Pain Flashcards
What is hyperalgesia
overexperience of pain
Allodynia
experience of pain to a normal sensation (sunburn)
Hyperesthesia
magnification of sensory stimulus
Dysethesia
magnification or abnormal sensation
neuropathic pain
generated by nervous system rather than other tissue
Difference between nociceptive and neuropathic pain?
Nociceptive pain–Pain directly related to nociceptor
Neuropathic pain–Pain generated by nervous system
What stimulates nociceptive receptors?
Usually high threshold mechanoreceptors
Also some chemical receptors including tissue metabolites, neuromodulators, tissue cell products, and inflammatory mediators.
These mediators can activate/sensitize fibers, cause release of other substances, or cause inflammatory response to affect pain. others phosphorylate ion channels to change sensitivity to pain.
Note that when there is intense stimulation of pain fibers, they may release inflammatory chemicals from CNS and periphery
Adelta pain fibers
fast pain fibers. Indicates presence of pain
c pain fibers
Slow pain fibers unmyelinated. Gives sense of intensity of signal.
Depending on stimulus, pain fibers will release different transmitters. Examples include:
BDNF, Glu, SP
After stimulation of pain, where does the pain travel?
Through the zone of lissauer and distribute over 4-6 segments of the spinal cord. enter through the dorsal horn
Where do Ad/C fibers synapse?
C=Synapse in layer 1/4/5 of dorsal horn. More pain, more input and firing.
What are wide dynamic range cells? (WDR)
C fiber neurons. They fire more with more pain to signal the intensity of the pain. They receive input from many areas. Joints, back muscles, and legs can send information to a single WDR. Does not give highly localized information because of CONVERGENCE.
What causes referred pain?
convergence of wide dynamic range cells
What are the pain pathways?
- neospinothalamic tract
- paleospinothalamic tract
- spinoreticulothalamic tract
- propriospinal tract
neospinothalamic pathway
spinothalamic tract. carries C pain fibers
periaqueductal gray
Important for pain suppression
Intense pain fiber stimulation results in activation of:
enkephalin interneurons. Activate opiate receptors. early decrease in pain shortly after injury.
How is pain modulated?
Ab fibers (normal sensory) can inhibit pain systems through inhibitory glycine and or GABA neurons
What do descending pain systems release?
serotonin and norepinephrine. Synapse directly on the Wide Dynamic Range neurons.
thus, we have DESCENDING control over pain! treatments will boost serotonin and NE transmission
Describe the origin of the pathway of descending pain control systems
periaqueductal gray
Prominent opiate activity
What are mechanisms of pain control?
serotonin activation
norepinephrine activation
a2d subunit of voltage gated calcium channel
fast sodium channel modification
what is the role of the thalamus in pain?
Pain increases activity and blood flow in the thalamus. In chronic pain, blood flow decreases
Can pain activate short or long term potentiation?
yes. Phosphorylation of receptors increases short term sensitivity.
CA sets off intracellular events that change sensitivity to pain. HFS causes the release of neurotrophic factors. Increased synaptic conductivity as a result. Pain produces memory!
