PAIN Prof Ashraf Husain Classification of pain Pain

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. 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. 3

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CHARACTERISTICS OF PRIMARY AFFERENT 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 6

CHARACTERISTICS OF PRIMARY AFFERENT FIBRES C – Fiber: • Non-Myelinated • Diameter less than 2 f. lm. -0. 5 to 2 m/s conduction velocity • Te. Jrninate in I and n layers • Slow, diffuse, dull, aching • Neurotransmitter - P-Substance • 80% of pain conduction 7

NOCICEPTOR: PAIN RECEPTOR TYPES: 1. HIGH TRHESHOLD MECHANORECEPTOR(HTM) NNERVATED BY - TIHN MYELINATED A FIBERS 2. POLYMODAL NOCICEPTORS(PMN) INNERVATED BY UNMYELINATED C FIBRES 8

DAMAGE AND INFLAMMATION RELEASE CHEMICAL MEDIATORS WICH ACTIVATE OR SENSITISE THE RECEPTOR ENDINGS CYTOKl. NES BRADYKININ, PROSTAGLANDIN, P - SUBSTANCE RESULTS IN TRANSDUCTION CONDUCTION OF NERVE IMPULSE 9

DORSAL HORN GATING MECHANISM 10

A MODAL OF “GATING” OF PAIN 11

Ascending Pathway 12

Descending Analgesic Pathway 13

ASCENDING AND DESCENDING PAIN PATHWAYS 14

Neurotransmitters in Analgesic Pathway 15

Referral of pain from the internal organs Organ Site of reffered pain • Meninges • Heart Back of head and neck Central chest arms (usually left), neck, occasionally abdomen. Behind sternum Shoulder tip Behind sternum Cont… 16 • Trachea • Diaphragm • Oesophagus

Organ Site of reffered pain • Stomach, duodenum Upper abdomen, epigastrium • Small bowel, pancreas Around umbilicus • Large bowel, bladder Lower abdomen above pubic bone 17

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VISCERAL PAIN 19

VISCERAL PAIN PATHWAY Pain - Aδ and fibers Travel with autonomic afferent Spinal cord (Dorsal Horn) Lat. spinothalamic tract Thalamus Somatosensory Cortex 20

CHARACTERSITICS OF VISCERAL PAIN • 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 21

TERMS FREQUENTLY USED • 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. 22

TERMS FREQUENTLY USED Thalamic Syndrome. Obstruction of the thalmogeniculate branch of the posterior cerebral artery Affects posterior thalamic nuclei. . Prolonged severe pain. 23

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SITES & MECHANISM OF PAIN RELIEF 25

Trans Coetaneous Electrical Nerve Stimulation (TENS) 26

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