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1

Specificity theory of pain

o Pain intensity: degree of injury without consideration of other influences.
o Specificity theory is generally accurate when applied to certain types of injuries and acute pain associated with them. However, does not account for variations in presentations and experiences.
o The above theory assumes once injury is healed the pain is gone, however this is wrong b/c patients are at risk of receiving unnecessary and ineffective dx procedures, drugs, and Tx in search patient’s source of chronic pain.

2

Phantom limb pain

o Sensations may include feeling the limb is still there, or it might be a sensation of chronic pain. Since there’s no ongoing tissue injury in the amputated limb, there should be no chronic pain, the specificity theory can’t account for these findings.

3

Gate control theory (GCT)

o Injury, pain messages originates in nerves associated w the damaged tissue, flow along peripheral nerves to the spinal cord and on up to the brain, roughly equivalent to the specificity theory of pain, and differences in what happens before it reaches brain.
o When the gates open, pain messages “get through” more or less easily and pain can be intense, when gates close, pain messages are prevented from reaching the brain and might not be experienced.

4

Peripheral nervous system

o Sensory nerves bring information about sensory phenomena to the spinal cord from various parts of the body.
o At least 2 types of nerve fibers thought to carry majority of pain messages to spinal cord: A –delta nerve fibers, travel 40 mph (electrical messages, “first or fast” pain) & C-fibers, carry electronical messages at 3 mph “slow or continuous” pain). You hit your elbow and it hurts, so you rub it, then the fibers sends information about pressure and touch to the spinal cord n brain and overrides of the pain messages carried by A-delta and C-fibers.
o Activation of these other types of nerves help explain massages, heat/cold packs, transcutaneous nerve stimulation, acupuncture.

5

Spinal cord and pain

- Pain messages travel along PNS until they reach the spinal cord
- GCT proposes there are "Gates" on the bundle of nerve fibers in spinal cords between the peripheral nerves and the brain
- These spinal nerve gates control the flow of pain messages from the peripheral nerves to the brain

6

Spinal nerve gates:

Factors that affect the spinal nerve gates are the intensity of pain message, competitions from other incoming nerve messages (such as touch, vibration, heat), signals from brain telling the spinal cord to increase or decrease the priority of pain signal

7

The brain and pain:

o Once pain reaches brain it can inhibit or muffle incoming pain signals by producing endorphins (morphine like substances that occur naturally in the human body).

8

What affects the gate?

o Stress, excitement, vigorous exercise, the impact of endorphins is why athletes might not notice pain until games over. That’s why low impact aerobic exercise can be excellent method to help control chronic back pain.

9

A fast pain message...

(A-delta fibers) relayed by spinal cord to specific location in brain (i.e., thalamus and Cerebral cortex). Cortex is where “higher” thinking takes place. Fast pain reaches that and prompts immediate action to reduce pain.

10

A slow pain message...

(C-fibers) takes pathway to the hypothalamus and limbic system. They release certain stress hormones in the body, while limbic system is processing emotions. This is one reason why chronic back pain is often associated with stress, depression, a nd anxiety.

11

Opening/closing pain gates for chronic pain:

- The brain can send and receive signals, relayed between the spinal cord
-Anxiety/ stress may increase pain; the brain can close nerve gates

12

Events and conditions that might open/ cause more suffering:

 Sensory factor, like injury, inactivity, long term narcotic use, poor body mechanics
 Cognitive factor: focusing on chronic pain, apathy, worrying about pain, negative thoughts
 Emotional factors; depression, anger, anxiety, stress, hopelessness.
 Alternatively it can reduce pain, by doing the exact opposite from above.

13

GCT can't explain several chronic pain problems that require...

greater understanding of brain mechanisms

14

Neuromatrix theory

perception of painful stimuli does not result from the brain’s passive registration of tissue trauma, but from its active generation of subjective experiences through network of neurons knowns as neuromatrix

15

o Analysis of phantom limb phenomena (MEZLACK ON EXLAC ) has led to four conclusions:

 Bc phantom limb feels so real, it’s reasonable to conclude the body we normally feel is subserved by the same neural processes in the brain.
 All the qualities we normally feel from body, including, are also felt in the absence of inputs from body.
 The body is perceived as a unity and identified as the “self” distinct from other people and surrounding world
 The brain processes that underlie the body-self are to an extent which can no longer be ignored, “built in” by genetic specification, although is built in substance must of course, be modified by experience.

16

o OVERALL OUTLINE OF NEUROMATRIX THEORY:

 No anatomical substrate of the body self, its widely spread network of neurons that consists of loops between the thalamus and the cortex as well as between the cortex and the limbic system. He (mexlack) labeled this as neuromatrix.

17

o Psychological reasons for a neuromatrix: How do all the little bits of experience and sensory perception come together in a coherent whole? Specificity theory one more time!

 Qualities of a person’s experience is assumed to be inherent in the peripheral nerve fibers, more injury then produces more pain.

18

o NEW CONCEPT of PHANTOM LIMB PAIN:

The new theory of brain function, proposed on the basis of phantom-limb phenomena, provides an explanation for phantom limb pain. Amputees suffer burning, cramping and other qualities of pain.

An excellent series of studies (Krebs et al.,1984; Jensen et al.,1985) found that 72% of amputees had phantom limb pain a week after amputation, and that 60% still continued to suffer phantom limb pain in the long term. The pain is remarkably intractable; although more than 40 forms of treatment have been tried, none has proved to be particularly efficacious (Sherman et al., 1980).

19

Why so much pain in phantom limbs?

- In the absence of modulating inputs from the libs, or body, the neuromatrix produces a signature pattern that is transduced in the sentient neural hub into a hot or burning quality
- The cramping pain, however, may be due to messages to move muscles in order to produce movement
-In the absence of the limbs the messages to move the muscles become more frequent and "stronger" in the attempt to move the limb
-The end result of the output message may be felt as cramping muscle pain
-Shooting pains may have similar origin

20

Neuroplasticity

- NS is adaptable/changeable
-Reorganization is maladaptive when it comes to pain
-Pain signals are more easily triggered and perception of painful input is exaggerated
-One explanation for ongoing experience of pain after injury has resolved
-In tx, seek to use "old" roads that are unhelpful less, and build "new" roads in the brain to promote positive changes