Pain Disorders Flashcards
Epicritic pain. (Also describe threshold)
This is pain that is identified with well-defined and discriminative qualities
Shows low threshold but accurate localization
Protopathic pain (and threshold)
This is emotion-laden pain of a chronic nature with poorly defined qualities
Shows high threshold but poor localization
Which type of pain is less responsive to opioid therapy?
epicritic pain
What do nociceptors sense? (Obviously pain but what triggers the response)
allow awareness of tissue injury
Where are nociceptors found?
in all tissues except the brain
Fast pain travels in unmyelinated or myelinated fibers?
myelinated
Describe fast pain.
sharp, localized, stabbing pain perceived with injury; sharp pain, pricking pain, acute pain, and electric pain
Slow pain (how it presents) (unmyelinated or myelinated fibers)
longer lasting dull diffuse pain traveling in unmyelinated fibers.
What type of chemicals stimulate pain fibers in the viscera?
bradykinin, histamine, prostaglandin
Each nociceptive receptor subtype is mediated by one or more members of what ion channel family?
TRP-Vanilloid ion channel family
Receptor for extreme heat is mediated by what ion channel family?
Vanilloid family
What fiber type carries sharp, pricking pain>
A (delta)
What fiber type carries slow burning and sharp, pricking pain?
A (delta)
What fiber group carries hot, burning sensation, extreme cold and crude touch?
C fibers (unmyelinated)
PG increases sensitivity of pain terminals to which chemicals?
bradykinins and other pain producing substances
What does substance P do?
vasodilation, neurogenic edema and BK release
also causes Histamine (H) release from mast cells; and 5HT from platelets
Mechanisms of action of neuropathic pain.
Following injury, increased sensitization of nociceptive afferents and terminals causes impulse generation in absence of stimulation
Induced by
Local increase conc. of Na+ channels
Epinephrine sensitivity
What are the 2 broad groups by which central pain pathways are grouped?
neospinothalamic pathway
paleospinothalamic pathway
What senses does the neospinothalamic pathway mediate?
Pathway mediates conscious awareness of well-defined pain (epicritic pain) & temperature sensations
Another name for the paleospinothalamic pathway?
anterior spinothalamic pathway
Describe the path from DRG to 3rd order neurons of General Paleospinothalamic pathway.
1st order in DRG
2nd order in dorsal horn
cross the midline
3rd order projects to midline and intralaminar thalamic nuclei
Ends in cerebral cortex especially the cingulate gyrus
What sensations does the paleospinothalamic pathway mediate?
Pathway mediates arousal and integration of pain sensations with diverse learned behavioral/ emotional responses
Describe path of spino-reticulo-thalamo-cortical pathway.
1st order: DRG
2nd order terminate on medullary and pontine ARAS
3rd order: fibers from ARAS project to midline and intralaminar thalamic nuclei
then project diffusely to cerebral cortex
Fibers from ARAS also project directly to cerebral cortex
What senses does the spino-reticulo-thalamo-cortical pathway mediate?
Pathway probably mediates integration of painful stimuli with alertness; fly or fight response
What is the spino-mesencephalo-limbic pathway route?
1st order: DRG
2nd order: dorsal horn terminate in PAG of midbrain level
3rd: PAG at midbrain level and project to amygdala via parabrachial nuclei of pons
PAG also projects downstream to dorsal horn via raphe nuclei of brainstem
What sensation does the spino-mesencephalo-limbic pathway mediate?
pain modulation
integration of painful stimuli with fear, rage and related autonomic and homeostatic responses
Regarding pain modulation from the periphery….
Large cutaneous afferent terminals for pain modulation contain what type of fibers? (Where do they synapse)
A Beta fibers
which synapse on enkephalin-mediating interneurons in dorsal horn of spinal cord
explain pain reduction while rubbing area of skin around painful stimuli
Pain modulation from central structures.
Be able to explain pain modulation (pain reduction) via PAG.
- PAG projects to nucleus raphe magnus (NRM) in rostral medulla
- NRM (5-HT mediated) in turn projects to enkephalin-mediating (EK) interneurons in dorsal horn of spinal cord.
- EK neurons in turn inhibit pain fibers pre-synaptically and 2nd order pain neurons post synaptically.
Pain modulation from central structures.
Describe the noradrenergic pathway of pain modulation from the brain. (pain reduction
- NE containing nuclei in rostral Pons (locus ceruleus) descend to spinal levels to synapse on enkephalin-mediating (EK) interneurons in dorsal spinal cord.
- EK neurons in turn inhibit pain fibers pre-synaptically and 2nd order pain neurons post synaptically.
- Process results in pain reduction
Describe how rubbing a sore on the arm reduces pain through spinal gating.
descending analgesic fibers from reticular formation travel down reticulospinal tract to dorsal horn
- secrete inhibitory substances that block
pain fibers from secreting substance P
- pain signals never ascend
dorsal horn fibers inhibited by input from mechanoreceptors
Glutamate and substance P pain modulation. (Where exactly released)
is released at axonal terminals of pain afferents in spinal cord
Where are opiate receptors present?
are present on pre-synaptic axonal terminals of pain fibers terminating in spinal cord as well as on dendrites of 2nd order neurons in pain pathway
Enkephalin is released where?
released from terminals of enkephalinergic inhibitory interneurons located in dorsal horn
What does EK act on and how does in modulate pain?
EK acts on pre-synaptic opiate receptors on pain afferents to reduce Ca+ entry and decrease glutamate and substance P release at afferent pain terminals.
EK also acts post-synaptically on opiate receptors on 2nd order pain neurons, hyperpolarizes the neurons through increased K+ conductance and attenuates effects of nociceptive stimuli
Serotonin and NE from Nucleus raphe medullaris (NRM) and Nucleus Locus Ceruleus (NLC) respectively excite what type of neurons located in dorsal horn of spinal cord to facilitate their actions?
EK inhibitory neurons
Lesions of the neospinothalamic tract in the spinal cord, will cause what to happen?
Contralateral loss of pain and temperature from one or two segments below level of lesion down and throughout the rest of the body.
Lesions of the lateral division of the dorsal root that mediate pain afferents to the spinal cord, will cause what to happen?
Ipsilateral loss of pain and temperature at affected spinal segmental level(s)
Ipsilateral loss of nociceptive induced spinal segmental reflexes at affected levels (e.g. loss of flexor withdrawal reflex)
Lesions of the neospinothalamic tract in the brainstem and thalamus will cause what to happen?
Contralateral hemi-anesthesia (loss of pain) and temperature in the body relative to the lesion
Hyperalgesia
Enhancement of pain sensation
An exaggerated response due to excessive excitation of pain pathway
In particular what happens to receptors which precipitates hyperalgesia?
sensitization of nociceptors
What are the causes of hyperalgesia?
excessive sensitivity of Pain receptor ( primary hyperalgesia) and
facilitation of sensory transmission( secondary hyperalgesia) in spinal
cord and thalamus
What is a known substance causing nociceptor sensitization?
Prostaglandin E2
Describe phantom limb pain.
Describes pain felt by an amputee from missing limb
Over-activity of 2nd order pain-mediating neurons in spinal cord of amputated side creates false feeling of pain
Describe thalamic pain.
Lesion in Ventral Posterior Lateral nucleus of thalamus especially involving terminals of DCML
Chronic, excruciating pain occurs in response to non-noxious stimuli on the body.
Pain is not ameliorated by standard pain relievers
How does one treat thalamic pain?
Relief is mainly through use of antiepileptics and/or surgical intervention
Neuralgia
Describes severe and persistent pain in distribution of a cranial or spinal nerve, e.g. Trigeminal neuralgia, TN, Post-herpetic neuralgia, etc.
Trigeminal neuralgia is usually characterized by what and not responsive to what?
Episodic stabbing pain in distribution of CN5
Non-responsiveness to standard pain relievers
How would one treat trigeminal neuralgia?
Relief is usually through surgical intervention; e.g. alcohol injection of trigeminal nerve, or carefully placed lesion to damage descending spinal tract of V in dorsolateral medulla or SCA decompression
Referred pain. (Also what is a name for it?)
Describes pain arising from deep visceral structures that is felt at sites on body surface
Also called misinterpreted pain and reflective pain
Mechanism of action of referred pain.
Convergence of nociceptive and general cutaneous afferents from same spinal segment on same 2nd order dorsal horn cells is advanced to explain phenomenon
What type of pain is characteristic of higher centers incorrectly ascribe pain sensation to emanate from skin rather than deep visceral structure?
refered pain
What is another name for referred pain?
reflective pain aka misinterpreted pain
Allodynia
Describes condition of painful response to stimuli that would not normally cause pain.
MOA of allodynia
Dysfunction in pain modulation due to misalignment of interaction between mechanoceptive and nociceptive pathways and
Molecular level sensitization of CNS neurons in the pain pathway
What are some complications of Chronic pain syndrome?
Depressed mood, fatigue, sleep disorders
Reduced activity, dependent behavior
Alcohol and other substance abuse
What are Steinbach’s 6 D’s of somatization?
Dramatization of complaints, Dysfunction/Disuse, Dependency, Depression, Disability and Drug misuse
Waddell’s sign?
may indicate non-organic or psychological component to chronic low back pain. Historically they have also been used to detect malingeringin patients with back pain.
