Knowledge of pain physiology is very important in understanding of electrotherapy prescription. So, this slide may be useful in understanding the background of the pain processes.

1. Pain Mechanism
Saurab Sharma, MPT
KUSMS
BPT Year II ; Semester IV
Electrotherapy
Lecture 2

2. Objectives of the session
At the end of the session, you should be able
to:
• Explain the physiology of pain
• Explain the pain pathways
• Explain pain control mechanism
• Understand various dimensions of pain
• Understand aspects of chronic pain

3. Content
• Introduction
• Definition of pain
• Types of pain and their Properties
• Pain Pathways
• Peripheral and Central Aspects
• Modulation of pain
• Referred pain
• Dimensions of pain
• Chronic pain

4. • Understanding of pain mechanism and
pain physiology is necessary for
understanding the usage of
electrotherapy modalities

5. Quiz
• Pain Receptor?
• Types of Nerve fibres?
• Tracts carrying pain sensation?
• Types of pain
• Other tracts?
• Chemical mediators of pain?
• Pain suppressing agents?

6. Types of nerve fibres
Guyton’s Physiology Text Book

7. Pain:
Introduction
•Pain is constructed in the brain
• Pain is a symptom of a disease that needs
investigation to find out etiology
•Pain= friend (in acute)
•Occurs in case of tissue damage
•What if pain is lost?

8. Pain:
Introduction
• Is it always a friend?
• Does it always occur after tissue damage?
• Does every pain indicate local tissue
damage?

9. Types of pain (Guyton)
Fast pain Slow pain
Perceived in 0.1 seconds
after application of stimuli
perceived after 1 sec and
last for few seconds to
minutes
known as sharp pain, acute
pain
known as aching pain,
chronic pain, slow burning
pain, throbbing pain,
nauseous pain
not felt in the deeper
tissues
can be felt in both superficial
and deeper tissue and organ
eg: needle prick, cut, burn, leads to prolonged suffering

10. How is the pain is perceived?
• PERPHERAL MECHANISM
–Nociceptors
–Peripheral Nerves
• CENTRAL MECHANISM
–Spinal cord
–Brain stem
– Cerebral cortex

11. Nociceptors
• The receptors responding preferentially to
noxious stimulus
• Free nerve endings- skin, periosteum, joint
capsule etc
• Deeper organs are sparsely supplied by pain
receptors
• Pain is elicited by mechanical, thermal and
chemical stimuli.

12. Nociceptors
• Chemical substances- bradykinin, histamine, serotonin,
acids, acetylcholine and proteolytic enzymes
• Mechanical nocioceptors are such that they are
activated by extreme pressure.
• Prostaglandins and substance P enhances the
sensitivity of nerve endings and contribute in chronic pain
• Polymodal receptors: are the thermal receptors
(respond to temperature more than 40 degrees and
extreme cold) that respond to variety of stimuli in graded
manner.

13. Peripheral nerve
C= chemical/ slow pain

14. Central Mechanism of Pain:
Spinal Cord
I- Lamina
marginalis:
fast pain
II and III-
SGR: slow
pain; C
fibres

15. Spinal relay neurons in dorsal horn
1. Specific nociceptive neurons: A delta, C
fibres
2. Nonspecific nociceptive neurons: Wide
dynamic Range (WDR) neurons- mainly in
layer V
3. Non-nociceptive specific neurons

16. Central Mechanism of Pain:
Spinal Cord: Referred Pain
Guyton’s Physiology Text Book

17. Central Mechanism of Pain:
Spinal Cord: Wind up
• Specific neuronal plasticity
• Receptive field expands sensitizing nervous
system
• Due to WDR neuron

18. GATE CONTROL THEORY
• Ronald Melzack and Patrick Wall (1965)
• Gating system in CNS opens and closes to
allow the pain signals to the brain or to block the
signals
• Larger nerves inhibit the transmission of pain
signals by smaller nerves through the gate

19. GATE CONTROL THEORY
• The dorsal column fibers send collaterals to
the cells of substantia gelatinosa

20. GATE CONTROL THEORY
• Touch sensation inhibits the release of
substance P by the pain fibers ending in
substantia gelatinosa, so the pain sensation is
suppressed.
• Thus gating of pain in posterior gray horn is
similar to presynaptic inhibition.
• This forms the basis for relief of pain through
rubbing, massage techniques and application of
ice packs.

21. Pain Suppression (Analgesia) System
in
the Brain and Spinal Cord

22. Pain Suppression:
Analgesia System
• Different reactions to pain in different individual
• Reason: Analgesia system
• Definition: Capability of the brain itself to
suppress input of pain signals to the nervous
system by activating a pain control system

23. Pain Suppression:
Analgesia System
Three major components
1. The periaqueductal gray and periventricular
areas of the midbrain & upper pons
2. The raphe magnus nucleus, a thin midline
nucleus located in the lower pons and the upper
medulla
3. Pain inhibitory complex located in the dorsal
horns of the spinal cord.

24. Pain Suppression:
Analgesia System
• Several transmitters are involved in the
analgesia system: enkephalin and endorphin
• Many fibers derived from the periventricular
nuclei and from the periaqueductal gray area
secrete enkephalin at their endings.
• Fibers originating in this area send signals to
dorsal horns of the spinal cord to secrete
serotonin at their endings.

25. Pain Suppression:
Analgesia System
• The serotonin causes local cord neurons to
secrete enkephalin as well.
• The enkephalin is suppose to cause both
presynaptic and post synaptic inhibition of
incoming type C and type A delta fibers where
they synapse in dorsal horns.

26. Nociception
Low threshold mechanoreceptor
Low threshold mechanoreceptor
Nociception Pain
Touch

27. Low threshold mechanoreceptor
Low threshold mechanoreceptor
Touch
Touch

28. Treatment of Pain by
Electrical Stimulation:
1. Peripheral stimulation by stimulating the dorsal
sensory columns.
2. Stereotaxic stimulation of brain parts: appropriate
intralaminar nuclei of the thalamus or in the
periventricular or periaqueductal area of the
diencephalon.
• Dramatic relief has been reported, where pain relief
has lasted for as long as 24 hours after only a few
minutes of stimulation.

29. Pain control mechanisms
1. Spinal segmental influences
2. Descending inhibitory influences from the brainstem
3. Facilitating descending influences
4. Diffuse noxious inhibitory controls

30. Sensory findings in
Non-nociceptive pain
• Tissue pathology – poor correlation
• Quantitative –hyperalgesia
• Qualitative – allodynia, paresthesia,
Dysaesthesias
• Spatial – radiation
• Temporal – increased latency, after discharge,

31. Features of Chronic Pain
• No identifiable tissue damage appropriate to
nature and intensity of pain
• No correlation between investigative findings
and symptoms
• Disability is chronic and secondary effects of
inactivity eventuate
• A passive attitude to management

32. Features of Chronic Pain
• Diffuse and non specific area of pain
• Centrally evoked pain
• Constant pain
• No specific aggravating factors
• No stimulus - response predictability
• Fear, anger and anxiety
• Fear avoidance behavior
• Pain catastrophization

33. “Models” of Chronic Pain?
• Osteoarthritis
• Lower back pain
• Diabetic neuropathy
• Cancer pain
• Fibromyalgia and Chronic fatigue
syndrome
• Neck pain
• Neuropathic pain

34. Dimensions of pain
• Sensory-discriminatory
• Affective and emotional: anxiety, depression
• Cognitive: attention, anticipation, culture,
religion, social group, previous pain memory
• Behavioral: verbal/ non verbal- posture, facial
expression, moaning, treatment seeking

35. Bio-psycho-social model of pain

36. Bio-psycho-social model of pain

37. Bio-psycho-social model of pain

39. Cognitive- negative

40. Cognitive- Positive

41. Treatment
• Biopsychosocial approach of treatment

42. Summary
• I try too hard to be ordinary. Only at
times I succeed