Physiology and Pathophysiology of Pain Flashcards
What is pain?
An unpleasant sensory and emotional experience which we primarily associate with tissue damage
What is step 1 in the pain pathway?
Detection in the periphery: transmission to the spinal cord by 1st order neurons
What is step 2 in the pain pathway?
Processing in the spinal cord: transmission to the thalamus by 2nd order neurons
What is step 3 in the pain pathway?
Perception, learning and response
What is step 4 in the pain pathway?
Modulation: descending tracts
What is nociception?
The detection of tissue damage by specialized transducers connected to A-delta and C fibers
Which stimuli do nociceptors responds to?
Thermal, chemical, mechanical and noxious stimuli
Where do 1st order neurons synapse and where do they have their cell bodies?
Cell body in dorsal root ganglion
Synapse at spinal cord
What fibres do the lateral spinothalamic tracts carry?
Fast and slow pain
What fibres do the anterior spinothalamic tracts carry?
Simple touch sensation
Where does the spinothalamic tract arise?
Rexed lamina 2 & 5
What is the function of the thalamus?
Secondary relay station
Where does pain perception occur?
Somatosensory cortex
What is hyperalgesia?
Increased perception of pain or perception of non-noxious stimuli as noxious stimuli
What is allodynia?
hyperalgesia to light touch
What changes to the nociceptor are seen in allodynia?
Decreased threshold for response
What changes to the nociceptor are seen in hyperalgesia?
Exaggerated response to normal and supranormal stimuli
What changes to the nociceptor are seen in spontaneous pain?
Spontaneous activity in nerve fibres
What are the characteristics of acute pain?
<1 month, obvious tissue damage, increases nervous system activity, pain resolves upon healing and is protective
What are the characteristics of chronic pain?
Pain for more than 3 months, beyond the expected healing period, with no protective function and which degrades health and function
What is nociceptive pain?
A sensory experience that occurs when specific peripheral sensory neurones respond to noxious stimuli
What are the characteristics of nociceptive pain?
Painful region is localised to site of injury, usually time limited/resolves when damaged tissue heals (can be chronic) and tends to respond to conventional analgesics
What is neuropathic pain?
Pain initiated or caused by a primary lesion or dysfunction in the somato-sensory nervous system
What are the characteristics of neuropathic pain?
Painful region may not be the site of injury, almost always chronic and responds poorly to conventional analgesics
Which therapies affect the transduction of pain?
NSAIDS, ice, rest and LA blocks
Which therapies affect the transmission of pain?
Nerve blocks, drugs (opioids and anticonvulsants) and surgery (DREZ and cordotomy)
Which therapies affect the perception of pain?
Education, cognitive behavioural therapy, distraction, relaxation, graded motor imagery and mirror box therapy
Which therapies affect the descending modulation of pain?
Placebos, drugs (opioids and antidepressants) and surgery (spinal cord stimulation)
