (0.5-2 m/s)
§ “Second pain” - dull, aching
PERIPHERAL SENSITIZATION – SUBSTANCE P PLAYS AN IMPORTANT ROLE IN HEIGHTENING PAIN RESPONDING
Repeated stimuli reduces firing threshold; allows area to have more heightened pain response
Substance P
1. Vasodilation
2. Degranulation of mast cells
3. Release of histamine
4. Inflammation and prostaglandins
Increase expression of pain receptors - Sensitization
NEUROPATHIC PAIN SENSITIZATION
Possibly enhanced expression of sodium channel subtypes contributing to
* enhanced cellular excitability
* generation of ectopic action potentials
Increased AMPA and NMDA Expression and sensitivity
High expression of _____ receptors in the brain stem along the descending pathway
opioid