PAIN

ANATOMY&PHYSIOLOGY

Dr. M.ANEEQUE ALAM

Anesthesia Resident

Department of Anesthesiology

Patel Hospital

aneeque86@gmail.com

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

NOCICEPTION

Nocioception is a complex sequence of actions

between tissue damage and the perception of

pain.Its includes

Transduction

Transmission

Modulation

Perception

Transduction: Translation of a (chemical) pain

stimulus into electrical activity on nerve level.

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

Modulation: Modification of the nociceptive

transmission through a number of humoral and

neural effects

anti-nociceptive pathways

(descending pathway)

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

Opioids

Local anesthetics

Opioids

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).

CLASSIFICATION

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.

PRIMARY AFFERENT FIBERS

Aδ – fast

C – slow

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

TYPE OF PAIN

FAST PAIN

SLOW PAIN

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

THE NEUROCHEMICALS OF PAIN

• Glutamate - Central

• Substance P - Central

• Brandykinin - Peripheral

• Prostaglandins - Peripheral

PAIN

INITIATOR

• Serotinin

• Endorphins

• Enkephalins

• Dynorphin

PAIN

INHIBITOR

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

Second order neuron: Has cell body in the

spinal cord ormedulla oblongata

• Starts from substantiagelatinosa

Axon decussate & Terminate on 3rd order

in thalamus neuron followingSpinothalamic tract

Third order neuron: Has cell body in thalamus Axon terminates on cerebral cortex ipsilaterally

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

GATE THEORY

Melzack & Wall (1965)

. non-painful input closesthe "gates" to painful input

APPLICATIONS OF GATE THEORY

Stimulation of touch fibres for pain relief:

TENS (transcutaneous electrical nerve

stimulation)

Acupuncture

Massage

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.

Hyperalgesia

AllodyniaPain due to a stimulus that does not

normally provoke pain.

Increased pain from a stimulus that

normally provokes pain

PAIN FELT AWAY FROM THE ORIGINAL SITE OF THE

PAINFUL STIMULUS.

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

QUESTIONS?