Physiology and Pathophysiology of Pain Flashcards
what is the 1st step of processing pain?
Periphery:
Detection
Transmission to spinal cord (first order neurons)
what is the 2nd step of processing pain?
Spinal cord:
Processing
Transmission to brain (Thalamus) (second order neurons)
what is the 3rd step of processing pain?
Brain:
Perception, learning, response
what is the 4th step of processing pain?
Modulation:
Descending tracts
What is nociception?
The detection of tissue damage by specialized transducers connected to A-delta and C fibers
what are nociceptors?
Free nerve endings of A delta and C-fibres
Respond to thermal, chemical, mechanical noxious stimuli
describe Primary afferents?
Cell body in Dorsal root ganglion
First order neurons
Synapse at spinal cord
what are the 4 different types of Primary afferents?
Aα fibres
Aβ fibres
Aδ fibers
C fibres
what neurones receive the input from Rexed lamina 2 and 5?
Nociceptive specific
Low Threshold Mechanoceptive
Wide Dynamic Range
where does the Spinothalamic tract arise in?
Rexed Lamina 2 & 5
what is the Spinothalamic tract ?
Major ascending tract for nociception
sending impulses to thalamus
what is the second relay station in the brain?
thalamus
where does the Lateral Spinothalamic Tract terminate?
Ventroposterior thalamic nuclei
The medial thalamic nuclei receives input from where?
ventral spinothalamic tract
where does the Ventroposterior thalamic nuclei project to?
somatosensory cortex
where does the medial thalamic nuclei project to?
Cortex
Limbic system
where does Pain perception occur?
somatosensory cortex
what is the primary control center for descending pain modulation?
Periaqeductal grey
describe the defending pathways of pain modulation?
from brain to dorsal horn
Usually decreases pain signal
Noradrenergic system
what is hyperalgesia?
abnormally heightened sensitivity to pain
happens whenever there is tissue injury and inflammation.
what is allodynia?
Decreased threshold for response
what is Spontaneous Pain?
Spontaneous activity in nerve fibres
what is Central sensitization?
It is the response of second order neurons in the CNS to normal input both noxious & non-noxious
what are the three main components of Central sensitization?
wind-up
classical
long-term potentiation
what is the main difference between Central sensitization and peripheral sensitization?
central sensitization happens at the level of spinal cord and acts in tandem.
what is wind-up Central sensitization?
Involves only activated synapses
Homosynaptic activity dependent progressive increase in response of the neurons
Manifests over the course of stimuli & terminates with stimuli
what is Classical Central sensitization?
Involves opening up of new synapses (silent nociceptors)
Heterosynaptic activity dependent plasticity
Immediate onset with appropriate stimuli
Outlast the initial stimuli duration
Can be maintained even at low levels of ongoing stimuli
what is Long-term potentiation
Involves mainly the activated synapses
Occurs primarily for very intense stimuli
what is acute pain?
<1 month Physiological Presence of noxious stimuli Serves protective function Usually nociceptive
what is chronic pain?
Pain for 3–6 months or more Pathological Presence of noxious Does not serve any purpose Nociceptive, neuropathic or mixed
What is nociceptive pain?
A sensory experience that occurs when specific peripheral sensory neurones (nociceptors) respond to noxious stimuli
What is neuropathic pain?
Pain initiated or caused by a primary lesion or dysfunction in the somato-sensory nervous system
describe nociceptive pain
Pain typically localised at the site of injury – often described as throbbing, aching or stiffness
Usually time limited and resolves when damaged tissue heals
Can be chronic
Tends to respond to analgesics
describe neuropathic pain
pain occurs in the neurological territory of the affected structure (nerve, root, spinal cord, brain)
Almost always a chronic condition (e.g. postherpetic neuralgia [PHN], poststroke pain)
Responds poorly to analgesics
what are some examples of neuropathic pain?
postherpetic neuralgia [PHN]
poststroke pain
what drugs are effective when transduction is affected structure?
NSAIDs
Ice
Rest
LA blocks
what drugs are effective when transmission is affected structure?
Nerve blocks
Drugs
Opioids
Anticonvulsants
Surgery
DREZ
Cordotomywhat drugs are effective when Perception is affected structure?
Education Cognitive behavioural therapy Distraction Relaxation Graded motor imagery Mirror box therapy
what drugs are effective when Descending modulation is affected structure?
Placebos
Drugs
Opioids
Antidepressants
Surgery
Spinal cord stimulation
