Central mechanisms of Pain Flashcards
what is the Localization and intensity of pain
the Sensation of pain
what is the Emotional response (Psychological component) of pain
Affective component
what is short term pain with an identifiable source
Acute
what is long term pain with a frequently non-identified source
Chronic pain
what meidates Normal pain
A-delta and C-fibers
what mediates Pathological pain (hyperalgesia
Pheripheral and central sensitization
where is oral and facial pain processing done
Caudalis (part of the spinal trigeminal nucleus)
what is the sensory portion of the spinal cord
Medullary dorsal horn
pain vs non-pain senations of the medullary Dorsal Horn
Pain is more on the outer surface (supperficial)
non-pain is found deeper
But there is some overlap
what do Nociceptive specific neurons respond to
to only painful stimuli
what do Wide Dyanmic range neurons respond to
Both painful and non-painful stimuli
Does the PNS have something like wide dynamic range neurons
NO
Cell types found in the medullary dorsal horn
Nociceptive specific neurons
Wide Dynamic range neurons
REceptive fields of the Wide Dynamic Range Neurons in the medullary dorsal horn
HAve large Receptive fields
how is the receptive fields of wide Dynamic range neurons different from that of the PNS
PNS can’t be in 2 different branches
where do Nociceptive specific neurons tuerminate in the medullary dorsal horns
In superficial layers I and II
where do Non-nocicpetive neurons terminate in the medullary dorsal horn
In deeper layers III, IV, and V
where does OVerlap occure in the medullary dorsal horn
In layers II and V
Convergence in the medullary dorsal horn
High degree of convergence
what Afferents converge in the MDH
Nocicpetive and Non-nociceptive afferents
what types of things converge in the MDH
Submodality convergence
what emerges in the MDH
wide dynamic range neurons emerge
what happerents to peripheral affernets of different receptive fields
they converge
what peripheral affernts converge their receptive fields
Cutaneous Joint Muscle Tooth pulp (max and Mandibular) other nerves (SLN: superior laryngeal nerve)
Roll of MDH and referred pain
MDH is the neural substrate for referred pain
spread of pain from the teeth
Spread all along the head due to refered pain
how does MDH help to explain referred pain
Pain and non-pain afferents converge on “pain-signaling” neurons
why can’t convergence on the MDH explain Referred pain alone
Because pain only occures under pathological conditions ( not a normal sensation)
what may cause the MDH to start doing referred pain under pathological conditions
something is preventing the activation of convergent input in MDH under “normal” conditions
Does Peripheral sensitization explain referred pain
Not entirely: peripheral sensitization mostly increases with C-fiber sensitivity
- does not explain larger areas of Pain (increased receptive fields)
How could peripheral sensitization explain the larger areas of pain due to referred pain
following severe nerve injury there could be ephaptic connections between pain and non-pain fibers that could enlarge receptive fields
what fibers are used to Induce central sensitization
A-beta fibers
evidence for central sensitization
- Injected Capsacian to Activate TRPV1 giving a burning sensation
- pressure block done near capsaicin, so can’t feel light touch, so no allodynia
- on hand with no pressure block, could feel light touch so there was allodynia
- light touch neuron must communicate with pain nueron to give allodynia when pain is already pressent
what does the pressure block block in the central sensitization test
blocks A-beta and A delta fibers
Steps of Central Sensitization
- C fiber afferent barrage (acute pain, inflammation)
- MDH Neuron response
- Depolarization by substance P (tachykinin)
- modification of NMDA receptor (removal of Mg++ block)
- Increase in conductance NMDA receptor - previously ineffective A-fiber now effective
- A-diber release of glutamate effective at NMDA receptor
- larger receptive field
- response to innocuous stimuli by A-beta fibers now induces pain
Pain threshold of normal teeth
Very high pain threshold
Pain threshold in inflamed teeth
much lower pain threshold
what teeth tend to have lower pain thresholds in the mouth when the tooth is inflammed
Lower pain threshold also in healthy contralateral heathy teeth
why do teeth contralateral to inflammaed teeth expereince low pain thresholds
Inflamed teeth are sensitizing central neurons with input from healthy contralateral side to make them more sensitive
is pain confined to the MDH
Not confined
Effects of trigeminal tractotomy (Cut C1-C3)
Anesthesia (no sensation: C1-C3)
Analgeais (no pain on face)
Hypalgesia (diminished mucosal pain)
Pulpal pain still intact
why do a trigeminal tractotomy
Intractable facial pain from cancer
what is done in a trigeminal tractomy
Descending Vth tract tract cut at level of obex (C1-C3 cut at all afferents)
what happens to stroke patients with lesion in pons
Intraoral touch, thermal, and pain all diminished
what proves that pain is not confined to MDH
TRigeminal tractomy in humans ( intraoral mucosa still shows pain sensations and tooth pulp pain intact)
Lesion in pons (diminishes intraoral and perioral pain)
Afferent pain fibers projecting from the MDH go to the:
Oral Motor N (Pons and Mdeulla
N. submedius
VPM
what is the sensory pain pathway
Afferent fibers
MDH
VPM (thalamus)
S1 (Cortex)
what is the emotional pain pathway
Afferent fibers
MDH
N. Submedius
Cingulate cortex
Roll of the oral motor N in the pain pathways
reflex function:
Jaw opening
sweating
Increased HR and BP
receptive field in the VPM
small
response time of the VMP
Onset/offset of stimulus
what si the response to stimulus of the VPM
linear
receptive field of the submedius
LArge
response time of the N. submedius
outlasts stimulus
what does the N. submedius neurally respresent
NEgative emotion to outlast stimulus
Peripheral changes of phantom pain
Sprouting (neuroma) Ectopic impulses Ephaptic transmission Sympathetic-afferent coupling Down/upregulation og transmitters Down/upregulation of channels and transduction molecules
Central changes for phantom pain
Sprouting Central sensitization (unmasking of synpases
receptive field and why of VPL and Somatosensory cortex in pain processing in the forebrain
Small receptive field nad localization of pain
neural response time of VPL and Somatosensory cortex in pain processing in the forebrain
Neural response track pain stimulus onset and offset
how does the VPL and somatosensory cortex mediate phantom pain
Somatosensory reorganization
Neural response of the N. submedius and Cingulate cortex
Outlasts stimulus (poor localization)
what part of pain does the N. submedius and cingulate corteex involve
the emotional component of pain
effect of anxiety on pain perception
Increases pain perception
empathy and pain
Empathy for another in pain activates some cortical areas
placebo and pain
Suppresses pain perception
How did scientist create a low vs High anxiety condition
Low: Visual cues to indicate whether subject would receive a moderate pain
High: visual cue indicated may receive high pain
results of low and high anxiety test
pain to same stimulus was rated higher in high anxiety state
what happens in the brain following induction of anziety
Increased activity in anerior cinguate cortex
what does Empathy do to the brain
Activates the anterior cingulate and insula
how did they test for empathy
couples get cue for pain
only one person gets pain
both showed pain activity in cinguate cortex
Does empathy also activate SI or SII
Does not activate SI or SII
what does the lack of SI or SII activation for empathy show
separates anatomical difference between emotional and somatosensory component of pain
what does the placebo effect activate
The anterior cingulate cortex like that of opioids
what mediates the placebo effect
endogenous opoids
Roll of Nalxone with testing the placebo
bloacks endogenous opioids so the placebo effect does not work
what do the multiple CNS sites for modulation of pain contain
Endogenous opioids to suppress pain
what are the Multiple CNS sites to modulate pain
Forebrain: ACC
Midbrain: PAG
Rostral ventraomedial medulla
what are the Descending projections from medulla
excitatory
inhibitory
steps of Presynaptic inhibition
Descending projection to local enkephalinergic interneurons
Enkephalins work both pre- and postsynapticall
pre-synaptic suppression of Ca++ channels suppresses neurotransmitter release
Postsynaptic effect of opening K+ channels