This document discusses pain anatomy and physiology. It defines pain as an unpleasant sensory and emotional experience associated with tissue damage. Nociception is the process by which nociceptors detect and transmit signals of potential tissue damage to the brain. There are different types of nociceptors and pain fibers that detect fast, sharp pain or slow, dull pain. The ascending pain pathway involves three neurons that transmit nociceptive signals from receptors to the spinal cord and thalamus. The gate control theory proposes that non-painful input can close the "gates" and inhibit pain transmission.

1. PAIN
ANATOMY&PHYSIOLOGY
Dr. M.ANEEQUE ALAM
Anesthesia Resident
Department of Anesthesiology
Patel Hospital
aneeque86@gmail.com

2. DEFINITION
Pain is unpleasant sensory and
emotional experience associated
with actual or potential tissue
damage, or described in terms of
such damage.
Ref: International Association for the Study of Pain(IASP)
o Pain is SUBJECTIVE phenomena

3. NOCICEPTION
 Nocioception is a complex sequence of actions
between tissue damage and the perception of
pain.Its includes
 Transduction
 Transmission
 Modulation
 Perception

4.  Transduction: Translation of a (chemical) pain
stimulus into electrical activity on nerve level.

5.  Transmission: Guidance of the pain – information
through the nervous system, including:
Ascending pathway
 Primary afferent nerve-ends that go to the dorsal horn of
the spinal cord.
 ascending (inter-) neurons that project their information
from the spinal cord to the brainstem and
the hypothalamus/thalamus
 The thalamic-cortical pathways

6.  Modulation: Modification of the nociceptive
transmission through a number of humoral and
neural effects
 anti-nociceptive pathways
(descending pathway)

7.  Perception: Observing the pain in
a conscious way. Integration of transduction,
transmission and modulation with the unique
psychology of the individual, resulting in a
subjective and emotional pain sensation

8. Opioids
Local anesthetics
Opioids

9. CLASSIFICATION
PAIN IS CLASSIFIED INTO NOCICEPTIVE, NEUROPATHIC AND
PSYCHOGENIC
 1. Nociceptive is pain caused by tissue damage (inflammation)
which stimulate pain receptors (nociceptors).
2. Neuropathic: (pain due to injury of nerve pathway)
site of injury: Central Central pain (thalamic infarct).
Mixed Plexus avulsion, Post herpetic neuralgia.
Peripheral Neuroma, nerve compression, phantom, neuralgias.
character: burning, tingling, numbness, pressing, squeezing, itching, constant +/-
intermittent shooting, lancinating, electric.
3. Psychogenic: (difficult to differentiate whether secondary to or actual
cause of pain), anxiety, depression (30% of depressives complain of pain on initial
presentation).

10. Nociceptors are special receptors that
respond only to noxious stimuli and generate
nerve impulses which the brain interprets as “pain”
 Free nerve endings
oNon adaptive it’s a
protective function
to keep the individual
trying to remove the
damaging stimulus or
to get away from it.

11. PRIMARY AFFERENT FIBERS
Aδ – fast
C – slow

12. CHARACTERISTICS A DELTA FIBRES C-FIBRES
MYLENATION MYELINATED
LARGE DIAMETER
NON-MYLENATED
SMALL DIAMETER
CONDUCTION SPEED FAST(70-120 m/sec) SLOW(0.2-2 m/sec)
ONSET FIRST
FAST PAIN
SECOND
SLOW PAIN
DURATION BRIEF LONG
RECEPTIVE FIELD SMALL LARGE
LOCALIZATION PRECISE DIFFUSE
SENSORY QUALITY SHARP,PRICKING ACHING,DULL,
BURNING
CNS RESPONSE RELFEX,ANALYSIS EMOTIONAL,
SUFFERING

13. TYPE OF PAIN
FAST PAIN
SLOW PAIN

14. FAST PAIN SLOW PAIN
onset: during application of the stimulus Shortly after application if tissue damage
occurs
Duration: short duration Longer duration
Nature: pricking Burning
Afferent: A-delta fibers C-fibers
Neurotransmitter: glutamate Substance-P
Significance: * determine site & severity.
* Initiate withdrawal reflexes.
Associated with arousal, autonomic &
emotional reactions
Localization: well-localized Poorly-localized

15. THE NEUROCHEMICALS OF PAIN
• Glutamate - Central
• Substance P - Central
• Brandykinin - Peripheral
• Prostaglandins - Peripheral
PAIN
INITIATOR
• Serotinin
• Endorphins
• Enkephalins
• Dynorphin
PAIN
INHIBITOR

16. PAIN’S ASCENDING PATHWAY TO THE
BRAIN
THREE neurons from the receptor
to the cerebral cortex
 First order neuron:
 Cell body located in the
dorsal root ganglion.
 Starts from free nerve ending
 Ends at substantia gelatinosa

17.  Second order neuron:
 Has cell body in the
spinal cord or
medulla oblongata
• Starts from substantia
gelatinosa
 Axon decussate &
 Terminate on 3rd order
in thalamus
neuron following
Spinothalamic tract
 Third order neuron:
 Has cell body in thalamus
 Axon terminates on
cerebral cortex ipsilaterally

18. The Descending Pathway
 pain afferents stimulates the neurons in
periaqueductal gray (PAG) - gray matter
surrounding the cerebral aqueduct in the
midbrain results in activation of efferent anti-nociceptive
pathways
 from there the impulses are transmitted
through the spinal cord to the dorsal horn
 there thay inhibit or block transmission of
nociceptive signals at the level of dorsal horn

21. GATE THEORY
Melzack & Wall (1965)
. non-painful input closes
the "gates" to painful input

22. APPLICATIONS OF GATE THEORY
Stimulation of touch fibres for pain relief:
 TENS (transcutaneous electrical nerve
stimulation)
 Acupuncture
 Massage

24. PAIN TOLERANCE
 It is the maximum intensity of pain can be tolerated by the
subject without obvious complaint.
 Pain tolerance is affected by a number of factors:
- Anxiety, depression & fatigue ------>  pain tolerance.
- rest, sever exercise & strong emotional excitement ------>  pain tolerance.

25. Hyperalgesia
Increased pain from a stimulus that
normally provokes pain
Allodynia
Pain due to a stimulus that does not
normally provoke pain.

26. PAIN FELT AWAY FROM THE ORIGINAL SITE OF THE
PAINFUL STIMULUS.

27. PHANTOM LIMB
o sensations are described as
perceptions that an individual experiences
relating to a limb or an organ that is not
physically part of the body
o brain contains neuromatrix of the
body image –neurosignature like a
hologram

28. QUESTIONS?