basic knowledge of Pain

1. PHYSIOLOGY OF PAIN
By
Lalita Verma
Under Guidance of
Dr. P. K. Shukla
STATE LAL BAHADUR SHASTRI HOMEOPATHIC MEDICAL COLLEGE & HOSPITAL
PRAYAG RAJ

2. CONTENTS
• Introduction and Definition
• Classification of Pain
• Pain Receptors
• Fibres of Transmission
• Theories of Pain
• Pain Pathway
• Tracts Conveying Pain Sensation
• Perception of Pain
• Modulation of Pain
• Factors Affecting Pain
• Applied Physiology

3. Introduction and Definition
• Pain is derived from latin “Poena” meaning punishment from God.
• Sherrington defined pain as “The psychical (=pertaining to mind) adjunct (joined to)
of an imperative (urgent) protective reflex” i.e. pain is a sensation which draws
attention of the individual as a whole.
• According to IASP –Pain is unpleasant sensory and emotional experience associated
with actual or potential tissue damage or described in term of such damage.
• Pain is most fundamental and primitive sensation which
may be observed more or less all over the body.

4. • It is protective in nature and always indicates some serious trouble in the
locality such as a structural damage or some sort of serious functional or
metabolic derangement.
• Naked nerve ending are presumably the sense organs for pain and are
distributed all over the body.

5. Classification of Pain
According to
International Association
for the study of Pain in
1944
Clifford J. Woolf &
others
Physiological
basis

6. According to IASP(1944)
Classified pain according to specific characteristics .
• Region of the body involved (e.g. abdomen, lower limbs)
• System whose dysfunction may be causing the pain(e.g. nervous ,
gastrointestinal)
• Duration and pattern of occurrence.
• Intensity and time since onset.
• Cause.

7. Acc. To Clifford J. Woolf
& other
Nociceptive
Pain
Inflammator
y Pain
Pathological
Pain
Neuropathic
pain
Dysfunction
pain

9. Physiological Basis
Superficial Pain Deep Pain Visceral Pain
• Activation of nocicepters in the
skin or other superficial tissue .
• Stimulation of nocicepters in
bones ,blood vessels fasciae ,
tendon muscle & hollow
viscera .
• It involves gut & hollow viscera
.
• Sharp , well defined & clearly
located .
• Dull aching , poorly localized
,deep somatic pain.
• Diffused ,poorly localized
because pain receptor are
relatively few .
• It leads to reflex withdrawal
movements ,increase in heart
rate ,BP & respiration .
• It produces faintness , nausea
,vomiting, sweating,
bradycardia & fall in BP .
• It may be accompanied by
symptoms like nausea ,
vomiting etc.
• It usually does not radiate. • It is both local & radiates to the
distant site .
• It tends to radiate from the
initial location to involve other
areas of the body as well.

10. Pain Recepter
Sensory receptors
Somatic recepter
Visceral recepter
Special recepter
Nociceptors
Mechanoreceptors

11. Pain Recepter
• Somatic receptor – It included Touch , Thermal , Pressure etc.
• Visceral receptor – Baroreception , Chemoreception etc.
• Special receptor – visual , Audition , Olfaction , Gustation etc.
• Nocicepter – A nerve ending that responds to noxious stimuli that can
actually or potentially produce tissue damage .
• These substances include histamine , serotonin , Bradykinin , Acetylcholine
etc .
• Mechanorecepter – Which respond to tectile non-painful stimuli can be
assessed psychophysically by the ability of a human subject to discriminate
whether application of a two blunt point stimuli is perceived as one or two
part .

12. Fiberes for
Transmission
Aẟ Fibre C Fibre
 Mylinated  Unmylinated
2-5µm in diameter  0.4-1.2µm in diameter
 Fast fibre  Slow fibre
 Higher conduction velocity (12-30
m/s)
Slow conduction velocity (0.5-2 m/s)

13. Theories of Pain
Specificity
theory
Pattern
theory
Dermatomal
theory
Gate control
theory
Referred Pain Influence of
dermatomal
theory
Theorises of
convergence
and
facilitation
Theory of
facilitation

14. Specificity Theory
Von Frey (1895) argued that the body has a seprate sensory system for
perceiving pain –just as it does for hearing and vision and this system contains
its own special recepters for detecting pain stimuli,its own area of the brain for
processsing pain signals.
Pattern Theory
Goldschneider (1920) proposed that the recepters for pain are
shared with other senses , such as of touch and there is no separate
system for perceiving pain .

15. Dermatomal Theory of Pain
• Referred pain- Pain arising from the viscera is often referred to that
region of body surface which is supplied by the posterior root of the
same spinal segment.
• Influence of Dermatomal Rule- When pain is referred it is usually to a
structure that developed from the same embryonic segment or
dermatome as the structure in which the point originates.
• Convergence and facilitation- This theory holds that
somatic and visceral afferents converges on the
same spinothalmic neuron.

16. Theory of facilitation-
This theory holds that owing to the
effects of subliminal fringe, the
incoming impulses from viscera lowers
the threshold of spinothalamic neurons
receiving afferents from somatic area so
that minor activity in the pain pathways
from somatic areas (activity which
would commonly die out in the spinal
cord) passes onto the brain.

17. Gate Control
Theory
• Ronald Melzack & Patrick Wall in
1965 decribed how non-painful
sensation can override and reduce
painful sensation.
• Simultaneous stimuli coming from
large sensory fibres such as tectile
fibre reduces the transmission of
pain signals. This is because dorsal
horns of spinal cord act as gates
which control the entry of pain
signals in presence of excessive
tectile signals.

18. Mechanism of Gate control Theory
Step by step –
 Pain fibre &Tectile fibre simultaneously comes to Rexed lamina Ⅱ of dorsal
horn 1.Pain fibre anastmos with substantia gelatinosa.
2.Tectile fibre ascend up but gives a little collateral.
 These little collateral stimulate inhibitory neuron ( Interneuron).
 These inhibitory neurons start releasing certain chemical like GABA .
 GABA inhibit the Substantia gelatinosa by closing their calcium channel .
 Due to closing of channel of substantia gelatinosa releasing less substance p or
Glutamate neurotransmitter.
 So decrease the Action Potential of pain information which decrease severity of
pain .
 We experience less pain.

19. Pain Pathway
Transmission of pain sensation occurs in 3 stages.
1. Impulses are transmitted from the site of transduction
along the nociceptor fibres to the dorsal horn in the
spinal cord.
2. Impulses from the spinal cord are relayed to the
brain stem.
3. Impulses are carried and relayed through
connections between the thalamus, cortex
and higher level of the brain.

20. Tracts Conveying Pain Sensation
Neospinothalmic Pathway
Impulses via
Spinothalmic tract
Paleospinothalmic
Pathway
Impulses via
Spinoinoreticular tract

21. Tract Conveying Pain Sensation
1). Neospinothalmic Pathway- Pain pathway by Aẟ fibre is called
neospinothalamic pathway.
• It carries information to the midbrain, thalamus and post central
gyrus where pain is perceived.
2). Paleospinothalmic pathway- Pain pathway by C fibre is called
Paleospinothalmic pathway.
• It carries information to reticular information to the reticular
formation, pons, limbic system and mid brain.

22. Perception of pain
• Perception of pain is the end result of the neuronal activity of pain
transmission and where pain becomes a conscious multidimensional
experience.
• When the painful stimuli are transmitted to the brain stem &
thalamus, multiple cortical areas are activated & responses are
elicited.
• These cortical areas are-
1. The reticular system.
2. Somatosensory cortex.
3. Limbic system.

23. Modulation of pain
Descending pain inhibitory pathway: Pain is
modulated via descending modulatory pain
pathways (DMPP).
They inhibit afferent pain signal.
• Pain afferents stimulates the neurons (PAG)
this result in activation of efferent nociceptive
pathway Release norepinephrine and 5-
HT Stimulation of little inhibitory neuron
(Interneuron) Secretion of endogenous
opioids (Enkephalins, Endorphins) Inhibit
substantia gelatinosa to decrease sending
action potential Less action potential sent
upto the system so less pain perception.

24. Facter affecting Pain
• Emotional status.
• Fatigue.
• Age.
Applied Physiology of Pain
1. Analgesia- Loss of pain sensation.
2. Hyperalgesia- Increased sensitivity to pain sensation.
3. Paralgesia- Abnormal pain sensation is called Paralgesia.
*Special Points for relieving pain*
• Soldiers wounded in the heat of bottle may feel no pain until the battle is over.
• Touching or shaking an injured area, decreases the pain of injury.
• Acupuncture has been used to relieve pain.
• Counterirritants.
• Transcutaneous electrical nerve stimulations.

25. Conclusion
• Pain is bad, but not feeling pain can be worse.
• Individuals with a congenital absence of pain receptors are extremely
rare but not unknown. Such individuals are very poor at avoiding
accidental injuries, and often inflict mutilating injuries on themselves.
• As a result, their life span is usually short. Thus pain, although
unpleasant, is a protective sensation with enormous survival value.
• Pain is multidimensional experience involving both the sensation
evolved by noxious stimuli but also the relation to it.
• The sensation of pain therefore depends in part on the patient past
experience, personality and level of anxiety.