Includes - definition of Pain, Components of Pain, Neuron, Nerve fibers, Pain receptors, Pain Pathway, Pain theories, Applied Aspect, References

1. PAIN PATHWAY
PRESENTED BY:
DR GAYATRI MEHROTRA

2. DEFINITION OF PAIN
 The International Association For The Study Of
Pain:
Pain is “an unpleasant sensory and emotional
experience associated with actual or potential tissue
damage, or described in terms of such damage.”
 Monheim:
“ An unpleasant emotional experience usually
initiated by noxious stimulus and transmitted over a
specialized neural network to the CNS where it is
interpreted as such.”

3. COMPONENTS OF PAIN
 Pain sensation has two components:
1) Fast pain
2) Slow pain
Pain stimulus is applied
Bright,sharp ,localized pain
produced( fast pain)
Followed by dull,diffused,unpleasant
pain(slow pain)

4. NEURON: THE BASIC FUNCTIONAL
UNIT

5. SYNAPSE
 The junction between two neurons is called synapse.
 The main function of the synapse is to transmit the
impulses.

7. Transmission Of Impulse

8. NERVE FIBERS
Fiber type Function Diameter
(um)
Velocity
(m/s)
1) A-alpha Motor, muscle
proprioception
12 to 20 70 to 120
2) A-beta Touch, pressure,
proprioception
5 to 12 30 to 70
3) A-gamma Touch , motor
proprioception
5 to 12 30 to 70
4) A-delta Pain, temperature,
pressure proprioception
1 to 4 12 to 30
5) B Preganglionic autonomic
activity
1 to 3 14.8
6) C Pain,temp,pressure,
postganglionic activity
0.5 to 1 2

10. PAIN RECEPTORS:
NOCICEPTORS
 A nerve ending that responds to noxious stimuli that
can actually or potentially produce tissue damage.
 Receptors for fast pain are sensitive to mechanical or
thermal stimuli of noxious strength.
 Receptors for slow pain are sensitive not only to
mechanical or thermal stimuli but also to a wide
variety of chemicals associated with inflammation.

11. bradykinin histamine serotonin
acetylcholine
Hydrogen and
potassium ions

13.  Since the pain receptors respond to a wide variety
of stimuli, they are called polymodal.
 Impulses from nociceptors are transmitted via two
fiber types:
1) Myelinated A delta fibers
2) Unmyelinated C fibers

15. A delta - fibers C -fibers
1) Myelinated 1) Unmyelinated
2) 2-5 um in diameter 2) 0.4-1.2 um in diameter
3) Rate of 12-30 m/s 3) Rate of 0.5-2 m/s
4) Threshold is medium 4) Threshold is high
5)Carry fast pain sensation 5) Carry slow pain sensation

16. SENSORY NEURONS
First order
neuron
Second order
neuron
Third order
neuron

18. FIRST ORDER NEURON
 First order neurons are the cells in the posterior
nerve root ganglia.
 These neurons receive impulses from the pain
receptors through their dendrites and their axons
reach the spinal cord.
 A-delta fibers then synapse with marginal cells in
the posterior gray horn.
 C type fibers synapse with substantia gelatinosa

19. SECOND ORDER NEURON
 Marginal cells and the cells of substantia gelatinosa
form the second order neurons.
Fibers of
marginal cells
Fibers of
substantia
gelatinosa
Form neospinothalamic
tract
Form
paleospinothalamic
tract
Terminate in posterolateral ventral
nucleus of thalamus

22. THIRD ORDER NEURON
 The third order neurons of pain pathway are the
neurons of thalamic nucleus, reticular formation,
tectum and gray matter around aqueduct of Sylvius

23. PAIN PATHWAY

24.  On entering the spinal cord, the pain signals take
two pathways to the brain , through
1) Neospinothalamic tract
2) Paleospinothalamic tract

25. NEOSPINOTHALAMIC TRACT
A delta fibers transmit fast pain
Terminate in lamina marginalis of dorsal horn
Excite second order neurons of neospinothalamic tract
Cross to opposite side of cord
Turn upward passing to the brain

26.  It is believed that glutamate is the neurotransmitter
substance secreted in the spinal cord at the A-delta
pain nerve endings.
 This is one of the most widely used excitatory
transmitters in the central nervous system, usually
having a duration of action lasting for only a few
milliseconds.

27. PALEOSPINOTHALAMIC TRACT
C type fibers transmit slow pain
Terminate in lamina II and III(substantia gelatinosa)
Join the fibers from the fast pain pathway
Cross to opposite side of cord
Then upward to the brain

28.  Type C fibers entering the spinal cord release both
glutamate transmitter and substance p transmitter.
 It has been suggested that the "double" pain
sensation, one feels after a pinprick might result
partly from the fact that the glutamate transmitter
gives a faster pain sensation, whereas the
substance P transmitter gives a more lagging
sensation.

30. PAIN PATHWAY OF MAXILLOFACIAL
REGION
 The fifth cranial nerve or Trigeminal nerve is the
principal sensory nerve of the head region.
 Any stimulus in area of trigeminal nerve is received by
both myelinated and nonmyelinated fibers and
conducted as an impulse
along the afferent fibers
of ophthalmic, maxillary
and mandibular branches
into semilunar or
gasserian ganglion.

32. PAIN THEORIES
 Specificity theory:
 Descartes in 1644 - pain is conceived as a straight channel
from skin to brain.
 Pattern theory:
 In 1894, Goldscheider was the first to propose that
stimulus intensity and central summation are the critical
determinants of pain.

33.  Gate control theory:
 Proposed by Melzack and Wall in 1965.
 It postulates the following:
 Information is transmitted to CNS by
small peripheral nerves.
 Cells in spinal cord which are excited by these injury
signals are also facilitated or inhibited by other large
peripheral nerves that also carry information.
 Descending control systems modulate the excitability of
cells that transmit information about injury.

34. APPLIED PHYSIOLOGY
 Hemisection of spinal cord: Brown- Sequard
syndrome:

35.  Hyperalgesia:
 A pain pathway sometimes becomes excessively
excitable that give rise to hyperalgesia, which
means hypersensitivity to pain.
 causes : 1) excessive sensitivity of the pain
receptors
2) facilitation of sensory transmission

36.  Thalamic syndrome:
 In this syndrome, there is damage to posterior
thalamic nuclei , usually caused by obstruction of
branch of posterior cerebral artery.
 Patients with this syndrome have attacks of
prolonged, severe and extremely unpleasant pain.

37.  Herpes zoster ( shingles ):
 Occasionally a herpes virus infects a dorsal root
ganglion which causes severe pain in the dermatomal
segment normally subserved by the ganglion , thus
eliciting a segmental type of pain that circles halfway
around the body.

38.  Trigeminal neuralgia:
 Lancinating pain occurs in some people over one side
of the face in the sensory distribution area of
trigeminal nerve
 Pain feels like sudden electric shock and it may
appear for only a few seconds at a time or may be
almost continuous.

39.  Wallenberg syndrome:
 A stroke usually affects only one side of the body.
 If a stroke causes loss of sensation, the deficit will be
lateralized to the right side or the left side of the body.
 The only exceptions to this rule are certain spinal cord
lesions and the medullary syndromes, of which
Wallenberg syndrome is the most famous example.
 In Wallenberg syndrome, a stroke causes loss of
pain/temperature sensation from one side of the face
and the other side of the body.

41. REFERENCES
1) Essentials of medical physiology 3 edition - K
Sembulingam, Prema Semulingam
2) Ganongs review of medical physiology 23 edition- Kim
E Barrett, Susan M Barman, Scott Boitano, Heddwen
L Brooks
3) Guyton and Hall textbook of medical physiology 12
edition-
4) Monheims Local anesthesia and pain control in dental
practice
5) Human anatomy vol 3- B D Chaurasia
6) Burkets oral medicine 11 edition- Greenberg,
Glick,ship

42. QUESTIONS
 What are nociceptors?
 What is dermatomal rule?
 Types of pain?
 What is pain perception?
 Theories of pain?

43.  What is saltatory conduction?
 What is pyschogenic pain?

45. THANK YOU