1. PAIN & THEORIES
OF PAIN
AVANIANBAN CHAKKARAPANI
Lecture 2
Date:12.01.2015
Time:3.00 to 4.00 pm

2. Learning Objective
 To provide knowledge and understating of
a. Pain Definition;
b. Theories of pain(outline) ; and
c. Pain gate theory in detail

3. Learning Outcome
 Able to explain meaning of pain, theories of pain
 Able to describe ‘ GATE CONTROL THEORY ’

4. PAIN MEANING/DEFINITION
 In 1968 McCaffery defined pain
as “whatever the experiencing
person says it is, existing
whenever he/she says it does”
 In 1979 IASP defined pain as
“unpleasant sensory and
emotional experience
associated with actual or
potential tissue damage, or
described in terms of
suchdamage.”
 Pain from poena --->
Latin means punishment.

5. CLASSIFICATION OF PAIN
Nociceptive
Neuropathic
Psychogenic

6. TYPES OF PAIN FIBRES
TYPE OF
NERVE
CONDUCTION
VELOCITY
( MTS/SEC )
MELINATED TYPE OF PAIN
A- DELTA 20 (fast) YES SHARP, PRICKING,
WELL LOCALIZED
C 1 (slow) No DULL ACHE,
DIFFUSE

7. Picture with
Caption
Layout
 Caption

8. DIFFERENT THEORIES OF PAIN
 Intensive Theory (Erb, 1874) ...
 Specificity Theory (Von Frey, 1895) ...
 Strong's Theory (Strong, 1895) ...
 Pattern Theory. ...
 Central Summation Theory (Livingstone, 1943) ...
 The Fourth Theory of Pain (Hardy, Wolff, and Goodell, 1940s) ...
 Sensory Interaction Theory (Noordenbos, 1959) ...
 Gate Control Theory (Melzack and Wall, 1965) √

9. PAIN MODULATION
GATE CONTROL THEORY
(WALL AND MELZACK 1965 )

10. GATE THEORY
 A gating mechanism exists within the dorsal horn of the spinal cord.
 Small nerve fibers (pain receptors)
 large nerve fibers ("normal" receptors)
 These two fibere synapse on projection cells (P), which go up the
spinothalamic tract to the brain, and inhibitory interneurons (I) within the
dorsal horn.
 The interplay among these connections determines when painful stimuli go
to the brain

11. GATE THEORY
 When no input comes in,
the inhibitory neuron
prevents the projection
neuron from sending
signals to the brain (gate
is closed).

12. GATE THEORY
 Normal somatosensory input
happens when there is more
large-fiber stimulation (or
only large-fiber stimulation).
Both the inhibitory neuron
and the projection neuron are
stimulated, but the inhibitory
neuron prevents the
projection neuron from
sending signals to the brain
(gate is closed).

13. GATE THEORY
 Nociception (pain
reception) happens when
there is more small-fiber
stimulation or only
small-fiber stimulation.
This inactivates the
inhibitory neuron, and
the projection neuron
sends signals to the brain
informing it of pain (gate
is open).