Chronic Pain 2 Flashcards
What is sensitization?
Repeated or intense noxious stimulus causes changes in the SC and brain
- Lowers threshold for activation
- Amplifies subsequent inputs, even for benign stimuli
**Basically, the nervous system adapts and becomes over-effective where anything can cause a big rxn
Sensitization is adaptive. Why is this important?
- becomes hyper-alert to potentially damaging conditions
- The problem is that this is NO LONGER ABOUT PROTECTION
Sensitization produces these:
- Allodynia
- Hyperalgesia or hypersensitization
- Secondary hyperalgesia
Allodynia
Pain produced by a normally innocuous stimulus
Hyperalgesia or hypersensitization
- Exaggerated and prolonged response
- Primary hyperalgesia is part of a normal process. Secondary is NOT
Secondary hyperalgesia
- Spread beyond site of stimulation or injury
- Also known as “referred pain”
With peripheral sensitization, there is an increased responsiveness of:
- Nociceptors at area of injury
- greater sensitivity around injury area
With peripheral sensitization, the injury causes the release of
Sensitizing soup
What is sensitizing soup?
- neuropeptide cascade
- inflammatory process increases release of neuropeptides
Peripheral sensitization causes a reduction in
Threshold for nociceptors
Peripheral sensitization and DOMS
Get crazy pain with DOMS and trigger points
Peripheral sensitization mechanisms
brief (lasting days) muscle hyperalgesia
When does brief muscle hyperalgesia with peripheral sensitization?
- induced after eccentric exercise
- soreness after 1-2 days (DOMS)
- model for hyperalgesic trigger points
Central sensitization is the uncoupling of pain from
Peripheral stimuli
Synaptic transmission and central sensitization
Get changes to synaptic transmission to the SC
- membrane excitability
- synaptic recruitment
- decreased inhibition
Central sensitization: nociceptive pathways
- get novel inputs to nociceptive pathways
- activates A-beta large low threshold mechanoreceptor pathways
What is the functional shift that occurs with central sensitization?
High threshold mechanoreceptors now respond to low threshold input
What are the two mechanisms of central sensitization?
- enhancement
- changes in the brain
Some studies show that the PAG is (larger/smaller) in individuals with chronic pain
Smaller
In addition to central sensitization, PAG is linked with these problems
Depression in chronic pain
Central sensitization: enhancement
- increased membrane excitability in dorsal horn
- synaptic efficacy » neuronal plasticity
What are the changes in the brain that occur with central sensitization?
- Reduced inhibition of descending system
- Impaired motor control of spinal muscles
- Effect on dorsal horn neurons in SC
- Receptive field expansion
Reduced inhibition of descending system
Periaqueductal grey matter doesn’t inhibit pain as it should
PAG function
- blocks unnecessary information
- If not working, all info ends up in the cortex
