1.
PAIN PATHWAY
PRESENTED BY:
DR. AMITHA PRAKASH
POST GRADUATE
STUDENT

2.
1. INTRODUCTION
2. DEFINITIONS
3. HISTORY
4. GLOSSARY
5. CLASSIFICATION OF PAIN
6. MECHANISM OF NERVE TRANSMISSION
7. PAIN PATHWAY
10. THEORIES OF PAIN
11. CLINICAL CONSIDERATION
12. METHODS TO CONTROL PAIN
13. CONCLUSION
14. REFERENCES
CONTENTS

3.
INTRODUCTION
• Pain is almost an universal experience.
• SUBJECTIVE sensation.

4.
DEFINITIONS
An unpleasant
sensory or
emotional
experience
associated with
actual or potential
tissue damage or
described in terms
of damage.
IASP Definition
The subject’s conscious
perception of modulated
nociceptive impulses that
generate an unpleasant
sensory & emotional
experience associated with
actual or potential tissue
damage, or described in
terms of such damage.
Bell’s Orofacial Pain 5th ed
Pain is defined as 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’s Local anesthesia
& pain control in dental
practice. 7th ed

5.
 Derived from Latin -“Poena” meaning Penalty/punishment from God.
 JCAHO declared pain as fifth vital sign (1999).
HISTORY

6.
GLOSSARY OF PAIN
ALLODYNIA
ANALGESIA
ANAESTHESIA DOLOROSA
DYSAESTHESIA
HYPERALGESIA
PARESTHESIA
NEURALGIA
NEURITIS
PAIN THRESHOLD

7.
CLASSIFICATION OF PAIN
• Based on duration
 Acute Pain
 Chronic pain
• According to intensity
 Mild pain
 Moderate pain
 Severe pain
• According to onset
 Spontaneous
 Induced

8.
• According to temporal relationship and duration
 Intermittent
 Continuous
 Protracted
 Intractable
 Recurrent

9.
• According to pain location
 Localized
 Diffused
 Radiating
 Lancinating
 Migrating

10.
CLASSIFICATION OF PAIN(BASED ON ORIGIN)
PAIN
SOMATIC VISCERAL
SUPERFICIAL
DEEP

11.
• Results from stimulation
of the pain receptors in
the tissues.
• Superficial pain- from
skin and subcutaneous
tissues.
• Deep pain-from
muscles, bones, joints,
and periosteum.
• Arises from viscera
• From the heart –Angina
pectoris
• Stomach –peptic ulcer
• Intestine –intestinal
colic,renal colic
SOMATIC PAIN VISCERAL PAIN

12.
FAST PAIN
• Begins after 1 sec or more
and then increases slowly
over many sec or min
• It can occur both in the
skin and in almost any
deep tissue or organ
• Associated with tissue
destruction
• Transmitted by C-fibres
,neurotransmitter –
substance p
SLOW PAIN
• Felt within about 0.1 sec
after a painful stimuli
• Felt mainly in skin not
felt in most deeper
tissues of the body
• Transmitted by A delta
fibres,neurotransmitter –
glutamate

13.
BASIC STRUCTURE OF NEURONS

14.
Depending on function
Sensory Neuron
Motor Neuron
Depending on length of axons
Golgi type 2 neurons
Golgi type 1 neurons

15.
MECHANISM OF NERVE TRANSMISSION

16.
ELECTROCHEMISTRY OF NERVE CONDUCTION
 RESTING STATE
1. Slightly permeable to Na+ ions
2. Freely permeable to K+ & Cl- ions
 MEMBRANE EXCITATION
a) Depolarization
 Excitation of nerve increases permeability to sodium ions
 influx of Na+ ions into nerve cell body- depolarization- -50 to -60mv
 Decrease in negative electrical potential -55mv – firing threshold
 When firing threshold is reached – rapid influx of Na+ ions – electrical
potential of +40mv
 This takes place within 0.3 msec.

17.
b) Repolarization
 Action potential terminates – membrane repolarizes
 Due to inactivation of permeability to Na+ ions.
 Increased permeability of K+ ions – efflux of K+ ions – rapid
repolarization occurs.
 Returns to resting potential
 Movement of Na+ - depolarization & movement of K+ ions –
repolarization – passive.
 After reaching resting membrane potential – slight excess of Na+ ions
& K+ions
 Period of metabolic activity
 Process requires 0.7 msec.

18.
THEORIES OF PAIN
1. Intensity theory - PLATO
2. Specificity theory - VON FREY -1895
3. Pattern theory - JP NAFE
4. Gate control theory - RONALD MELZACK and
5. PATRICK WALL-1965

19.
Intensity Theory
• Fourth century by Plato
• The theory defines pain, not as a unique sensory experience but rather, as an
emotion that occurs when a stimulus is stronger than usual.
• This theory is based on Aristotle’s concept that pain resulted from
excessive stimulation of the sense of touch.

20.
Limitation
•The trigeminal system provides an example against this theory.
•In case of trigeminal neuralgia the patient can suffer excruciating pain
from a stimulus no greater than a gentle touch provided it is applied to a
trigger zone.
•Although, the intensity theory is not accepted, it remains true to say that
intensity of stimulation is a factor in causing pain.

21.
Specificity Theory (Von Frey, 1895)
• Specific pain receptors transmit signals to a "pain center" in
the brain that produces the perception of pain.
• This theory considers pain as an independent sensation with
specialized peripheral sensory receptors [nociceptors], which
respond to damage and send signals through pathways (along
nerve fibres) in the nervous system to target centers in the
brain.
• These brain centers process the signals to produce the
experience of pain.

22.
Specificity theory cannot explain
•Any pathologic pain produced by mild noxious stimuli.
• Referred pain that can be triggered by mild innocuous
stimulation of normal skin.
•Does not explain the paroxysmal episodes of pain produced
by mild stimulation of trigger zone in trigeminal neuralgia.

23.
PATTERN THEORY
• In 1894, Goldscheider proposed that stimulus intensity and central
summation are the critical determinant of pain.
• Particular pattern of nerve impulses that evoke pain are produced
by summation of sensory input within the dorsal horn of spinal cord
(J.P. Nafe, 1929)
• Pain results when the total output of the cells exceed a critical level.

24.
• RONALD MELZACK and PATRICK WALL in 1965
GATE CONTROL THEORY

25.
SIGNIFICANCE OF GATE CONTROL
The gating of pain at spinal level is similar to presynaptic
inhibition. It forms the basis for relief of pain through
• rubbing
• massage techniques
• application of ice packs
• Acupuncture
• Electrical Analgesia .
All these techniques relieve pain by stimulating the release of
endogenous pain relievers ( opioid peptides ) which close the
gate and block the pain signals.

26.
REFERRED PAIN
• Referred pain is the pain that is perceived at a site adjacent to or
away from the site of origin.
• The pain usually is initiated in one of the visceral organs are
referred to an area on the body surface.
• The pain may be referred to an area of the body not exactly
coincident with the location of the viscus producing the pain.
• For eg,
a) Cardiac pain is felt at the inner part of left arm and left shoulder.
b) Pain in diaphragm is referred to right shoulder

27.
MECHANISM OF REFERRED PAIN
Dermatomal Rule
• According to it, pain is referred to a structure, which is developed from the
same dermatome from which the pain producing structure is developed.
• A dermatome includes all the structures or parts of the body, which are
innervated by afferent nerve fibers of one dorsal root. For example, the
heart and inner aspect of left arm originate from the same dermatome. So,
the pain in heart is referred to left arm.

28.
VISCERAL PAIN
• A striking characteristic of the brain is that although it receives and
processes nociceptive information, the brain itself has no sensation of
pain.
• The visceral organs themselves have no pain receptors, pain receptors
are present , embedded in the walls of the arteries serving these organs.

29.
• Visceral pain is characterized as diffuse and poorly localized and is
often “referred to” and felt in another somatic structure distant or
near the source of visceral pain.
• General visceral afferent nociceptive information from visceral
structures of the trunk is carried mostly by type C, Aδ, or Aβ fibers

30.
NEURAL PAIN PATHWAY
• Nociception is the neural mechanism by which an individual detects the
presence of potentially tissue harming stimulus .
• Nociceptive mechanism consists of:
• Transduction
• Transmission
• Modulation
• Perception

31.
TRANSDUCTION
• Involves conversion of signals from the environment , that is, light,
taste, sound, touch smell, into electrical signals.
• These signals are then collected and processed by the CNS.
• Receptors are sensory nerve endings that terminates in the periphery
and produces a series of impulses upon stimulation.
• These impulses are transmitted through afferent nerves.

32.
 There are two different types of receptors:-
1. Exteroreceptors
2. Interoreceptors
 EXTEROCEPTORS are receptors which provides information from skin
and mucosa.
 Eg . Meissner’s corpuscles : tactile receptors in skin
 Merkel’s corpuscles : tactile receptors in the submucosa of oral
mucosa and tongue
 Raffini’s end organ : warmth receptor
 Pacinian corpuscle : pressure receptor
 Krause’s end bulb : cold receptor
 Free nerve ending : perceives superficial pain and touch

33.
 INTEROCEPTORS
 Interoceptors are the receptors which give response to stimuli
arising from within the body.
 For eg,
 Baroreceptors – blood vessels
 Chemoreceptors – GI tract
 Osmoreceptors – urinary tract

34.
TRANSMISSION
MODULATION
PERCEPTION

35.
NEUROTRANSMITTER

36.
CHEMICAL NEUROTRANSMITTERS

37.
Neospinothalamic pathway
• The fast type a-delta pain fibres transmit mainly mechanical
and acute thermal pain.
• They terminate mainly in lamina I (lamina marginalis of the
dorsal horns)
• These give rise to long fibers that cross immediately to the
opposite side of the spinal cord through and then pass
upward to the brain stem in anterolateral columns.

38.
• These fibers terminate in the ventrobasal nucleus in
thalamus. From the thalamic areas, signals are
transmitted to cortex .
• “glutamate” is the neurotransmitter for type A(δ)
pain nerve fiber endings.

39.
Paleospinothalamic pathway
• The peripheral fibres terminate almost entirely in laminas
II and III of the dorsal horns, which together are called as
substantia gelatinosa.
• The paleospinothalamic system transmits pain mainly
carried in the peripheral slow-chronic type-C pain fibres,
although it does transmit some signals from type A-delta
fibers as well.

40.
DENTAL PAIN PATHWAY
• Trigeminal nerve is the mixed cranial nerve
• It is the chief sensory nerve for face and the motor nerve for
muscles of mastication
• Trigeminal nerve carries somatosensory information from face ,
teeth , periodontal tissues , oral cavity and cranial dura mater to
sensory cortex

41.
Origin
• Sensory fibers of trigeminal nerve arise from the
trigeminal ganglion situated near temporal bone.
• Peripheral processes of neurons in this ganglion form
three divisions of trigeminal nerve, namely ophthalmic,
mandibular and maxillary divisions.
• Central processes from neurons of trigeminal ganglion enter pons in
the form of sensory root.

42.
Termination
• After reaching the pons, fibers of sensory root divide into
two groups, namely descending fibers and ascending
fibers.
• Descending fibers terminate on primary sensory
nucleus and spinal nucleus of trigeminal nerve. Primary
sensory nucleus is situated in pons.
• Spinal nucleus of trigeminal nerve is situated below the primary
sensory nucleus and extends up to the upper segments of spinal
cord.
• Ascending fibers of sensory root terminate in the mesencephalic
nucleus of trigeminal nerve, situated in brainstem above the level of
primary sensory nucleus.

43.
Central Connections
• Majority of fibers from the primary sensory nucleus and spinal nucleus of
trigeminal nerve ascend in the form of trigeminal lemniscus and terminate in
ventral posteromedial nucleus of thalamus in the opposite side.
• From thalamus, the fibers reach the somatosensory areas of cerebral cortex.
• Primary sensory nucleus and spinal nucleus of trigeminal nerve relay the
sensations of touch, pressure, pain and temperature from the regions mentioned
above.

44.
• Fibers from mesencephalic nucleus form the
trigeminocerebellar tract that enters spinocerebellum via
the superior cerebellar peduncle of the same side.
• This nucleus conveys proprioceptive impulses from facial
muscles, muscles of mastication and ocular muscles.

45.
CLINICAL CONSIDERATION
PERIODONTAL PAIN
ACUTE GINGIVAL OR
PERIODONTAL ABSCESS
PERICORONITIS

46.
PERIODONTAL PAIN
• Localized, deep throbbing pain
• Involving inflammation of PDL around one or more teeth
• Mobility
• Localized bleeding
• Presence of pocket
• In radiograph loss of bone is present.
• Pain last for hour or day
• Involve tooth is tender on percussion
• If pain involve multiple teeth including opposing teeth then occlusal trauma should considered

47.
ACUTE GINGIVAL OR PERIODONTAL ABSCESS
• Tooth is painful to bite on and is not so deep seated or throbbing as that of apical abscess.
• Pain is spontaneous
• Associated localized swelling
• Presence of deep PDL pocket

48.
PERICORONITIS
• The pain can be severe, radiating in the posterior mouth region.
• The patient mostly faces difficulty or inability to comfortably close or open the mouth.
• The mucosa posterior to the erupting molar is very painful to touch.

49.
Methods of pain control
1) Removing the cause
2) Blocking the pathway of painful impulses
- Local anesthetic solution
- Interferes with pain perception
3) Raising the pain threshold

50.
MEDICATIONS
 Non opioids
• These include aspirin and NSAIDS, which have analgesic, anti-pyretic,
anti-platelet, anti-inflammatory actions.
• They differ from opioid analgesic in that they presumably prevent the
formation of prostaglandin E1 by inhibitory action on enzyme,
cyclooxygenase.
• They don’t produce tolerance, physical dependence or addiction.
• They have ceiling effect where by increases dose beyond peak point
does not increase analgesic effect, but may effect duration of analgesic.

51.
 Opiods
 Includes morphine and morphine like drugs. They act by :-
1. Depressing nociceptive neurons while stimulate non-nociceptive
Cells.
2. It elevates the threshold for painful stimuli.
3. It alters the emotional reaction to pain.
4. It produces sleep which also elevates the threshold.
5. Addition of codeine to NSAIDS increases analgesic effect.

52.
NEW APPROACHES TO INHIBIT PAIN
Transcutaneous Electrical Neural 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 atleast an hour daily for more than 3 weeks.
• TENS portable units are in wider use in clinics throughout the world
and has been proved most effective against neuropathic pain.

53.
ACUPUNCTURE
Method of inhibiting pain impulses.
• Acupuncture theory is based on an invisible system of communication
between various organs of the body that is distinct from circulatory, nervous
and endocrine system.
• Location of needle insertion depends on part of body acupuncturist wishes
to anesthetize.
• Eg : to pull a tooth – a needle is inserted in the web between thumb and
index finger.

54.
Conclusion

55.
 ESSENTIALS OF PHYSIOLOGY SHEMBULINGAM
 MONHEIMS LOCAL ANAESTHESIA AND PAIN CONTROL 7th
EDITION
 BELL’S OROFACIAL PAIN – JEFFREY 6th EDITION
 TEXTBOOK OF PHARMACOLOGY – TRIPATHI 2nd EDITION
 CARRANZA CLINICAL PERIODONTOLOGY 11th EDITION
REFERENCES