Pain is a complex experience involving sensory and emotional components. It is initiated by noxious stimuli and transmitted along specialized pain pathways in the nervous system. There are different types of pain including nociceptive, inflammatory, neuropathic, and functional pain. Pain signals are transmitted via fast Aδ fibers and slow C fibers from receptors to the spinal cord and then to the brain. The transmission of pain can be modulated by descending pathways and inhibited using various pharmacological and surgical techniques. Managing pain involves understanding its underlying causes and mechanisms.

1. PHYSIOLOGY OF PAIN AND
PAIN PATHWAYS
Dr. Divvi Anusha
1st year MDS
Department of Public Health Dentistry

2. CONTENTS
• Introduction
• History of pain
• Definition of pain
• Characteristics of pain
• Factors affecting pain
• Components of pain sensation

3. • Receptors of pain
• Theories of pain
• Pain pathways
• Inhibition of pain transmission
• Referred pain
• Conclusion
• References

4. INTRODUCTION
• Pain is an intensely subjective experience, and is
therefore difficult to describe.
• It has two features which are nearly universal.
 It is an unpleasant experience
 It is evoked by a stimulus which is actually
or potentially damaging to living tissues.

5. • Pain has two components:
 awareness of a painful stimulus
 emotional impact (or effect) evoked by the
experience.
• Awareness is localized to the area stimulated, the
experience involves the whole being.
• Even a finger is hurt, the whole person suffers.

6. HISTORY
• Derived from Latin word “POENA”
• Homer – Arrows shot by God
• Aristotle – Passion of the soul
• Plato – within the body
• Bible – anguish of the soul

7. DEFINITION OF PAIN
• Pain is defined as “an unpleasant sensory and
emotional experience associated with actual or
potential tissue damage, or described in terms of
such damage.”
(The International Association for the Study of Pain)

8. • According to Monheim, pain is “ an unpleasant
emotional experience usually initiated by noxious
stimulus and transmitted over a specialized neural
network to the CNS where it is interpreted as
such.”

9. CHARACTERISTICS OF PAIN
1. Threshold and intensity
2. Adaptation
3. Localization of pain
4. Rate of tissue damage

10. CLASSIFICATION OF PAIN
• Based on pathophysiology pain can be classified
in to four categories:
 Nociceptive pain
 Inflammatory pain
 Neuropathic pain
 Functional pain

11. Nociceptive pain
 Transient pain in response to noxious stimulus
 Arises from the stimulus outside of nervous
system
 Protective as it prevents further injury.

12. Inflammatory pain
 Initiated by tissue damage or inflammation
 Arises from a stimulus outside of the nervous
system
 It is mal-adaptive
 Ex. Osteoarthritis, Rheumatoid arthritis

13. Neuropathic pain
 Caused by the dysfunction in the nervous
system
 Ex. Diabetic neuropathy

14. Functional pain
Associated with abnormal neural processing
Ex. Fibromyalgia

16. FACTORS AFFECTING PAIN
1. Emotional status
2. Fatigue
3. Age
4. Racial and nationality characteristics
5. Sex
6. Fear and apprehension

17. COMPONENTS OF PAIN SENSATION
• Pain sensation has two components
 Fast pain
 Slow pain
• Receptors for both the components of pain are
same but the afferent nerve fibers are different.
• Fast pain is carried by Aδ fibers and slow pain is
carried by C type of nerve fibers

19. RECEPTORS OF PAIN
• Free nerve endings (nociceptors)
• Widespread in superficial layers of skin and in
certain internal organs.
• Deep tissues are weakly supplied with nerve
endings.

21. • Three different types of stimuli excite pain
receptors:
 Mechanical
 Thermal
 Chemical
• Fast pain is elicited by the mechanical and thermal
types of receptors
• Slow pain can be elicited by all three types

22. THEORIES OF PAIN
Intensity theory
 Pain is produced when any sensory nerve is
stimulated beyond a certain level
 Trigeminal system provides an example against
this theory

23. Specificity theory
 Pain is a specific modality equivalent to vision and
hearing etc.
 But concept of specific nerve ending s is no long
tenable.

24. Pattern theory
 1894 – Goldscheider
 Stimulus intensity and central summation are the
critical determinants
 Summation of sensory input
 Pain results when the total output of cells exceeds
a critical level.

25. Gate control theory
 1965 - Ronald Melzack and Patrick Wall
 Considered to be one of the most influential
theories of pain
 Asserts that non-painful input closes the "gates" to
painful input, preventing pain sensation from
travelling to CNS

26. • Stimulation by non noxious input is able to
suppress pain
• Two destinations – transmission cells and the
inhibitory interneurons
• The more the large fiber activity at the inhibitory
cell, the less pain is felt.
• This theory offers physiological explanation

27. PAIN
PATHWAYS

28. Dual pathways for pain transmission
• From peripheral receptors to spinal cord:
Aδ fibers (fast fibers) – for fast pain
C fibers (slow fibers) – for slow pain
• From spinal cord to brain: via Anterolateral
(Spinothalamic) tract
Neo-spinothalamic tract – for fast pain
Paleo-spinothalamic tract – for slow pain

29. Thalamus – ventrobasal complex
Reticular formation
Spinothalamic tract
Spinal cord
(lamina I – lamina marginalis)
Peripheral fibers
Aδ fibers
Pain receptor
(Free nerve endings)
Somatosensory cortex
Other basal areas of brain

31. Reticular nuclei,Tectal area &
periaqueduvtal grey region
Thalamus
Spinothalamic tract
Spinal cord
(lamina II & III – substantia gelatinosa)
Peripheral fibers
C fibers
Pain receptor
(Free nerve endings)
Thalamus
Hypothalamus
Other basal areas of brain

32. DESCENDING PAIN PATHWAY
• Descending Pain Modulation
(Descending Pain Control Mechanism)
• Transmit impulses from the brain (corticospinal
tract in the cortex) to the spinal cord (lamina)

33. • Periaquaductal Gray Area (PGA) – release
enkephalins
• Nucleus Raphe Magnus (NRM) – release
serotonin
• Release of these neurotransmitters inhibit
ascending neurons
• Endogenous opioid peptides - endorphins &
enkephalins causes analgesia.

34. REFERRED PAIN
• Definition
The pain sensation produced in some part of the
body felt in other structures away from the place
of development is called referred pain.
• Deep pain and some visceral pain are referred to
other areas but superficial pain is not referred.

35. MECHANISM OF REFERRED PAIN
• Branches of the visceral pain fibers synapse in the
spinal cord with some of the 2nd order neurons that
receives pain fibers from the skin.

37. APPLIED PHYSIOLOGY
• Analgesia
• Paralgesia
• Phantom limb pain
• Hyperalgesia
• Allodynia.

38. CLINICAL ABNORMALITIES OF PAIN
• Thalamic syndrome
• Herpes zoster
• Tic douloureux
• The brown – sequard syndrome
• Atypical facial pain

39. THALAMIC SYNDROME
• Thrombosis of posterior cerebellar artery
• Posterior nuclear group of thalamus becomes
degenerated
• Medial and anterior nuclei remain intact
• Loss of sensations from the opposite side of body
• Ataxia
• After few weeks sensory perception of opposite
side of body returns

40. HERPES ZOSTER
• The cause of pain is presumably by the excitation
of the neuronal cells of the dorsal root ganglion by
the virus infection
• Along with pain, also causes rash

41. THE BROWN – SEQUARD SYNDROME

42. ATYPICAL ODONTALGIA
• Atypical facial pain, phantom tooth pain, or
neuropathic orofacial pain.
• Characterized by chronic pain in a tooth or teeth,
or in a site where teeth have been extracted or
following endodontic treatment.
• Over time, the pain may spread to involve wider
areas of the face or jaws.

43. • The pain is called “atypical” because it is a
different type of pain than that of a typical
toothache.
• Treated by using a variety of medications
• Tricyclic antidepressants are used most frequently.
• Amitriptyline is more commonly prescribed

44. • Microvascular decompression
• Glycerol injection
• Balloon compression
• Stereotactic radiosurgery
• Generally, treatment is successful in reducing the
pain but not eliminating it completely.

45. INHIBITION OF PAIN TRANSMISSION
• Pain sensations may be controlled by interrupting
the pain impulse
• may be done chemically, surgically
• Pain sensations respond to pain reducing
drugs/analgesics
• Occasionally pain may be controlled only by
surgery.

46. • Sympathectomy – excision of portion of neural
tissue from autonomic nervous system.
• Cordotomy – severing of spinal cord tract, usually
the lateral spinothalamic.
• Rhizotomy – cutting of sensory nerve roots.
• Prefrontal lobotomy – destruction of tracts that
connect the thalamus with prefrontal and frontal
lobes of cerebral cortex.

47. Newer Approaches
Transcutaneous Neural Stimulation (TNS)
• Cutaneous bipolar surface electrodes are placed in
the painful body regions
• Low voltage electric currents are passed.
• Intense stimulation is maintained for at least an
hour daily for 3 weeks.

49. • Acupuncture is also used to relieve pain.
• This is based upon the pain inhibitory mechanism
of encephalins and endorphins
• Needles are inserted through selected areas of skin
and then twirled.
• After 20-30 minutes, pain is deadened for 6-8
hours

50. • Location of needle insertion depends on part of
body acupuncturist wishes to anesthetize.
• Example : to pull a tooth – a needle is inserted in
the web between thumb and index finger.

52. CONCLUSION
• Pain is bad, but not feeling pain can be worse
• Individuals with congenital absence of pain
receptors are extremely rare but not unknown
• Such individuals are very poor at avoiding
accidental injuries
• As a result, their life span is usually short

53. • Thus pain, although unpleasant, is a protective
sensation with enormous survival value.
• Managing pain is by understanding the problem
and cause of pain

54. REFERENCES
1. Text book of Medical Physiology, 2nd edition,
Chaudhari.
2. Text book of Medical Physiology, 8th edition,
Arther C Gyton.
3. Textbook of medical physiology,3rd edition,
Chatterjee
4. Pain – Wikipedia, the free encyclopedia

55. THANKYOU