Pathophysiology of pain Flashcards
Describe step 1 in the pain pathway
Periphery - detection, transmission to spinal cord
Describe step 2 in the pain pathway
Spinal Cord - procession, transmission to the brain
Describe step 3 in the pain pathway
Brain - perception, learning, response
Describe step 4 in the pain pathway
Modulation -descending tracts
What fibres are involved in noceception?
A-delta and C fibres
What do nociceptors respond to?
Thermal, chemical, mechanical noxious stimuli
Where do nociceptive fibres synapse?
DRG in spinal cord
What is the function of the thalamus?
To act as a second relay station
Name a function of the descending pathways
To decrease the pain signal
Where do descending pathways arise from?
The dorsal horn
Describe the affect allodynia has on the nociceptor?
central pain sensitisation following non-painful, repetitive stimulation resulting in pain response from a stimulus which usually does not cause pain
Describe the affect that hyperalgesia has on the nociceptor?
Exaggerated response to normal and supranormal stimuli
Describe central sensitisation
condition of the nervous system that is associated with the development and maintenance of chronic pain. Occurs at level of spinal cord and is the response of second order neurons in CNS to both noxious and non-noxious stimuli
Describe wind up
A pathological change that lowers the threshold for pain signals to be transmitted. Caused by repeated stimulation of C fibres
Descrbe classical central sensitisation
Involves opening of new synapses in dorsal horn which recieve input and record nociception. Signal has to be intense enough to elicit a response. Response is immediate and might outlast duration of stimulus
Describe long term potentiation
Persistent strengthening of synapses based on recent patterns of activity resulting in long lasting transmission signal increase between two neurones. Only occurs in active neurones and for very intense stimuli
Describe the characteristics of acute pain?
Usually obvious tissue damage, increased nervous system activity, pain resolves upon healing, serves as a protective function
Describe the characteristics of chronic pain?
> 3-6 months, pain beyond expected period of healing, usually has no protective function, degrades health and function
What is nociceptive pain?
A sensory experience that occurs when specific peripheral sensory neurones respond to noxious stimuli
Describe features of nociceptive pain?
Pain region is typically localised at site of injury, usually time limited and resolves when damaged tissue heals, can also be chronic, tends to respond to conventional analgesics
What is neuropathic pain?
pain initiated or caused by a primary lesion or dysfunction in the somato-sensoty nervous system
What are features of neuropathic pain?
The painful region may not necessarily be the same as the site of injury- pain occurs in the neurological territory of the affected structure, almost always in a chronic condition, responds poorly to conventional analgesics
What may cure pain from the transduction pathway?
NSAIDs, Ice, Rest, LA block
What may cure pain from the transmission pathway?
Nerve blocks, Drugs, Surgery
What may cure pain from the perception pathway?
Education, CBT, Distraction, Relaxation, Graded Motor Imagery, Mirror Box Therapy
What may cure pain from the descending modulation pathway?
Placebos, Drugs, Surgery
What are primary afferents?
Cell body is in DRG, they synapse at spinal cord
Where does pain perception occur?
The somatosensory cortex
Describe the ascending pain pathway
Prostaglandins is released in response to inflammation and sensory nerves respond to this by projecting to the dorsal horn of spinal cord.
1st order neurons synapse at spinal cord and relay pain signals to second order neurons
2nd order neurons decussate at spinal cord and pass into spinothalamic tract, where they project up into thalamus
2nd order neurones synapse onto third order neurons which help discern area of injury
Site of injury is contralateral to side of brain receiving information about pain
Describe the descending pain pathway
Aim is to modulate pain
First order neurons arise from periaqueductal grey matter and synapse in medulla.
Second order neurones are seritonergic / noradrenergic and project into the dorsal horn of spinal cord. They inhibit first order neurons from the ascending pain pathway from synapsing with second order neurons.
Substance P is also inhibited
Hemisection of the spinal cord results in what?
CONTRALATERAL loss of pain and temperature below lesion (as spinothalamic tract decussates at the spinal cord)
IPSILATERAL loss of touch (as DCML decussates at medulla)
IPSILATERAL spasticity and loss of motor function (as CST decussates at medulla)
