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Understanding Pain Physiology: Nociceptors, Pathways and Modulation
1. Understanding Pain Physiology
Mehmood ul Hassan
Clínical Nurse Instructor
Surgical ICU The Aga Khan University Hospital Karachi Pakistán
10/11/2019
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2. Objectives
By the end of this presentation learner will be able to
1.Describe pain and its component
2.Identify the Nociceptors and its types
3.Distinguish between A-δ Fibers and C Fibers
4.Explain how noxious stimuli converted to nerve impulses
5.Understand the conduction and transmission of pain
impulses
6.Explain the Gate theory and endogenous analgesic system
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4. Pain
• An unpleasant sensory and emotional
experience associated with actual or potential
tissue damage, or described in terms of such
damage
( International Association for the Study of Pain, 2010)
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5. Pain Components
• Sensory
– Feeling of a person regarding pain like sharp, dull,
twisting, throbbing
• Affective
– Emotional reaction like anxious, depressed
• Autonomic
– Activation of sympathetic nervous system increase
heart rate
• Motor
– Movement of body parts10/11/2019
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6. Types of pain
• Nociceptive pain
– It occur due to tissue damage
• Neuropathic pain
– pain caused by damage to, or dysfunction of, the
nervous system
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7. Description of pain
• Acute pain
– that lasts for less than three months and subsides with
healing
• Persistent or chronic pain
– that lasts more than three month
• Cancer pain
– associated with a malignancy
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12. Transduction
Conversion of a stimulus into a nerve impulses
Or
Energy of mechanical, thermal and chemical
noxious stimulus is converted into electrical
signals
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13. Noxious stimuli that can cause
Tissue injury
• Exogenous
– Mechanical injury (cutting, crushing or pinching)
– Thermal injury (extreme heat, steam)
– Chemical injury (acid, )
• Endogenous
– Hypoxia, Ischemia, Infection, Dehydration,
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15. Nociceptors
Sensory neuron that responds to noxious stimuli
and send signals to the spinal cord and brain.
Mechanical Nociceptors
Respond to Cutting, Crushing or Pinching
Thermal Nociceptors
Respond to extreme temperature especially heat
Polymodal Nociceptors
Respond to all kind of damaging stimuli10/11/2019 15
17. Nociceptors location
• They are found in any area of the body that can
sense noxious stimuli either externally or
internally such as skin, tissue, muscle, joint,
bladder, gut and continuing along the digestive
tract.
• They are less present in deep organ
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22. Characteristics of Pain Nerve Fiber
Fast Pain Slow Pain
Occur on the stimulation of
mechanical, chemical and
thermal nociceptors
Carried by small, myelinated
A-delta fibers
Producing sharp, prickling
sensation
Easily localized
Occur first
Occur on stimulation of
polymodal nociceptors
Carried by small, unmyelinated
C fibers
Produce dull, aching, burning
sensation
Poorly localized
Occur second: persistent for long
time: more unpleasant10/11/2019
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26. Transmission
• Release of chemical from terminal ends of first
order neuron and movement of nerve impulses
from second order neuron to somatosensory
cortex
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31. A web page here you can see the
Trigeminothalamic and Spinothalamic
Pathway.
http://axoncomplete.appspot.com/index.html
Trigeminothalamic Pathway
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33. Perception
• Sensation is the conscious or subconscious
awareness of changes in the external or
internal environment. Perception is the
conscious awareness and interpretation of
sensations and is primarily a function of the
cerebral cortex.
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35. Modulation
Human body have endogenous analgesic
system who prevent the body from pain
Endogenous opioid system
Segmental inhibition (Pain gate control theory)
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36. Endogenous Opioid System
• Inhibitory neuron release endogenous opioid
like endorphin, enkepalins, and dynorphin
• These opioid attached with receptor located in
spinal cord, ventral medulla, periaqueductal
gray matter and provide relief from pain
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37. Gate Control Theory
• Melzak and Wall (1965)
• It work as Ascending Inhibition Mechanism, in
which noxious ascending pain impulses
blocked at spinal cord level.
• For example during pain we rub hand its
generate impulses that initiate the inhibition of
pain impulses.
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43. References
• Brunner, L., Suddarth, D., & Smeltzer, S. (2008). Brunner &
Suddarth's textbook of medical-surgical nursing. Philadelphia:
Lippincott Williams & Wilkins
• Falk, S., Bannister, K., & Dickenson, A. (2014). Cancer pain
physiology. British Journal Of Pain, 8(4), 154-162.
doi:10.1177/2049463714545136.
• Basbaum, A., & Bushnell, M. (2009). Science of pain. Oxford:
Elsevier/Academic Press.
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