Central Pain Flashcards
Trigeminal pain fibers terminate in which structure?
Medullary dorsal horn (nucleus caudalis)
T/F: CN V pain fibers terminate in the superficial parts of the nucleus caudalis.
TRUE
T/F: Only pain fibers come in to the nucleus caudalis.
FALSE
T/F: WIde dynamic range neurons and nociceptive specific neurons are similar to the peripheral neurons.
FALSE
Wide dynamic range neurons are different
Both are found in the nucleus caudalis
What makes wide dynamic range neurons different?
Can respond to pain, heat, and light touch
T/F: Central neurons seem to have larger receptive fields than peripheral neurons.
TRUE
How does the convergence of multiple fiber types in the MDH explain referred pain?
Both pain and non pain peripheral nerves converge on “pain sensing” central neurons
What receptor is activated by capsaicin?
TRPV1
Patients with a capsaicin injection report allodynia (pain to light touch) around the injection. Blocking the A-beta and A-delta nerves stops the allodynia. What does this say about the mechanism?
A-beta and a-delta fibers must be active for allodynia to occur
Describe central sensitization’s role in allodynia.
Light touch mechanoreceptor have synapse with central nociceptor specific neuron but is normally inactive. Central sensitization causes this synapse to become active and light touch will stimulate central pain
Describe the mechanism for activating a central neuron.
C-fiber releases glutamate and substance P -> opens NMDA receptor -> Ca rushes into central neuron
When activating a central nerve, what are the roles of glutamate and substance P in opening the NMDA channel?
Glutamate: binds to receptor to open channel
Substance P: removes magnesium block from channel
Although A-beta fibers have synapse on central pain nerve, why is it inactive?
A-beta releases glutamate but not Substance P so NMDA stays blocked
Why does allodynia require pain fibers AND mechanoreceptors to be active?
C-fiber releases substance P to unblock NMDA channels for A-beta’s glutamate to engage
How can an inflamed tooth on one side of the mouth cause the contralateral healthy tooth to be more sensitive?
Central sensitization: A-beta fiber activation at the nucleus
T/F: The medullary dorsal horn is the only structure that mediates central pain.
FALSE
What structures of the mouth still signal pain even with a cut CN V at the medullary dorsal horn level?
Pulp of tooth
Mucosal pain lessened but not removed
What are the three pathways of efferent fibers from the medullary dorsal horn?
Reflex: remain in brainstem
Sensory: -> VPL -> cortex
Emotional: -> nucleus submedius -> cingulate cortex
What are some differences between central responses to pain in the VPL vs nucleus submedius.
VPL = small receptive field, on/off stimulus, linear response
N. submedius = large receptive field, longer response, outlasts stimulus
What is happening in the central nervous system during phantom pain?
A certain activity from one part of body is causing a response in cortical areas it shouldn’t
T/F: Anxiety can cause someone to be more sensitive to pain.
TRUE
Higher activation in cingulate cortex
T/F: Empathy for another’s pain can activate both the cingulate cortex and the somatosensory cortex.
FALSE
Just cingulate cortex
How can a placebo effect pain?
Can downregulate response in the cingulate cortex
How can descending pathways contribute to pain regulation?
CIngulate cortex can send a signal to the brainstem -> multiple ligands are receptors used to release opioids
Also descending projections synapse with afferent peripherals to suppress substance P
