- Pain is an unpleasant sensory and emotional experience caused by actual or potential tissue damage. It serves a protective function by making us aware of damage. - Pain has two components - awareness of the stimulus and the emotional response. It is classified as somatic or visceral. - The pathway involves nociceptors detecting damage and transmitting signals through three neurons - first order detect pain and transmit to the spinal cord, second order transmit to the brain, and third order transmit to the somatosensory cortex where conscious perception occurs.

1. PAIN
Acknowledge to
Dr. Dhwani Gohil
Shamima Akter
B. Sc (Honors) in Occupational Therapy
& M. Sc in Rehabilitation Science
Assistant Professor,
Department of Occupational Therapy
Bangladesh Health Professions Institute (BHPI)
Centre for the Rehabilitation of the Paralysed (CRP)
Chapain, Savar

2. Pain
• Pain is the protective mechanism of the body
when any tissue is being damaged.
• But it has two features which are nearly
universal.
• First, it is an unpleasant experience; and
secondly, it is evoked by a stimulus which is
actually or potentially damaging to living tissues.
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3. CONTINUE…
• That is why, although it is unpleasant, pain
serves a protective function by making us
aware of actual or impending damage to the
body.
• Like all sensory experiences, pain has two
components, the first component is the
awareness of a painful stimulus and the
second is the emotional impact (or effect)
evoked by the experience.
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4. CLASSIFICATION OF PAIN
PAIN
Somatic
(somasthetic)
Visceral (from viscera)
e.g. angina pectoris,
peptic ulcer, intestinal
colic, renal colic, etc.
Superficial (from skin &
subcutaneous tissue) e.g.
superficial cuts/burns, etc.
Deep (from
muscles/bones/fascia/periosteum)
e.g. fractures/arthritis/fibrositis,
rupture of muscle belly
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5. Types of pain
– Fast pain: The pain which felt within about 0.1
second after a pain stimulus is applied, is called
fast pain. Alternative names of fast pain are sharp
pain, pricking pain, acute pain and electrical pain.
Receptor: Free nerve ending
Types of fiber: Aδ fiber
Termination: Somatosensory area of cerebral
cortex
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6. Continue…
– Slow pain: The pain which begins only after 1
second or more and then in 1 second or more and
then increases slowly over many seconds and
minutes. Alternative names of slow pain are
burning pain, aching pain, throbbing pain,
nauseous pain and chronic pain.
Receptor: Free nerve ending
Types of fiber: C fiber
Termination: Intralaminar nuclei of thalamus
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7. Causes of pain
• Tissue damage
• Tissue ischaemia
• Muscle spasm
• Irritation or over distension of viscera
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8. Pathway of pain- Lateral spinothalamic
tract
Pain Stimuli (mechanical, thermal, chemical)
Pain receptor (Free nerve ending)
Afferent nerve (Fast pain- Aδ fiber and slow pain- C fiber)
Dorsal root ganglion (1st order neuron)
Posterior horn cell of same side (2nd order neuron)
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9. Continue..
Crosses the white comissure goes to lateral funiculus of
opposite side
Ascend as lateral spinothalamic tract
Medulla
Midbrain
Thalamus (Here slow pain ends, but for fast pain 3rd order
neuron begins)
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10. Continue…
• Slow pain end in the intra laminar nuclei of
thalamus
• Fast pain goes to the somatosensory area of
cerebral cortex (Brodmann’s area 2)
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12. Details Pain Pathway
• Pain receptors in the skin and other tissue are
free nerve ending.
• The pain impulses are transmitted to the
spinal fibers and slow conducting C type
fibers.
• The axon entering the spinal cord from
posterior root ganglia proceed to the tip of the
posterior gray column and divide into
ascending branches.
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13. Continue..
• These branches travels for a distance of one
two segment of spinal cord and from the
posterior lateral tract of lissauer.
• The axon of the 2nd order neuron now cross
obliquely to the opposite side in the anterior
gray and white commissure within one spinal
segment of the cord ascending in the
contralateral white column as the lateral
spinothalamic tract.
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14. Continue..
• As the lateral spinothalamic tract ascends
through the spinal cord new fibers added to
the anteromedial aspect of the tract, so that
in the upper cervical segments of the cord the
sacral fibers are medial.
• As the spinothalamic tract ascends through
the medulla oblongata, it is accompanied by
the anterior spinothalamic tract, together they
from the spinal lemniscuses.
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15. Continue…
• These fibers of first order neuron terminate by
synapse with cells in the posterior gray
column, including cells in the substantia
gelatinosa.
• The spinal lemniscuses continues to ascend
through the posterior part of the pons and
midbrain.
• Many of the fibers of the lateral spinothalamic
tract end by synapsing with a third order
neuron in the thalamus.
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16. Continue…
• It is believed that here crude pain is
appreciated and emotional reaction are
initiated.
• The axon of the third neuron in the ventral
posteriolateral nucleus of the limb of internal
capsule and coronaradiata to reach the so
esthetic area in the post central gyrus area in
the post central gyrus in the cerebral cortex.
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17. Continue…
• The contralateral half is represented as inverted
with the hand and mouth situated inferiorly, and
the leg situated superiorly and with the foot and
an genital region on the medial surface of
hemisphere.
• From here, information is transmitted to other
regions of the cerebral cortex to be used by
motor areas and partial association area.
• The role of cerebral cortex is interpreting the
quality of the sensory information at the level of
consciousness.
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18. Referred pain
• Pain in an area removed from the site of tissue
injury is called referred pain.
• The presumed mechanism is that afferent
fibres from the site of tissue injury enter the
spinal cord at a similar level to afferents from
the point to which the pain is referred.
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19. Paresthesia
• A Paresthesia is any abnormal sensation.
• It may be spontaneous or evoked. The most
common Paresthesia is the sense of “pins and
niddles” when a nerve in a limb is
compressed. The limb ‘falls asleep’.
• Paresthesia is not always painful.
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20. Phantom pain
• it is pain felt in a part of the body that has been
surgically removed. It is common for patients to have
phantom pain post-operatively; that is, after limb
amputation.
• The patient feels as though the limb were still present.
• This sensation occurs in nearly all patients undergoing
amputation.
• It usually subsides over days to weeks. A small
percentage of patients develop true phantom limb
pain, which may be extraordinarily persistent and
resistant to treatment.
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21. • A nerve ending that responds to noxious stimuli that can
actually or potentially produce tissue damage.
• Free nerve endings i.e., they are not enclosed in a capsule.
The receptors for fast pain are sensitive to mechanical or
thermal stimuli of noxious strength.
• The receptors for slow pain are sensitive not only to noxious
mechanical and thermal stimuli but also to a wide variety of
chemicals associated with inflammation.
• These substances include histamine, serotonin, bradykinin,
acetylcholine, potassium ions and hydrogen ions.
• It is possible that noxious mechanical and thermal stimuli
also act through the release of some of these chemicals.
NOCICEPTORS
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22. • Nociception is the neural mechanism by which an
individual detects the presence of a potentially tissue
harming stimulus.
• There is no implication of (or requirement for) awareness
of this stimulus.
• The nociceptive mechanism (prior to the perceptive event)
consists of a multitude of events as follows:
• Transduction
• Transmission
• Modulation
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Continue…
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23. Transduction:
• This is the conversion of one form of energy to another. It occurs at a
variety of stages along the nociceptive pathway.
Transmission:
• Electrical events are transmitted along neuronal pathways, while
molecules in the synaptic cleft transmit information from one cell
surface to another.
Modulation:
• The adjustment of events, by up- or down regulation. This can occur at
all levels of the nociceptive pathway, from tissue, through primary (1°)
afferent neurone and dorsal horn, to higher brain centres.
• Thus, the pain pathway as described by Descartes has had to be adapted
with time.
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24. SENSORY NEURONS
First Order Second Order Third Order
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25. First Order Neuron
• Each sensory receptor is attached to a first order primary
afferent neuron that carries the impulses to the CNS.
• The axons of these first-order neurons are found to have
varying thickness.
• It has long been known that a relationship exists between the
diameter of nerve fibers and their conduction velocities.
• The larger fibers conduct impulses more rapidly than smaller
fibers.
• A general classification of neurons divides the larger fibers from
the smaller ones.
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26. Second Order Neuron
• The primary afferent neuron carries impulse into the CNS and
synapses with the second-order neuron.
• This second-order neuron is sometimes called a transmission
neuron since it transfers the impulse on to the higher centers.
• The synapse of the primary afferent and the second-order
neuron occurs in the dorsal horn of the spinal cord.
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27. Third Order Neuron
• Cell bodies of third order neurons of the nociception-relaying
pathway are housed in: the ventral posterior lateral, the ventral
posterior inferior, and the intralaminar thalamic nuclei
• Third order neuron fibers from the thalamus relay thermal sensory
information to the somesthetic cortex.
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