Physiology and pathophysiology of pain Flashcards
What is pain?
Unpleasant sensory and emotional experience which we primarily associate with tissue damage or describe in terms of such damage or both
What does the periphery do in the pain pathway?
Detect stimulus
transmission to spinal cord - 1st order neuron
What does the spinal cord do in the pain pathway?
process
transmission to brain (thalamus) - 2nd order neuron
What does the brain do in the pain pathway?
perception, learning and response
What part of the pain pathway modulates the pain?
descending tracts
What is nociception?
The detection of tissue damage by specialised transducers connected to A delta and C fibres
What are nociceptors?
Free nerve endings of A delta and C fibres which respond to thermal, chemical, mechanical noxious stimuli
Where are 1st order neurons cell body and where do they synapse?
DRG
spinal cord
4 types of afferent sensory fibres
A alpha, A beta, A delta and C
What are the 3 kinds of neurons which receive input in the spinal dorsal horn?
nociceptive specific
low threshold mechanoreceptor
wide dynamic range
What are the 2 types of spinothalamic tratcs?
Anterior and lateral
Where does spinothalamic tract arise (which rexed lamina)?
2,5
Where does the lateral STT terminate?
ventroposterior thalamic nuclei
Where does the anterior STT terminate?
medial thalamus
Connections of the thalamus
cortex
limbic system
brain stem
Where does pain perception occur?
somatosensory cortex
Why is the limbic system important?
make memory of event
add emotional component
Where do descending pathways travel from and what is the major part?
brain to dorsal horn
periaqueductal grey
What type of system is the descending pathway?
noradrenergic
What is hyperalgesia?
Increased perception of pain or even perception of non-noxious stimuli as noxious stimuli
When does hyperalgesia occur?
Whenever there is tissue injury and inflammation
Where does primary and secondary analgesia occur?
primary - site of injury
secondary - surrounding uninjured tissue
What is alodynia?
A form of hyperalgesia
Dynamical mechanical hyperalgesia to light touch for example
Changes in nociceptor in allodynia
Decreased threshold for response
Changes in nociceptor in hyperalgesia?
Exaggerated response to normal and supranormal stimuli
Changes in nociceptor in spontaneous pain
Spontaneous activity in nerve fibres
3 main components of central sensitisation
wind up
classical
long term potentiation
What is central sensitisation?
The response of second order neurons in the CNS to normal input both noxious and non noxious
Briefly describe wind-up
Involves only activated synapses and starts and terminates with stimulus and progressively increases
Briefly describe classical central sensitisation
opening up new silent synapses and starts with stimuli and can outlast the termination
Long term potentiation - briefly describe
Involves mainly activated synapses
occurs primarily in very intense stimuli
How long does chronic pain last?
3-6 months
Briefly describe acute pain eg tissue damage, pain, protection
Physiological and usually nociceptive
obvious tissue damage, protective, pain resolves after healing
Briefly describe chronic pain eg tissue damage, pain, protection
pathological with no protective function which degrades health
can be nociceptive or neuropathic pain or mixed
What is nociceptive pain?
A sensory experience that occurs when specific peripheral sensory neurons respond to noxious stimuli
Does nociceptive or neuropathic pain usually respond to conventional analgesics?
nociceptive
What is neuropathic pain?
Pain initiated or caused by a primary lesion or dysfunction in the somato-sensory nervous system
Transduction treatments
NSAIDS, ice, rest, LA blocks
Transmission treatments
nerve blocks, surgery, drugs eg opoids, anticonvulsants
Perception treatments
Education, CBT, relaxation, distraction, mirror box therapy
Descending modulation treatments
Placebos, drugs eg opoids, antidepressants, surgery, spinal cord stimulation
