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Putting Pain in a New Perspective, Or…. Mary Christenson, PT, PhD DPT 781 O. What Makes Pain Matter?. Traditional Model Papercut stimulates free nerve endings of mechanical nociceptors Travels via A delta and C fibers to the dorsal horn of the spinal cord

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Putting pain in a new perspective or

Putting Pain in a New Perspective, Or…

Mary Christenson, PT, PhD

DPT 781 O


What makes pain matter
What Makes Pain Matter?

  • Traditional Model

    • Papercut stimulates free nerve endings of mechanical nociceptors

    • Travels via A delta and C fibers to the dorsal horn of the spinal cord

    • Synapse on second neuron in substantia gelatinosa / T cell, crosses midline and joins the anterolateral spinothalamic system

    • Travels to ventral posterior lateral nucleus of thalamus where synapses on third neuron

    • Information carried to area of the primary somatosensory cortex which interprets “papercut - pain”


Personal stories need for a new model
Personal Stories: Need for a New Model?

  • Phantom Limb Pain

  • CRPS

  • Traumatic injuries where a greater threat is perceived

  • Life more important than pain

  • Step on a Tack:

    • Basic

    • Up a notch


Pain versus tissue injury
Pain versus Tissue Injury

  • “Pain does not provide a measure of the state of the tissues.” 1

  • % people with bad OA and no pain?

  • % people with bad disc protrusion and no pain?

  • Etc.


Questions
Questions

  • Have you ever had no pain with damage to your body?

  • Have you ever experienced pain when no damage has occurred to your body?


The threat
The Threat

  • Get pain when brain perceives there is a potential for danger to tissues and action is needed

  • The brain is managing countless messages in very short time intervals – determines priorities”

Brain = “Orchestra” per Butler and Moseley2


Rethinking sensors
Rethinking Sensors

  • Sensors = receptors = “reporters”2 keeping track of the body’s business

  • Located in walls and at the free nerve endings of neurons

  • Stimulation can open receptors, ions exchanged, action potential

  • Rapid turnover of sensors? Importance?

  • Can increase/decrease in number – Result?


Spinal cord involvement
Spinal Cord Involvement

  • Messages can come from the brain to shut down neurotransmission of signals from 2nd order neurons (“danger messengers”1)

  • Powerful chemicals (stories) reverse flow of ions and therefore can stop signals


Rethinking the brain s involvement

Many centers in the brain involved in pain to interpret and respond

Pre-motor/motor cortex

Cingulate cortex

Pre-frontal

Amygdala

Sensory cortex

Hypothalamus/ thalamus

Cerebellum

Hippocampus2

Rethinking the Brain’s Involvement


Peripheral sensitization
Peripheral Sensitization respond

  • Increased responsiveness to stimuli after initial injury

  • Potential mechanisms:

    • Lower threshold to stimulus

    • Increase in neuron activity

    • Increase in area of receptor fields

    • Increase in response to the same stimulus


Central sensitization
Central Sensitization respond

  • Neurons in dorsal horn

    • High-threshold – respond to noxious stim

    • Low-threshold – respond to innocuous stim

    • Wide-dynamic-range (WDR) – respond to both

  • Tissue injury: increased sensitivity of high-threshold and WDR neurons

    • Expansion of receptive fields in central neurons common

  • As pain persists, neurons in brain that induce pain become sensitized


Sensitization
Sensitization respond

  • Continued input from sensitized nociceptors can maintain sensitization of dorsal horn neurons

    • Need to reduce peripheral input?

  • Sensitization of dorsal horn neurons can also be maintained in absence of peripheral input

    • Need to reduce central sensitization?


Multiple sites within the brain decision making power
Multiple Sites within the Brain – Decision-Making Power respond

  • Brain has billions of neurons – each neuron can connect with up to 5000 other neurons


At first glance is the yellow panel in front or back
At first glance: respondIs the yellow panel in front or back?

http://www.bing.com/images/search?q=3+d+box+optical+illusion&go=&form=QBIR&qs=n&sk=#focal=aa51b477d526faca84a9a39bfdf0456a&furl=http%3A%2F%2Fwww.at-bristol.org.uk%2Fassets%2Fimages%2Fillusions%2F11.%2520The%2520Necker%2520Cube.jpg


The neuromatrix model
The Neuromatrix Model respond

  • Pain is Complex

  • The Neuromatrix Theory2

    • Neuromatrix distributed throughout brain

    • Wide network of neurons that generate patterns

    • Processes information flowing through it

    • Produces a pattern felt as whole body

    • Pain is an event that takes up part of this space

    • Event space = neurosignature


The threat danger
The Threat: “Danger” respond

  • Body Perceives a Threat

    • Many systems engage

      • Endocrine/hormones – down and up regulate

      • Motor – Mobilizes

      • ANS

        • SNS – increase HR, metabolism, “awareness”

        • PNS – will act in healing processes

      • Immune – fight “invasion,” heal, sensitize

      • Pain – motivator: get help, prompt to move

    • Pain may be the conscious response to threat


It is the perception of the threat that determines the output, not the tissue damage itself or threat to the tissues…1Neuromatrix TheoryThe Brain Interprets the Messages Received to Determine an Output


The pain experience
The Pain Experience output, not the tissue damage itself or threat to the tissues…

  • Somatic

  • Psychological

    • Attention

    • Anxiety

    • Expectation

    • Meaning of pain

  • Social

    • Provides context to the pain


Patient and clinician education
Patient and Clinician Education output, not the tissue damage itself or threat to the tissues…

  • What effect will each of these (listed on previous slide) influences have on the perceived threat?

  • CRPS


Change in the brain remember the homunculus

Proprioceptive representation of pained part changes in primary somatosensory cortex1

Change in the Brain:Remember the Homunculus?


Homunculus
Homunculus primary somatosensory cortex

  • Skin and soft tissue representation

  • Change in representation of parts of the brain;

    • Example: phantom limb pain4

  • “Use-dependent brain”2

  • Demand more of a part, representation in the brain will be bigger – ex. musicians


How persistent pain develops
How persistent pain develops primary somatosensory cortex

  • Tissue injury may not be present – pain continues

  • Continued input sensitizes central neurons

  • Pain can occur without tissue damage


Brain imaging
Brain Imaging primary somatosensory cortex


Soooo how can we help our patients with persistent pain
SOOOO…How can we help our patients with persistent pain? primary somatosensory cortex

  • It’s time for lab…..


References
References primary somatosensory cortex

  • 1Moseley GL. Reconceptualizing pain according to modern pain science. Phys Ther Reviews. 2007;12:169-178.

  • 2Butler D, Moseley GL. Explain Pain. Adelaide: NOI Group Publishing, 2003.

  • 3Melzack R. Evolution of the neuromatrix theory of pain. The Prithvi Raj Lecture: Presented at the Third World Congress of World Institutes of Pain, Barcelona 2004. Pain Practice. 2005;5(2):85-94

  • 4Colapinto J. Brain games: The Marco Polo of neuroscience. The New Yorker. May 3, 2009.


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