Pain theories, history of pain theories, different theories for pain control

1. 1220106

2. CONTENTS
 Introduction to Pain
 Pain Control Theories
 Integration and Application of Pain Theories

3. I cant stand this!
It is derived from the Latin word “poena” meaning
fine, penalty, or punishment.
“An unpleasant sensory & emotional experience
associated with actual or potential tissue damage, or
described in terms of such damage” –
The International Association for the Study of Pain
PAIN

4. What is pain
• Shooting
• Throbbing
• Numb
• Sore
• Burning
• Agony
• Sharp
• Pounding
• Cramping
• Stabbing
• Tender
• Aching
• Annoying
• Debilitating

5. Pathways for pain signals

6. Nociceptors
• Sensitive to repeated or prolonged stimulation
• Mechanosensitive – excited by stress & tissue damage
• Chemosensitive – excited by the release of chemical
mediators
– Bradykinin, Histamine, Prostaglandins, Arachadonic Acid
• Primary Hyperalgesia – due to injury
• Secondary Hyperalgesia – due to spreading of chemical
mediators

7. 1. Specificity Theory
2. Pattern Theory
3. Gate Control Theory
4. Neuromatrix Theory
5. Central Biasing Theory
6. Endogenous Opiates Theory
Pain Control Theories

8. 4 types of sensory receptors – heat,
cold, touch, pain
A nerve responded to only one type
Nerve was continuous from the
periphery to the brain

9. The Pattern theory was incorporated into the
specificity theory which states that there are no specialized
receptors in the skin.
The Specificity theory and Pattern theory are not
sufficient in explaining the experience of pain as the theorists
fail to include any psychological aspects of pain.
Rather, a single “generic” nerve responds differently to each
type of sensation by creating a uniquely coded impulse
formed by a spatiotemporal pattern involving the frequency
and pattern of nerve transmission.
(i.e. Different telephone rings)

11. • With this theory, pain depends on the relative amount of
traffic in two different sensory pathways which carry
information from the sense organs to the brain.
– Slow/Small fibers
• No myelin sheaths, so messages delivered more slowly. Very intense
stimuli (like that caused by a tissue injury) send strong signals on
these slow fibers.
• Slow/small fibers open the gate = you feel pain
– Fast/Large fibers
• Deliver most sensory information to the brain. Covered by fatty
myelin sheaths so delivery is faster.
• Fast/large fibers close the gate = block pain signals
• Explains why:
– Drugs (pain relievers like aspirin)
– Competing stimuli (like acupuncture)
– The mere expectation of treatment effects (like placebos)
can sometimes block pain.
3. Gate Control Theory

13. • Example:
– Bumping the head
• The initial trauma activates the A-
delta and, eventually, C fibers
• Rubbing the traumatized area
stimulates the A-beta fibers, which
activate the SG to close the spinal
gate
• Thus inhibiting transmission of the
painful stimulus

14. Factors which can open the gate
• Physical conditions
Extent of injury
Nature of injury
• Emotional states
Anxiety
Worry
Tension
Depression
• Cognitive states
Focusing on the pain
Boredom
• Lack of activity
Fitness, Exercise

15. • Physical conditions
Medication
Counterstimulation (e.g. heat, massage, accupuncture)
• Emotional state
Positive emotions (e.g., happiness, optimism)
Relaxation
Rest
• Mental state
Intense concentration or distraction
Involvement and interest in activities
• Activity
Fitness, Exercise
Factors which can close the gate

16. Beecher (1946 & 1956) looked at requests for pain relief
amongst soldiers and compared these to the request made
by civilians with the same injuries.
 Most of the soldiers claimed not to perceive any pain and
only a quarter of them requested pain relief.
 80% of civilians asked for analgesic support. Beecher
argued that the context in which the pain was experienced
had an impact on the way in which it was perceived.
Past Experience of Pain
This Gate theory has been widely accepted, but it
leaves unanswered questions, such as chronic pain issues,
sex-based differences and the effects of previous pain
experiences.

17.  In 1999, Melzack and Wall came up with a newer theory
of pain that answered some of these questions. This new
theory, the neuromatrix theory, stipulates that every human
being has an innate network of neurons that they named the
“body-self neuromatrix.”
 Each person’s matrix of neurons is unique and is affected
by all facets of the person’s physical, psychological, and
cognitive traits, and also by their experience.

18. Buxton, 1999
This theory can explain the concept of a “learned behaviour”
This theory builds on the gate theory (acting within the
spinal cord) and addresses brain influences on incoming and
outgoing messages. Cognitive effects can alter sensory
discrimination, the location of the pain source, the intensity of
the pain, or the nature of the pain (eg. Referred pain)
An internal drive or external stimulation can have a strong
influence on thought processes and, therefore, the affect or
perception of pain.

19. Placebo Effect
• Placebo stems from the Latin word for “I shall please”
– Used to describe pain reduction obtained from a
mechanism other than those related to the
physiological effects of the tx.
– Linked to psychological mechanisms
• All Treatments ™ have some degree of placebo effect
– Most studies involving the use of a sham TM
(ultrasound set at the intensity of 0) and an actual
treatment have shown ↓ levels of pain in each group.

20. Castel (1970s)
• Least understood of all the theories
– Stimulation of A-delta & C fibers causes release of B-
endorphins from the Periaquaductal Gray Area (PGA) &
Nucleus Raphe Magnus (NRM) – release serotonin
Or
• ACTH/B-lipotropin is released from the anterior pituitary in
response to pain – broken down into B-endorphins and
corticosteroids
• Mechanism of action – similar to enkephalins to block
ascending nerve impulses
• Examples:
Transcutaneous electrical nerve stimulation TENS
(low freq. & long pulse duration)

22. Using trigger points as an example, pain theories can be
integrated and applied to pain management strategies.
Pain management begins with identifying the source of pain,
decreasing the chemical and mechanical causes, and
facilitating tissue healing.
Therapeutic modalities, medications, exercise, and surgery
are examples of tools used to facilitate tissue healing and
reduce pain. Manual therapies such as muscle energy,
massage, and myofascial release are non-traditional ways
to manage pain