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.
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
CHARACTERISTICS OF PRIMARYAFFERENT FIBRES C – Fiber: • 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
NOCICEPTOR: PAIN RECEPTOR • TYPES: • HIGH TRHESHOLD MECHANORECEPTOR(HTM) NNERVATED BY - TIHN MYELINATED A FIBERS • POLYMODAL NOCICEPTORS(PMN) INNERVATED BY UNMYELINATED C FIBRES
DAMAGE AND INFLAMMATION RELEASE CHEMICAL MEDIATORS WICH ACTIVATE OR SENSITISE THE RECEPTOR ENDINGS CYTOKlNES BRADYKININ, PROSTAGLANDIN, P - SUBSTANCE RESULTS IN TRANSDUCTION CONDUCTION OF NERVE IMPULSE
Descending Analgesic Pathway
Neurotransmitters in Analgesic Pathway
Referral of pain from the internal organs Organ Site of reffered pain • 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 • Stomach, duodenum Upper abdomen, epigastrium • Small bowel, pancreas Around umbilicus • Large bowel, bladder Lower abdomen above pubic bone
VISCERAL PAIN PATHWAY Pain - Aδ and fibers Travel with autonomic afferent Spinal cord (Dorsal Horn) Lat. spinothalamic tract Thalamus Somatosensory Cortex
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
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.
TERMS FREQUENTLY USED Thalamic Syndrome .Obstruction of the thalmogeniculate branch of the posterior cerebral artery Affects posterior thalamic nuclei. . Prolonged severe pain.
Trans Coetaneous Electrical Nerve Stimulation (TENS)