pain and its pathway

1. PAIN AND IT’S PATHWAY
PRESENTED BY:
SOUMYA MISHRA
P.G (OMFS)

2. CONTENTS
• DEFINITION
• HISTORY
• BENEFITS OF PAIN
• TYPES OF PAIN
• PROPERTIES
• THEORIES OF PAIN
• PAIN RECEPTORS
• SENSORY NEURONS
• SPINOTHALAMIC TRACT
• INHIBITION OF PAIN
• TENS
• REFERENCES

3. DEFINITION
“ An unpleasant sensory and emotional experience
associated with actual or potential tissue damage
or described in terms of such damage.”
- IASP
“ An unpleasant emotional experience usually
initiated by a noxious stimulus and transmitted
over a specialized neural network to the central
nervous system where it is interpreted as such.”
- Monheim

4. HISTORY
 Latin word ‘poena’ – punishment from God.
Aristotle - first to distinguish 5 physical senses
and considered pain to be the ‘passion of the
soul’
 Plato – contented pain and pleasure arose
from within the body.

5. Benefits of pain sensation
 Pain gives us warning signal about the
problems.
 Pain prevents further damage
 Pain urges the person to take proper
treatment to prevent major damage.

6. TYPES OF PAIN
• Types of pain sensation
• 1) Fast pain
• 2) Slow pain
• 3) Deep pain

8. OROFACIAL PAIN CLASSIFICATION
(OKESON)
• AXIS I (physical conditions)
1. Somatic pain
• A. Superficial Somatic pain
a. Cutaneous pain
b. Mucogingival
• B. Deep Somatic Pain
a. Muscle pain
b. TMJ pain
c. Osseous pain
d. Periodontal pain
2. Visceral pain
a. Pulpal pain
b. Vascular pain
c. Neurovascular pain
d. Visceral mucosal pain
e. Glandular, ocular, auricular pain
AXIS II (psychologic
conditions)
1. Mood disorders
2. Anxiety disorders
3. Other conditions
a. Psychologic factors
affecting a medical
condition

9. PROPERTIES
• Excitability
• Adaptation
• Localization
• Effect of strength of stimulus
• Quality or modality of sensation

10. Few facts of pain
 The pain threshold of the skin of a human
subject, determined by electrical stimulation,
is almost the same throughout the body, but
the face and neck exhibit the relatively lowest
values (Notermans, 1966).
 There is no appreciable difference between
the threshold values of the right and left side
of the human body, nor any diurnal variation
(Notermans, 1966).,

11. • Age and sex do not seem to influence the
pain threshold (Hardy, Wolff & Goodell, 1943),
but the pain tolerance of females may be
lower than that of males, (Notermans &
Tophoff, 1967).

12. Theories of Pain
• Pain theories are proposed to offer the
possible physiologic mechanisms involved in
pain. They are as follows
Specificity theory
 Intensity theory
 Pattern theory
Gate control theory

13. Specificity Theory
• Postulated by
Johannes Muller in
1842
• This theory states pain
as separate modality
evoked by specific
receptors that
transmit information
to pain centres or
regions in the
forebrain where pain
is experienced.

14. Pattern Theory
 Postulated by Goldscheider,1894
• Pain receptors share endings or
pathways with other sensory
modalities but different patterns
of activity of the same neurons
can be used to signal painful and
non – painful stimuli
•Eg. Light touch applied to skin
would produce the sensation of
touch and intense pain pressure
would produce pain through high
frequency firing of the same
receptor

15. THE GATE CONTROL THEORY
The theory was proposed by Melzack &
Wall,1965.
This theory of pain takes into account the
relative input of neural impulses along large
and small fibers.

16. The substantia gelatinosa cells terminate on
the smaller nerve fibers just as the latter are
about to synapse, thus reducing activity, the
result is, ongoing activity is reduced or
stopped – gate is closed.
The theory also proposes that large diameter
fiber input has ability to modulate synaptic
transmission of small diameter fibers within
the dorsal horn.
 The large nerve fibers have collateral
branches, which carry impulses to substantia
gelatinosa where they stimulate secondary
neurons.

17. Factors which influence the 'opening
and closing' of the gate
• The amount of activity in the pain fibers.
• The amount of activity in other peripheral fibers -
fibers that carry information about harmless
stimuli or mild irritation, such as touching,
rubbing, or lightly scratching the skin.
• Messages that descend from the brain. Neurons
in the brainstem and cortex have efferent
pathways to the spinal cord, and the impulses
they send can open or close the gate.

19. PAIN RECEPTORS
Sensory Receptors : At the distal terminals are the
afferent (sensory) nerves, specialized sensory
receptors that respond to physical or chemical
stimuli.
Once these receptors are adequately stimulated,
an impulse is generated in the primary afferent
neuron that is carried centrally into the CNS.
Classified in 3 main groups: 1. Exteroreceptors 2.
Proprioceptors 3. Interoreceptors

20. EXTEROCEPTORS
Stimulated by immediate external environment.
Provide information from the skin and mucosa.
Examples:
1. Merkel’s corpuscles ( tactile receptors in the
submucosa of tongue)
2. Meissner’s corpuscles: tactile receptors in skin
3. Free nerve endings: perceive superficial pain and
touch

21. PROPRIOCEPTORS
 Provide information from the musculoskeletal
structures concerning the position and movement of
the body.
 Automatic functioning
 Examples:
1. Muscle spindles: mechanoreceptors found between
skeletal muscle fibres.
2. Golgi tendon organs: mechanoreceptors in the
tendons of muscles signal muscle tension
3. Periodontal mechanoreceptors respond to
biomechanical stimuli

22.  Proprioception, which refers tooth position and
movement of the limbs (kinaesthesia), is
determined by mechanoreceptors located in skin,
joint capsules and muscle spindles.
The CNS integrates information received from
these receptors, while keeping track of previous
motor responses that initiated limb movement –
a process known as efferent copy or corollary
discharge (reviewed by Matthews, 1982).

23. INTEROCEPTORS
Located in and transmit impulses from viscera
of the body.
Examples: Free nerve endings: perceive
visceral pain and other sensations.

24. Nociceptor
Sensory input from various stimuli (either
external or internal) is received by specific
peripheral receptors, called as nociceptors.
Nociception – responds as transducers and
transmit impulses.
Perception of pain.
Found in all areas of body.
External nociceptors – skin, cornea and
mucosa

25.  Internal nociceptors – muscle, joint, bladder,
gut and continuing along the digestive tract.
Cell bodies of these neurons are located in
either the dorsal root ganglia or the trigeminal
ganglia.
Trigeminal ganglia are specialized nerves for
the face, whereas the dorsal root ganglia
associate with the rest of the body.

26. Development of Nociceptors
Develop from neural crest stem cells.
Neural crest cells are responsible mainly for
development of the peripheral nervous
system.
Cells split off from the neural tube as it closes,
and nociceptors grow from the dorsal part of
this neural crest tissue.
Forms late during neurogenesis.

27. Sensory neurons
• FIRST ORDER NEURONS (POSTERIOR NERVE ROOT
GANGLIA)
• SECOND ORDER NEURONS (SUBSTANTIA
GELATINOSA
• THIRD ORDER NEURONS (THALAMIC NUCLEUS,
RETICULAR FORMATION, TECTUM, GREY
MATTER)
SOMATOSENSORY
CORTEX

29. FIRST ORDER NEURON
 The substantia gelatinosa
cells terminate on the
smaller nerve fibers just as
the latter are about to
synapse, thus reducing
activity, the result is,
ongoing activity is reduced
or stopped – gate is closed.
 The theory also proposes
that large diameter fiber
input has ability to modulate
synaptic transmission of
small diameter fibers within
the dorsal horn

30. SECOND ORDER NEURON
The primary afferent neuron
carries impulse into the CNS and
synapses with the second-order
neuron.
This second-order neuron is
sometimes called a transmission
neuron since it transfers the
impulse on to the higher centers.
The synapse of the primary
afferent and the second-order
neuron occurs in the dorsal horn of
the spinal cord.

31. THIRD ORDER NEURON
 Cell bodies of third order
neurons of the
nociception-relaying
pathway are housed in –
1. The ventral posterior lateral
nuclei
2. The ventral posterior
inferior nuclei
3. The intralaminar thalamic
nuclei
 Third order neuron fibers
from the thalamus relay
thermal sensory
information to the
somatosensory cortex

32. Lateral Spinothalamic tract
 It is also called the lateral
spinothalamic fasciculus
 It carries pain and
temperature sensory
information (protopathic
sensation) to the
thalamus
 It is composed primarily
of fast-conducting,
sparsely myelinated A
delta fibers and slow-
conducting,
unmyelinated C fibers

33.  From the site of pain
generation(from the
periphery) the pain
senses are carried by Aδ
& C fibres
 Their cell bodies are
situated in the dorsal
root ganglion.
 The central processes of
the neuron, lying in the
‘sensory root’ of the
spinal nerve enter the
dorsal horn to terminate
in the SGR ( Substantia
gelatinosa Rolandi),
situated in the tip of
dorsal horn.

34. From the SGR, 2nd
order neuron arises,
decussates and then
moves up through the
white matter of spinal
cord to reach the brain
These secondary
neurons are situated in
the posterior horn,
specifically in the
Rexed laminae regions
I,II, IV, V and VI.

35.  At SGR, there is a synapse
between 1st order & 2nd
order neuron. Also there is
synapse of 2nd & 3rd
order neuron at thalamus
 The neurotransmitter at
the synapse between Aδ
fiber & 2nd order neuron
at SGR is glutamate while
the NT between C fiber &
2nd order neuron (slow
pain) at SGR is substance
P.

36.  The primary somatosensory
cortex is located in the
postcentral gyrus, and is part
of the somatosensory
system
 Conventionally, areas 3,1,2
have been regarded as the
primary somatosensory
cortex
 Recent studies by Kaas has
shown that only area 3
should be referred to as
"primary somatosensory
cortex", as it receives the
bulk of the thalamocortical
projections from the sensory
input fields

37. DUAL PAIN PATHWAY

38. Neospinothalamic Tract for Fast Pain
The fast type A(δ) pain
fibers transmit mainly
mechanical and acute
thermal pain
They terminate mainly
in lamina I at the dorsal
horn and these excite
second order neurons of
the neospinothalamic
tract

39. Paleospinothalamic tract for Slow Pain
This pathway transmits
pain mainly from
peripheral slow chronic
Type C pain fibers
In this pathway, the
peripheral fibers
terminate almost
entirely in lamina II and
III of dorsal horns of
spinal cord, together
called as substantia
gelatinosa

40. INHIBITION OF PAIN
• Pain sensations may be controlled by interrupting
the pain impulse between receptor and
interpretation centers of brain
• This may be done by medicinal, surgical or by
other approaches
• Most pain sensations respond to pain reducing
drugs/analgesics which in general act to inhibit
nerve impulse conduction at synapses
• Occasionally however, pain may be controlled
only by surgery.

41. Medicinal approach
 NSAIDS -
 Ibuprofen
 Naproxen
 Aspirin
 ketorol
 Opiods -
 Codeine
 Hydrocodone
 tramadol

42. Surgical Approaches
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

43. Transcutaneous Electrical Nerve
Stimulation (TENS)
• With TENS, cutaneous bipolar
surface electrodes are placed in the
painful body regions and low
voltage electric currents are passed
• Best results have been obtained
when intense stimulation is
maintained for at least an hour daily
for more than 3 weeks
• TNS portable units are in wider
spread use in pain clinics
throughout the world and has been
proved most effective against
neuropathic pain

44. • Bell`s ‘Orofacial pain’, 5th edition, Jeffrey P.
Okeson
• Text book of Medical Physiology, 10th edition,
Arther C Gyton
• Textbook of physiology ,sembulingum
• Text book of ‘Oral medicine’- 10th edition,
Burkett’s
• INTERNET..