pain

1. Physiology of pain
&
withdrawal reflex
Dr. Sai Sailesh Kumar G
Associate Professor
Department of Physiology
NRIIMS
Email: dr.goothy@gmail.com

4. Learning objectives
Describe the theories of pain
Describe the pathways of pain transmission
Describe the pain suppression mechanism
Explain referred pain

5. Introduction
Pain occurs whenever tissues are being damaged
It causes individual to react to remove the pain stimulus
After spinal cord injury, the person lose pain sensation
Fails to feel the pain

6. Types of pain
Fast pain - felt within 0.1 sec after a pain stimulus applied
Slow pain – begins only after 1 sec or more and increases slowly
over many seconds and some time minutes
Fast pain/ sharp pain/ pricking pain/electric pain/acute pain- type
of pain felt when needle is stuck in the skin, skin cut with knife,
skin is acutely burned

7. Types of pain
Slow pain/ slow burning pain/aching pain/throbbing
pain/nauseous pain/ chronic pain
This type of pain causes tissue destruction
Occur in skin and deep tissues

8. Pain receptors
Free nerve endings
Wide spread in the superficial layers of skin and internal
tissues
A delta fibers – fast pain
C fibers – slow pain

9. Pain stimulus
Mechanical – fast pain, slow pain
Thermal – fast pain, slow pain
Chemical – slow pain

10. Non-adapting pain receptors
slow adapting receptors

11. Dual pain pathway
 Fast pain – A delta fibers
 Neo spinothalamic pathway
 Velocity 6-30 m/sec
 Slow pain – C fibers
 Paleo spinothalamic pathway
 Velocity 0.5-2 m/sec

12. Lateral spinothalamic pathway
Pain pathway
Dual pathway
Fast pain- Neo-spinothalamic pathway
Slow pain- Paleo-spinothalamic pathwaty

13. Neo- spinothalamic pathway
Fast type A delta fibers transmit mainly mechanical and acute
thermal pain
They terminate in the lamina I ( lamina marginalis) of the dorsal
horns
The second order neurons originates and cross immediately to
the opposite side of the spinal cord through anterior commissure

15. Neo- spinothalamic pathway
Second order neurons ascends via medulla, pons, midbrain
Few fibers terminates in the reticular areas of brain stem
Most of the fibers pass to the VPLN of thalamus
Third order neurons arises and pass through the posterior limb of
internal capsule and corona radiata and terminates in the post
central gyrus of cerebral cortex area 3,1,2.

17. Paleo- spinothalamic pathway
Much older system
Transmits slow-chronic pain
Type C fibers
Substance P is neuro transmitter
First order neurons terminates in the lamina 2 and lamina 3 (
together called as substansia gelatinosa)

18. Paleo- spinothalamic pathway
 From there short axons arises and terminates in the lamina 5
 Second order neurons arises from lamina 5 and crosses the midline
immediately to opposite side in anterior commissure
 Ascends through medulla, pons, midbrain
 Most of the fibers terminates in the brain stem at reticular nuclei, tectal
area and periaqueductal gray region
 Only one tenth fibers reach thalamus

21. Localization
Fast sharp pain can be localized much more exactly than
slow chronic pain

22. Neurotransmitters
A delta fibers – glutamate
C fibers- substance P

23. Removal of somatosensory cortex
Do not prevent pain perception
Pain impulses entering the brain stem reticular formation,
thalamus and lower brain centers cause conscious
perception of pain
Cortex plays a important role in interpreting the pain quality

24. Cordotomy
When a person has severe and intractable pain
Resulting from rapidly spreading cancer
It is necessary to relieve pain
If the pain is in the lower part of the body, a cordotomy in the
thoracic region of the spinal cord relieves pain for few weeks to
few months

25. Cordotomy
Spinal cord on the side opposite to the pain is partially cut in
the anterolateral quadrant
Interruption of anterolateral sensory pathways

26. Cauterize
Another operative procedure to relieve pain
Cauterize specific areas in the intralaminar nuclei in the
thalamus
Relieves suffering type of pain

27. Analgesia system in the brain
Analgesia system
Periaquiductal gray matter and periventricular areas of the
mesencephalon and upper pons
Nuerons from these areas signals to
Raphe magnus nucleus located in lower pons and upper medulla
and nucleus reticularis para gigantocellularis

28. Analgesia system in the brain
From these second order signals are transmitted down the
dorso lateral columns of the spinal cord
Pain inhibitory complex is located in the dorsal horns of the
spinal cord
Block pain signals before it relay in brain

29. Analgesia system in the brain
Neurotransmitters involved
Enkephalin
Serotonin
Analgesia system can block pain signals at the initial entry
point to the spinal cord.

30. Gate control theory
1965
Melzack and wall
Stimulation of tactile receptors
Activation of the dorsal column pathway
AB fibers from the tactile receptors
Lateral inhibition of pain pathway

31. Gate control theory
Rubbing the skin near painful area relieves pain
Basis for acupuncture

33. Peripheral nerve sectioning
Somatic nerve sectioning is must
One problem is there can be complete loss of all sensations
in the affected part of the body

34. Sympathectomy
From viscera pain sensation is carried by the sympathetic
afferent fibers
Sympathectomy
Relieves pain

35. Posterior rhyzotomy
Cutting the lateral division of the spinal cord
Selective loss of pain and temperature

36. Myelotomy
Fibers crossing the anterior gray and white commissure are
cut off
Spinothalamic tract are cut off

37. Prefrontal lobotomy
White matter connection of pre frontal lobe with other parts of
cerebral cortex is cutoff
Person can feel as thalamus is intact
But person reaction to pain is absent

38. Referred pain
Pain in the viscera
Not felt at the site of origin
But felt in some superficial part of the body far away from the
site of origin of pain
Ischaemic heart pain is referred to inner part of left arm

39. Referred pain
Pain in diaphragm is referred to the tip of the shoulder
Pain in the appendix is referred around umbilicus region
Dermatomal rule: the visceral part of the body takes origin
from a particular dermatome in embryonic life from which the
superficial part also taken origin

40. Referred pain
Convergence theory:
Both pain pathways from skin and visceral organs terminate on
same second-order neuron
Skin is most prone to get damaged than viscera
Brain interprets that the pain impulses are from skin
Pain felt on superficial area

41. Referred pain
Convergence theory:
Both pain pathways from skin and visceral organs terminate on
same second-order neuron
Skin is most prone to get damaged than viscera
Brain interprets that the pain impulses are from skin
Pain felt on superficial area

43. Hyper algesia
Hyper sensitivity to pain
Primary hyper algesia- extreme sensitivity of sunburned skin
Secondary hyperalgesia- lesion of thalamus

44. Herpes zoster
Herpes virus infects DRG
Severe pain in the dermatomal segment subserved by the
ganglion
Herper zoster or shingles

45. Tic Doulourex
Lancinating or stabbing pain one side of face in the sensory
distribution of trigeminal nerve or glossopharyngeal nerve
Trigeminal neuralgia
Glossopharyngeal neuralgia
Pain like sudden electric shock and it persists few seconds
Sensory part of the nerves has to be cut to relieve pain

46. Brown-Sequard syndrome
If the spinal cord is transected only one side
All motor functions are blocked on the side of transaction
below the level of transection
Some of the sensations lost on the transected side and
others lost opposite side

47. Brown-Sequard syndrome
Pain and temperature are lost on the opposite side of the
body in all dermatomes two to six segments below level of
transection
Functions carried by dorsal column lost on the same side
below level of transection

48. THANK YOU