Lecture 71 - Pathophysiology of Pain

Question 1

CLASSIFICATION OF PAIN

Answer 1

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”

Question 2

FUNCTIONS OF PAIN

Answer 2

Warning system (avoid injury)
Aid in repair (hypersensitivity)
Can be maladaptive (e.g. irreversible neuropathy)

Question 3

CHARACTERIZATION OF PAIN

Answer 3

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

Question 4

CLINICAL PAIN ASSESSMENT

Answer 4

Pain scale: Adult and children
Subjective: Abused by drug addicts
Pain is an emotion and impacts mood

Question 5

Pain Transmission

Answer 5

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

Question 6

PERIPHERAL RECEPTORS AND CHANNELS INVOLVED IN PAIN SIGNALING

Answer 6

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

Question 7

REFLEX UPON PAINFUL STIMULI

Answer 7

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

Question 8

NERVE TRANSMISSION FROM PERIPHERY TO THE SPINAL CORD INVOLVES MANY DIFFERENT ION CHANNELS

Answer 8

Na+ channels important for conduction of pain signals along axon; conduct the action potential

Question 9

THREE DIFFERENT PAIN FIBERS TRANSDUCE DIFFERENT PAIN SIGNALS

Answer 9

Abeta fibers
adelta fibers
C fibers

Question 10

Abeta fibers

Answer 10

§ Non-noxious: Touch, pressure
§ Innervate the skin
§ Faster, (35-75 m/s)

Question 11

Adelta fibers

Answer 11

§ Pain, cold
§ Myelinated
§ Fast (2-35 m/s)
§ “First pain”, reflex arc - Sharp, prickly

Question 12

C-fibers

Answer 12

§ Pain, Temp, Touch, pressure, Itch (polymodal)
§ Unmyelinated
§ Slow (0.5-2 m/s)
§ “Second pain” - dull, aching

Question 13

PERIPHERAL SENSITIZATION – SUBSTANCE P PLAYS AN IMPORTANT ROLE IN HEIGHTENING PAIN RESPONDING

Answer 13

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

Question 14

NEUROPATHIC PAIN SENSITIZATION

Answer 14

Possibly enhanced expression of sodium channel subtypes contributing to
* enhanced cellular excitability
* generation of ectopic action potentials
Increased AMPA and NMDA Expression and sensitivity

Question 15

High expression of _____ receptors in the brain stem along the descending pathway

Answer 15

opioid