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PAIN

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PAIN. Prof. Ashraf Husain. Classification of pain. Pain perception is affected by the context in which it is experienced. Pain is arbitrarily categorized into somatic - superficial and deep - and visceral pain. Visceral pain is sometimes referred to another site. - PowerPoint PPT Presentation

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PAIN

Prof. Ashraf Husain

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Classification of pain• Pain perception is affected by the context

in which it is experienced. • Pain is arbitrarily categorized into somatic

- superficial and deep - and visceral pain.• Visceral pain is sometimes referred to

another site.• Structures to which the pain. is referred

are innervated by the same spinal segment as the origin of the pain.

• Pain may arise from phantom limbs or be triggered by inappropriately mild stimulation in abnormal conditions.

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CHARACTERISTICS OF PRIMARYAFFERENT FIBRES

A δ Fiber:• Myelinated -• Diameter fine 2 - 5 μm• 12 - 30 m/sec. conduction velocity• Terminated at I and V layer• Fast pain, rapid, pricking and well localized• Neurotransmitter - Glutamate • 20% pain conduction

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• Non-Myelinated

• Diameter less than 2 f.lm .-0.5 to 2 m/s conduction velocity

• TeJrninate in I and n layers

• Slow, diffuse, dull, aching

• Neurotransmitter - P-Substance

• 80% of pain conduction

CHARACTERISTICS OF PRIMARYAFFERENT FIBRES

C – Fiber:

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TYPES:

1. HIGH TRHESHOLD

MECHANORECEPTOR(HTM) NNERVATED BY

- TIHN MYELINATED A FIBERS

2. POLYMODAL NOCICEPTORS(PMN)

INNERVATED BY UNMYELINATED C FIBRES

NOCICEPTOR: PAIN RECEPTOR

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DAMAGE AND INFLAMMATION

RELEASE CHEMICAL MEDIATORS WICH ACTIVATEOR

SENSITISE THE RECEPTOR ENDINGS

CYTOKlNES BRADYKININ, PROSTAGLANDIN, P - SUBSTANCE

RESULTS IN TRANSDUCTION

CONDUCTION OF NERVE IMPULSE

10DORSAL HORN GATING MECHANISM

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A MODAL OF “GATING” OF PAIN

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Ascending Pathway

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Descending AnalgesicPathway

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ASCENDING AND DESCENDING PAIN PATHWAYS

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Neurotransmitters in AnalgesicPathway

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Referral of pain from the internal organs

• Meninges Back of head and neck• Heart Central chest arms

(usually left), neck, occasionally abdomen.

• Trachea Behind sternum• Diaphragm Shoulder tip• Oesophagus Behind sternum

Cont…

Organ Site of reffered pain

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• Stomach, duodenum Upper abdomen, epigastrium

• Small bowel, pancreas Around umbilicus• Large bowel, bladder Lower abdomen

above pubic bone

Organ Site of reffered pain

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VISCERAL PAIN

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VISCERAL PAIN PATHWAY

Pain - Aδ and fibersTravel with autonomic afferent

Spinal cord(Dorsal Horn)

Lat. spinothalamic tract

Thalamus

Somatosensory Cortex

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• Poorly localized• Associated with nausea and autonomic disturbance• Often referred to another part of the body• Cutting, crushing are not painful when applied to viscera• Pain is caused by distension, ischemia and inflammation

CHARACTERSITICS OF VISCERAL PAIN

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• Hyperalgesia: Excessive Pain• Allodynia: Pain caused by any other sensation

e.g. touch will cause pain.• Muscular Pain: Less blood flow in the muscles

(ischemia).• Stress analgesia: Mild degree of pain is not felt if

the other part of the body has excessive pain.• Causalgia: Burning pain.

TERMS FREQUENTLY USED

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Thalamic Syndrome.Obstruction of the thalmogeniculate branch of the posterior cerebral artery Affects posterior thalamic nuclei.. Prolonged severe pain.

TERMS FREQUENTLY USED

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SITES & MECHANISM OF PAIN RELIEF

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Trans Coetaneous Electrical Nerve Stimulation

(TENS)

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