The Perception of Pain Lecture 27

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The Perception of Pain 11/1/07 Reasons For
Pain Peripheral Sensation of Pain Types of
Pain Neurotransmitters Hyperalgesia Nociception
and Antinociception Mechanisms of
Analgesia Neuropathic Pain
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Pain Is Good!
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Perception of Pain
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Types of Pain

• Nociceptive vs. Neuropathic pain
• Nociceptors
• Thermal
• Mechanical
• Polymodal
• Note nonnoxious stimuli myelinated Aß fibers

nonmyelinated C fibers
5
Kandel figure 24.1
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Abnormal Pain States Hyperalgesia, Allodynia,
Neurogenic inflammation
Kandel figure 24.6
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Peripheral Sensitization Hyperalgesia,
Allodynia, Neurogenic inflammation
Kandel pdf figure 24.7
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Silent Nociceptors
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Spinal Cord Synapses
Noxious
Non-noxious
Nociceptive-Specific Neurons Wide-dynamic-range
Neurons
Kandel pdf Figure 24-2
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Gate Control Theory of Pain
Kandel pdf figure 24.10
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Neurotransmittersin the Dorsal Horn of the
Spinal Cord

• Glutamate
• Neuropeptides
• eg. Substance P
• Notes
• Diffusion distance of neuropeptides
• Central Sensitization

Kandel figure 24.4
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Figure 24-5
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Referred Pain
Kandel pdf figure 24.3
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Centrally Mediated Hyperalgesia

• Windup
• Central Sensitization

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Gate Control Theory of Pain Thunbergs illusion
Kandel Box 24.1
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Gate Control Theory of Pain Thunbergs illusion
Kandel figure 24.9
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5 Pain Pathways
Spinothalamic

• Spinothalamic
• Spinoreticular
• Spinomesencephalic
• Emotional response
• Spinohypothalamic
• Endocrine and cardiovascular responses
• cervicothalamic

Central Pain
Kandel figure 24.8
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Insular Cortex Asymbolia for pain.
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In-Class Exercise

• Where would you target drugs to alleviate pain?
• (which processes or anatomical targets)
• 2. What is the placebo effect and how would you
  test to see if it exists.
• Assuming that it does exist, what do you think
  the mechanism is?

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Potential Targets for Reducing Pain Sensation
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Stimulate Ab fibers
Anterolateral cordotomy
http//apu.sfn.org/content/Publications/BrainFacts
/
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Other Forms of Central Pain

• Thalamic Syndrome
• Phantom Limb Pain
• Other syndrome and symptoms including
  hyperalgesia, allodynia,etc.

Kandel 24.8
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Endogenous Opioids
µ, d, and ? opioid receptors
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Stimulation-Produced Analgesia
Kandel 24.11
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Integration of Descending and Ascending Pathways
in the Spinal Cord
Note Descending serotonin projections can come
from the nucleus raphe magnus descending
norepinephrine pathways can come from the locus
ceruleus
Kandel figure 24-13
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Kandel figure 24-13
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Opioid action 1) Postsynaptic Inhibition -
Increased K conductance 2) Presynaptic
Inhibition - Reduced transmitter release
due to reduced Ca2 influx (direct or
indirect)
Kandel figure 24-13
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Opioids continued

• Stress-induced analgesia
• Nonspecific effects of opioid drugs
• Tolerance
• Addiction
• Chronic opioid-resistant neuropathic pain

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Alternative pain therapies?