This document provides an overview of the physiology of pain. It begins with a brief history of pain theories, then defines pain and discusses its classification. The document outlines the mechanism of pain perception, including the roles of sensory receptors, neurons, and ascending and descending pain pathways in the spinal cord and brain. It also addresses factors that affect pain perception as well as electrophysiology concepts like action potentials. The document concludes by discussing pain in unborn children and referencing additional resources.

1. GOODMORNING

2. PHYSIOLOGY OF
PAIN

3. “PAIN A PERCEPTION,
NOT
REALLY A
SENSATION”
PRESENTED BY
KHUSHBOO BARJATYA
PG STUDENT
DEPT OF PEDODONTICS

4. CONTENTS
• Introduction.
• History.
• Definition.
• Classification.
• Mechanism of pain perception.
• Pain control theory.
• Factors affecting pain.
• Electrophysiology of pain.
• Pain of unborn
• Conclusion.
• References.

5. ELUSIVE NATURE
OF PAIN

6. PAIN A PROTECTIVE
MECHANISM OF BODY

7. HISTORICALLY
• Arrow shot by god
•Magic, Evils, Demons.
•The Greeks and Romans first
who gave theory of sensation and
idea that brain responsible for
perception of pain.

8. WHAT IS
PAIN ?

9. The Latin word "poena" meaning a fine, a
penalty.
• First given as early as 1968 by Margo
McCaffery:
• “Pain is whatever the experiencing person
says it is, existing whenever he says it
does”
• WHO has defined pain as
“An unpleasant sensory or
emotional experience associated with
actual or potential tissue damage, or
described in terms of such damage”.
The International Association for the Study of Pain
• The American Academy of
Pain Medicine defines pain as –
“An unpleasant sensation and
emotional response to that
sensation

10. CLASSIFICATION OF
PAIN
Acute
pain
Chronic
pain
Neuropathic
pain
Peripheral central
Nociceptive
pain
Somatic
pain
Visceral
pain
Jensen, 1996

11. ALLODYNIA
1. Certain types of noxious stimulus (e.g.
sunburn, injury, post-surgical wounds)
may result in the individual perceiving
pain in response to stimuli that are not
normally painful, such as a light stroking
of the skin
2. Certain noxious stimuli (e.g. severe
bruising) can result in the individual
perceiving abnormally high levels of pain
in response to normal noxious stimuli
such as a small scratch; in such cases,
patients often perceive spontaneous pain
HYPERALGESIA

12. • PARESTHESIA:
• It is abnormal sensation which is described as
“pins and needles”. It can occur either
spontaneously or evoked by certain stimuli.
• DYSESTHESIA:
• An unpleasant abnormal sensation, whether spontaneous
or evoke.
• Note: difference being paresthesia is not
unpleasant while dysthesia is!
• .

13. • HYPERPATHIA:
• It is painful syndrome resulting from abnormally
painful reaction to stimulus. The stimulus is repetitive
with an increased pain threshold.
• PAIN THRESHOLD:
• Amount of pain required before individual feel the
pain. the higher the threshold, the more pain one can
endure.
• PAIN TOLERANCE LEVEL
• The greatest level of pain which a subject can
tolerate.

14. Complex Regional Pain Syndrome I:

15. Complex Regional Pain Syndrome II
Causalgia, Damaged nerve

16. .
PHANTOM LIMB PAIN:

17. MECHANISM OF PAIN

18. NEURONS IN PAIN
PHYSIOLOGY

19. ORGANIZATIONAL ELEMENTS OF
PAIN
1.Transduction/Detection
2.Transmission/Processing
3.Perception
4.Modulation

20. SENSORY RECEPTORS
Free nerve endings,are referred to as nociceptors.
• C-fiber mechano/heat-sensitive nociceptors (CMH)
• A-fiber mechano/heat –sensitive nociceptors (AMH).
• A-delta fibers are thinly myelinated fibers which
conduct in the range of 2 m/s to 20 m/s. are termed high
threshold mechanoreceptors.(first pain)
• C-fibers are non-myelinated fibers that conduct in the
range of 0.5 m/s to 2 m/s and transmit noxious
information from a variety of modalities including
mechanical, thermal, and chemical so, they are termed
C-polymodal nociceptors.(second pain)
DETECTION

21. Classification of nerve fibres
Fibre type Function Axon diameter mm Conduction
/ Myelin + - velocity, m per s
Aα (I) motor a - fibres 9-18/+ 70-120
spindle afferents
(Ia)
tendon organs (Ib)
Aβ(II) touch and
pressure
5-12/+ 30-75
Aγ (II) motor to muscle
spindles
3-6/+ 18-36
Aδ(III) pain, pressure,
temperature
1-5/- 4-30
B (III) Preganglionic ANS 3/- 3-12
C (IV) pain, sympathetic 1/- 1-2

22. INNERVATION OF DENTAL
PULP
immunohistochemistry

23. PROCESSING

25. DESCENDING NEURON

27. Projection
Neuron
Low
Threshold
Wide Dynamic
Range(WDR)
Nociceptive
specific N.

28. REFFERED
PAIN

29. QUESTIONS ?
• Why Anginal pain felt in left arm?
• Is pain from one Tooth transferred
to another?
• Why pain in Neck leads to
Headache?

30. TWO THEORIES
1.Convergence– Projection
2.Convergence-Facilitation

33. INFLAMED DENTAL PULP
• Normally nociceptors remain quiescent, but
activated by modest temperature change or stimuli
leads to pain.
• Process involve complex neuro-immune
interactions.
• Both pheripheral and central projections are
important.

34. Peripheral Nerve Sensitivity
• Tissue damage results in a drop in pH and
release of chemicals, e.g. histamines and
bradykinin, to which small non-myelinated C
fibers are sensitive.
• Substance P may also be released peripherally
with resultant increase in peripheral vasodilation
and further sensitization of the C fibre's
peripheral ending.

35. Altered nerve activity

36. Allodynia in Irreversible Pulpitis

37. PAIN PATHWAYS

38. Spinocerebral
Ascending
Pathways
Spinoreticular
pathway
Spinothalamic
pathway
Spinohypothalamic
pathway
Spino
mesencephalic
tract
Dorsal
column
pathway

39. Spinothalamic pathway

41. Ventral posterolateral Nucleus
Intra-laminar nuclei

42. Tract Lateral-STT Lateral-STT
Spinoreticular tract (SRT)
Origin Lamina I & IV, V Lamina I, IV,V, (and
VII, VIII)
Somatotopic organisation Yes No
Body representation Contralateral Bilateral
Synapse in reticular formation No Yes
Sub-cortical targets None Hypothalamus Limbic
system Autonomic
centres
Thalamic nucleus Ventral posterolateral
(VPL)
Intra-laminar nuclei
Other midline nuclei
Cortical location Parietal lobe (SI cortex) Cingulate gyrus
Role Discriminative pain (quality
intensity, location)
Affective-arousal
components of pain
Other functions Temperature
Simple touch

43. Temporal summation. If a stimulus arrives at the
synapse in the dorsal horn more frequently than once
every 3 seconds, the post-synaptic electrical discharge
becomes more prolonged, with consequent increase in
the severity of the pain. This temporal summation is
termed "windup"

44. IS THERE A
“CORTICAL PAIN”
CENTER?

45. Brodmann's tissue classification

46. Dennis Turk's claim that "the
reign of pain is mainly in the
brain". But there is no one
centre "in control".

47. PAIN THEORIES

48. SPECIFICITY THEORY
• Pain and touch sensors on the skin are wired
to a pain centre in the brain.
• This theory does not account for pain when
there is no organic basis for the pain.
BY DESCARTE
IN 1644

49. SENSORY DECISION THEORY
This theory relies heavily on the psychological
perception of a painful stimulus.
Painful stimuli is perceived according to the
individuals cognitive processesPATTERN THEORIES
By Goldscheider in 1894
Pain conducting nerves are shared with
other sensory nerves- pattern of activity
from the nerve cells dictates how the
pattern is interpreted.

50. GATE CONTROL THEORY
• The idea that the perception of pain is not a
direct result of activation of nociceptors, but
instead is modulated by interaction between
different neurons, both pain-transmitting and
non-pain-transmitting. The theory asserts that
activation of nerves that do not transmit pain
signals can interfere with signals from pain
fibers and inhibit an individual's perception of
pain.
Ronald Melzack (a Canadian psychologist) and Patrick David
Wall (a British physician) in 1962,

51. Inhibition is in blue, excitation in yellow

52. Inhibition is in blue, excitation in yellow

53. FACTORS AFFECTING
PAIN

54. AGE
• Children and elderly are of concern. Children, more sensitive
than adults.
• As-
• Show more inflammatory response to
pain.
•The pain signals reach brain in full
intensity without getting modified by
the dorsal horn of spinal cord.
•Their descending pain inhibiting
pathways are less developed than in
adults.

55. Sex
Women are more prone, than males, due to difference in
hormonal levels
Emotional status
People in general suffering from depression and anxiety
pain
Smoking
• nicotine reduces body stores of vitamin C,
adversely affects the pain processing
mechanisms of the brain and interacts with
opioid pain medications.
• Trauma
• People who have experienced childhood
injuries and trauma show more pain sensitivity.

56. FACTORS :-
• Weather
• People experience arthritic pain more
during winter season.
• Sleep
• Sleep deprivation increases pain
perception.

57. ELECTROPHYSIOLOGY OF
PAIN

58. Step 1
•Nerve possess resting potential of – 70
mV that exists across the nerve membrane,
produced by ions on either side of the
membrane.
Sodium Potassium pump keeps the
potential by pump in K+ in and Na+ out.

59. Step 2
INITIAL PHASE OF SLOW DEPOLARIZATION. The electrical
potential within the nerve becomes slightly less negative.
• Rapid phase of depolarization
This phase results in a reversal of the electrical
potential across the nerve membrane. Nerve
becomes positive in relation to the outside. An
electrical potential of +40 mV exists inside of the
nerve . Termed as threshold potential or firing
threshold.

60. Step 3
• PHASE OF REPOLARIZATION .
• The electrical potential gradually becomes more negative
inside – 70 m V is again achieved.
• Time required 1 millisecond (msec) depolarization takes 0.3
msec; repolarization takes 0.7 msec

61. PAIN OF UNBORN
• An unborn child at 20 weeks gestation “is fully
capable of experiencing pain. ( EEG Shows) ”

62. CONCLUSION

63. REFRENCES
• INGLE ENDODONTICS 6TH EDITION
• PRINCIPLES OF ANATOMY AND
PHYSIOLOGY,TORTORA,8TH EDITION
• SEMULINGUM PHYSIOLOGY.
• MONHEIMS LOCAL ANESTHETICS AND
PAIN CONTROL IN DENTAL PRACTICE.

64. REFRENCES
• P.D. Wall, R. Melzack, "On nature of cutaneous
sensory mechanisms," Brain, 85:331, 1962.
• R. Melzack, P.D. Wall, "Pain mechanisms: A new
theory," Science, 150:171-9, 1965.
• Kandel, Eric R.; James H. Schwartz, Thomas M.
Jessell (2000). Principles of Neural Science, 4th
edition, New York: McGraw-Hill, 482–486

65. THANKYOU